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Hydroponics

History | A New Angle | Growing Tips| Systems |  Media | Lighting  | Nutrients | Temperature & Humidity | Plants

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Glossary of Terms

TRADUZCA Y HAGA DISPONIBLE ESTA PAGINA WEB EN CUALQUIER OTRO IDIOMA, UTILIZANDO EL TRADUCTOR DE GOOGLE.

History of Hydroponics

Hydroponics basically means working water ("hydro" means "water" and "ponos" means "labor"). Many different civilizations have utilized hydroponic growing techniques throughout history. As noted in Hydroponic Food Production (Fifth Edition, Woodbridge Press, 1997, page 23) by Howard M. Resh: "The hanging gardens of Babylon, the floating gardens of the Aztecs of Mexico and those of the Chinese are examples of 'Hydroponic' culture. Egyptian hieroglyphic records dating back several hundred years B.C. describe the growing of plants in water." Hydroponics is hardly a new method of growing plants. However, giant strides have been made over the years in this innovative area of agriculture.

Throughout the last century, scientists and horticulturists experimented with different methods of hydroponics. One of the potential applications of hydroponics that drove research was for growing fresh produce in nonarable areas of the world. It is a simple fact that some people cannot grow in the soil in their area (if there is even any soil at all). This application of hydroponics was tested during World War II. Troops stationed on nonarable islands in the Pacific were supplied with fresh produce grown in locally established hydroponic systems. Later in the century, hydroponics was integrated into the space program. As NASA considered the practicalities of locating a society on another plant or the Earth's moon, hydroponics easily fit into their sustainability plans. This research is ongoing.

But by the 1970s, it wasn't just scientists and analysts who were involved in hydroponics. Traditional farmers and eager hobbyists began to be attracted to the virtues of hydroponic growing. A few of the positive aspects of hydroponics include:

• The ability to produce higher yields than traditional, soil-based agriculture
• Allowing food to be grown and consumed in areas of the world that cannot support crops in the soil
• Eliminating the need for massive pesticide use (considering most pests live in the soil), effectively making our air, water, soil, and food cleaner

Commercial growers are flocking to hydroponics like never before. The ideals surrounding these growing techniques touch on subjects that most people care about, such as helping end world hunger and making the world cleaner. In addition to the extensive research that is going on, everyday people from all over the world have been building (or purchasing) their own systems to grow great-tasting, fresh food for their family and friends. Educators are realizing the amazing applications that hydroponics can have in the classroom. And ambitious individuals are striving to make their dreams come true by making their living in their backyard greenhouse, selling their produce to local markets and restaurants.

And now that so many people from so many different walks of life are involved in hydroponics and its associated disciplines (such as aeroponics and aquaponics), progress is coming faster than ever before.

A New Angle

For many traditional backyard gardeners, the thought of hydroponics evokes images of sterile, white labs with test-tube-wielding scientists tending to obscure plants in protective bubbles. This scenario may be true in some cases, but in reality anyone can become a hydroponic gardener. You're working with the same plants--just from a new angle.

Hydroponics allows you to garden year-round because you have complete control over light, humidity, and temperature, resulting in greater high-quality yields in a smaller space. Although some aspects of hydroponics may seem a bit involved, getting started doesn't have to be overwhelming. With a little planning and information, a hydroponic garden can be within your reach faster than you might have believed!

Beginner's Growing Tips

This page has been designed to help answer the important questions beginning growers might have when just getting started in hydroponics. A lot of these concepts are connected to each other. Follow the links and put the pieces of this growing puzzle together.

The more you know, the easier it is to grow!

Carbon Dioxide

During photosynthesis, plants use carbon dioxide (CO2), light, and hydrogen (usually water) to produce carbohydrates, which is a source of food. Oxygen is given off in this process as a by-product. Light is a key variable in photosynthesis.

Conductivity

Measuring nutrient solution strength is a relatively simple process. However, the electronic devices manufactured to achieve this task are quite sophisticated and use the latest microprocessor technology. To understand how these devices work, you have to know that pure water doesn’t conduct electricity. But as salts are dissolved into the pure water, electricity begins to be conducted. An electrical current will begin to flow when live electrodes are placed into the solution. The more salts that are dissolved, the stronger the salt solution and, correspondingly, the more electrical current that will flow. This current flow is connected to special electronic circuitry that allows the grower to determine the resultant strength of the nutrient solution.

The scale used to measure nutrient strength is electrical conductivity (EC) or conductivity factor (CF). The CF scale is most commonly used in hydroponics. It spans from 0 to more than 100 CF units. The part of the scale generally used by home hydroponic gardeners spans 0-100 CF units. The part of the scale generally used by commercial or large-scale hydroponic growers is from 2 to 4 CF. (strength for growing watercress and some fancy lettuce) to as high as approximately 35 CF for fruits, berries, and ornamental trees. Higher CF values are used by experienced commercial growers to obtain special plant responses and for many of the modern hybrid crops, such as tomatoes and some peppers. Most other plant types fall between these two figures and the majority is grown at 13-25 CF.
--Rob Smith

Germination

When a seed first begins to grow, it is germinating. Seeds are germinated in a growing medium, such as perlite. Several factors are involved in this process. First, the seed must be active--and alive--and not in dormancy. Most seeds have a specific temperature range that must be achieved. Moisture and oxygen must be present. And, for some seeds, specified levels of light or darkness must be met. Check the specifications of seeds to see their germination requirements.

The first two leaves that sprout from a seed are called the seed leaves, or cotyledons. These are not the true leaves of a plant. The seed develops these first leaves to serve as a starting food source for the young, developing plant.

Growing Medium

Soil is never used in hydroponic growing. Some systems have the ability to support the growing plants, allowing the bare roots to have maximum exposure to the nutrient solution. In other systems, the roots are supported by a growing medium. Some types of media also aid in moisture and nutrient retention. Different media are better suited to specific plants and systems. It is best to research all of your options and to get some recommendations for systems and media before making investing in or building an operation. Popular growing media include:

• Composted bark. It is usually organic and can be used for seed germination.
• Expanded clay. Pellets are baked in a very hot oven, which causes them to expand, creating a porous end product.
• Gravel. Any type can be used. However, gravel can add minerals to nutrient. Always make sure it is clean.
• Oasis. This artificial, foam-based material is commonly known from its use as an arrangement base in the floral industry.
• Peat moss. This medium is carbonized and compressed vegetable matter that has been partially decomposed.
• Perlite. Volcanic glass is mined from lava flows and heated in furnaces to a high temperature, causing the small amount of moisture inside to expand. This converts the hard glass into small, sponge-like kernels.
• Pumice. This is a glassy material that is formed by volcanic activity. Pumice is lightweight due to its large number of cavities produced by the expulsion of water vapor at a high temperature as lava surfaces.
• Rockwool. This is created by melting rock at a high temperature and then spinning it into fibers.
• Sand. This medium varies in composition and is usually used in conjunction with another medium.
• Vermiculite. Similar to perlite except that it has a relatively high cation exchange capacity--meaning it can hold nutrients for later use.

There are a number of other materials that can (and are) used as growing media. Hydroponic gardeners tend to be an innovative and experimental group.

Hydroponic Systems

The apparatuses used in hydroponic growing are many and varied. There are two basic divisions between systems: media-based and water culture. Also, systems can be either active or passive. Active systems use pumps and usually timers and other electronic gadgets to run and monitor the operation. Passive systems may also incorporate any number of gadgets. However, they to not use pumps and may rely on the use of a wicking agent to draw nutrient to the roots.

Media-based systems--as their name implies--use some form of growing medium. Some popular media-based systems include ebb-and-flow (also called flood-and-drain), run-to-waste, drip-feed (or top-feed), and bottom-feed.

Water culture systems do not use media. Some popular water culture systems are raft (also called floating and raceway), nutrient film technique (NFT), and aeroponics.

Light

Think of a plant as a well-run factory that takes delivery of raw materials and manufactures the most wondrous products. Just as a factory requires a reliable energy source to turn the wheels of its machinery, plants need an energy source in order to grow.

Artificial Light

Usually, natural sunlight is used for this important job. However, during the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light (for photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum (wavelength or color of light) suitable for plant life, different types of artificial lighting are selected for specific plant varieties and optimum plant growth characteristics. Different groups of plants respond in physically different ways to various wavelengths of radiation. Light plays an extremely important role in the production of plant material. The lack of light is the main inhibiting factor in plant growth. If you reduce the light by 10 percent, you also reduce crop performance by 10 percent.

Light transmission should be your major consideration when purchasing a growing structure for a protected crop. Glass is still the preferred material for covering greenhouses because, unlike plastic films and sheeting, its light transmission ability is indefinitely maintained.

No gardener can achieve good results without adequate light. If you intend to grow indoors, avail yourself of some of the reading material that has been published on this subject. If you are having trouble growing good plants, then light is the first factor to question.
--Rob Smith

Natural Light

A large part of the success in growing hydroponically is planning where to place the plants. Grow plants that have similar growing requirements in the same system. Placing your system 1-2 feet away from a sunny window will give the best results for most herbs and vegetables. Even your regular house lights help the plants to grow. Make sure that all of the lights are out in your growing area during the night. Plants need to rest a minimum of 4 hours every night. If your plants start to get leggy (too tall and not very full), move the system to a spot that has more sun. Once you find a good growing area, stick to it. Plants get used to their home location. It may take some time to get used to a new place.
--Charles E. Musgrove

Macronutrients

Plants need around 16 mineral nutrients for optimal growth. However, not all these nutrients are equally important for the plant. Three major minerals--nitrogen (N), phosphorus (P), and potassium (K)--are used by plants in large amounts. These three minerals are usually displayed as hyphenated numbers, like "15-30-15," on commercial fertilizers. These numbers correspond to the relative percentage by weight of each of the major nutrients--known as macronutrients--N, P, and K. Macronutrients are present in large concentrations in plants. All nutrients combine in numerous ways to help produce healthy plants. Usually, sulfur (S), calcium (Ca), and magnesium (Mg) are also considered macronutrients.

These nutrients play many different roles in plants. Here are some of their dominant functions:

• Nitrogen (N)--promotes development of new leaves
• Phosphorus (P)--aids in root growth and blooming
• Potassium (K)--important for disease resistance and aids growth in extreme temperatures
• Sulfur (S)--contributes to healthy, dark green color in leaves
• Calcium (Ca)--promotes new root and shoot growth
• Magnesium (Mg)--chlorophyll, the pigment that gives plants their green color and absorbs sunlight to make food, contains a Mg ion
  --Jessica Hankinson

Micronutrients

Boron (B), copper (Cu), cobalt (Co), iron (Fe) manganese (Mn), molybdenum (Mo), and zinc (Zn) are only present in minute quantities in plants and are known as micronutrients. Plants can usually acquire adequate amounts of these elements from the soil, so most commercial fertilizers don't contain all of the micronutrients. Hydroponic growers, however, don't have any soil to provide nutrients for their plants. Therefore, nutrient solution that is marketed for hydroponic gardening contain all the micronutrients.
--Jessica Hankinson

Nutrient Solution

In hydroponics, nutrient solution--sometimes just referred to as "nutrient"--is used to feed plants instead of plain water. This is due to the fact that the plants aren't grown in soil. Traditionally, plants acquire most of their nutrition from the soil. When growing hydroponically, you need to add all of the nutrients a plant needs to water. Distilled water works best for making nutrient. Hydroponic supply stores have a variety of nutrient mixes for specific crops and growth cycles. Always store solutions out of direct sunlight to prevent any algae growth. See also conductivity, macronutrients, and micronutrients.

Disposal Unlike regular water, you need to be careful where you dispose of nutrient. Even organic nutrients and fertilizers can cause serious imbalances in aquatic ecosystems. If you do not live near a stream, river, lake or other water source, it is fine to use old nutrient on outdoor plants and lawn. Another possibility is to use it on houseplants. However, if you live within 1,000 feet of a viable water source, do not use your spent nutrient in the ground.

Osmosis

The ends of a plant’s roots aren’t open-ended like a drinking straw and they definitely doesn’t suck up a drink of water or nutrients (see capillary action). Science is still seeking a complete understanding of osmosis, so to attempt a full and satisfactory description of all that’s involved in this process would be impossible. However, we can understand the basic osmotic principle as it relates to plants.

First, consider a piece of ordinary blotting paper, such as the commonly used filter for home coffee machines. The paper might appear to be solid. However, if you apply water to one side of it, you’ll soon see signs of the water appearing on the opposite side. The walls of a feeding root act in much the same way. If you pour water onto the top of the filter paper, gravity allows the water to eventually drip through to the bottom side. Add the process of osmosis and water that’s applied to the bottom side drips through to the top.

With plants, this action allows water and nutrients to pass through the root walls from the top, sides, and bottom. Osmosis is the natural energy force that moves elemental ions through what appears to be solid material. A simplistic explanation for how osmosis works, although not 100 percent accurate, is that the stronger ion attracts the weaker through a semipermeable material. So, the elements within the cells that make up plant roots attract water and nutrients through the root walls when these compounds are stronger than the water and nutrients applied to the outside of the roots.

It then follows that if you apply a strong nutrient to the plant roots--one that’s stronger than the compounds inside of the root--that the reverse action is likely to occur! This process is called reverse osmosis. Many gardeners have at some time committed the sin of killing their plants by applying too strong a fertilizer to their plants, which causes reverse osmosis. Instead of feeding the plant, they have actually been dragging the life force out of it.

Understanding how osmosis works, the successful grower can wisely use this knowledge to promote maximum uptake of nutrients into the plants without causing plant stress--or worse, plant death--from overfertilizing. All plants have a different osmotic requirement or an optimum nutrient strength.
--Rob Smith

Oxygen

As a result of the process of photosynthesis, oxygen (O) is given off by plants. Then, at night, when light isn't available for photosynthesis, this process is reversed. At night, plants take in oxygen and consume the energy they have stored during the day.

Pests and Diseases

Even though hydroponic gardeners dodge a large number of plant problems by eschewing soil (which is a home to any number of plant enemies), pests and diseases still manage to wreak havoc from time to time. Botrytis, Cladosporium, Fusarium, and Verticillium cover most of the genera of bacteria that can threaten your plants. The insects that can prove annoying include aphids, caterpillars, cutworms, fungus gnats, leaf miners, nematodes, spider mites, thrips, and whiteflies.

A few good ways to prevent infestation and infection are to:

• Always maintain a sanitary growing environment
• Grow naturally selected disease- and pest-resistant plant varieties
• Keep your growing area properly ventilated and at the correct temperatures for your plants
• Keep a close eye on your plants so if a problem does occur, you can act quickly

With insects, sometimes you can pick off and crush any large ones. Or you can try to wash the infected plants with water or a mild soap solution (such as Safer Soap).

If a problem gets out of control, it may be necessary to apply a biological control in the form of a spray. Research which product will work best in your situation. Always follow the instructions on pesticides very closely.

Alternatively, there are a number of control products on the market today that feature a botanical compound or an ingredient that has been synthesized from a plant material.

On botanical compounds as controlling agents:

Over the last few years, researchers from all around the world have started to take a much closer look at any compounds present in the plant kingdom that might hold the answer to our pest and disease control problems. Many companies have even switched from producing synthetic pesticides to copying nature by synthesizing naturally occurring compounds in a laboratory setting. Extracts of willow, cinnamon, grapefruit, garlic, neem, bittersweet, lemon grass, derris, eucalyptus, and tomato have been helpful in controlling diseases and pests.
--Dr. Lynette Morgan

pH

The pH of a nutrient solution is a measurement of its relative concentration of positive hydrogen ions. Negative hydroxyl ions are produced by the way systems filter and mix air into the nutrient solution feeding plants. Plants feed by an exchange of ions. As ions are removed from the nutrient solution, pH rises. Therefore, the more ions that are taken up by the plants, the greater the growth. A solution with a pH value of 7.0 contains relatively equal concentrations of hydrogen ions and hydroxyl ions. When the pH is below 7.0, there are more hydrogen ions than hydroxyl ion. Such a solution "acidic." When the pH is above 7.0, there are fewer hydrogen ions than hydroxyl ions. This means that the solution is "alkaline."

Test the pH level of your nutrient with a kit consisting of vials and liquid reagents. These kits are available at local chemistry, hydroponic, nursery, garden supplier, or swimming pool supply stores. It is also a good idea to test the pH level of your water before adding any nutrients. If your solution is too alkaline add some acid. Although such conditions rarely occur, sometimes you may have to reduce the level of acidity by making the solution more alkaline. This can be achieved by adding potassium hydroxide (or potash) to the solution in small amounts until it is balanced once again.
--Charles E. Musgrove

Photosynthesis

Plants need to absorb many necessary nutrients from the nutrient solution or--in the case of traditional agriculture--the soil. However, plants can create some of their own food. Plants use the process of photosynthesis to create food for energy. Carbohydrates are produced from carbon dioxide (CO2) and a source of hydrogen (H)--such as water--in chlorophyll-containing plant cells when they are exposed to light. This process results in the production of oxygen (O).

Plant Problems

Every now and again, you are sure to run into a problem with your plants. This is just a simple fact of any type of gardening. The key is to act quickly, armed with quality knowledge.

Mineral Deficiency Symptoms

Nitrogen deficiency will cause yellowing of the leaves, especially in the older leaves. The growth of new roots and shoots is stunted. In tomatoes, the stems may take on a purple hue.

A phosphorous deficiency is usually associated with dark green foliage and stunted growth. As in nitrogen deficiency, the stems may appear purple. But since the leaves don't yellow as they do in nitrogen deficiency, the whole plant can take on a purplish green color.

Iron deficiency results in yellowing between the leaf veins. In contrast to nitrogen deficiency, the yellowing first appears in the younger leaves. After a prolonged absence of iron, the leaves can turn completely white.
--Jessica Hankinson

Wilting

This condition can be caused by environmental factors or disease (usually caused by Fusarium). Nutrient and media temperature can be adjusted to remedy wilt. However, if Fusarium have taken hold, the chances that your plants will survive are slim.

If wilting is due to environmental causes:

Try to spray the plants and roots with cool, clean water to rejuvenate them. If this hasn’t helped them by the next day, try it again. If the plants respond, top-off the nutrient solution and check the pH. If the plants don’t respond to the misting, empty the tank, move it to a shadier spot, and refill with cool, fresh nutrient solution. Don’t reuse the old solution--start with fresh water and nutrients.
--Charles E. Musgrove

If wilting is due to a system blockage of nutrient:

I have seen tomato plants that have been so dehydrated due to a nutrient supply blockage that they were lying flat and for all the world looked stone-cold dead. When the nutrient flow resumed and the plants were given the less stressful environment of nighttime, they rebounded so well that I wondered if I had dreamed the previous day’s "disaster." The moral of this story is to always give plants a chance to revive, even when the situation looks hopeless.
--Rob Smith

See also pests and diseases.

Propagation

Plants can be propagated by a number of methods. Growers can let a plant go to seed, collect the seeds, and then start the cycle over again (see germination). Another method is to take stem cuttings, which is also known as cloning (because you are creating an exact copy of the parent plant).

Although this process won't work with all plants, it is a highly effective technique. Simply cut off a side shoot or the top of the main shoot just below a growth node. Make sure that there are at least two growth nodes above the cut. Remove any of the lower leaves near the base of the new plant. This cutting can then be rooted by placing it in water or in a propagation medium (perlite works well) that is kept moist. The use of some rooting hormone can help your chances of success.

Pruning

Remove any discolored, insect-eaten, or otherwise sick-looking leaves from plants. Picking off some outer leaves or cutting the top off a plant can help it grow fuller. Use sharp scissors to prune your plants. Sometimes you will want to prune a plant to focus its energy on the remaining shoots. Pruning is an art and should be performed with care. Damaged or dying roots may also need to be pruned from time to time.

Soil

Never use soil during any aspect of hydroponics. If you ever move a plant from a soil-based situation to hydroponics, remove all traces of soil or potting mix from the roots. Soil holds lots of microbes and other organisms and materials that love to grow in and contaminate your hydroponic system. Some of these will actually parasitize your plant and slow its growth. This is another advantage of hydroponic growing: The plant can get on with growing without having to support a myriad of other organisms as happens in conventional soil growing.
--Rob Smith

Temperature

Different plants have different germination and growing temperatures. Always make sure that you check each plant’s growing requirements--especially minimum and maximum temperature levels. Keep in mind that specific varieties of plants may have different requirements.

Water

Because the water supply is the source of life for your plants, quality is important. All plants rely on their ability to uptake water freely. Between 80 and 98 percent of this uptake is required for transpiration (loosely compared to perspiration in animals), which allows the plant to produce and somewhat control its immediate microclimate. Plants also need clean, uncontaminated water to produce their own healthy food supply.
--Rob Smith

The water you use in your hydroponic system needs to be pure. It is always a good idea to test your water source before adding nutrients so you aren't adding an element that is already present. In small systems, it would be wise to use distilled water.

If you are starting a larger hydroponic operation, it would be a good idea to have a water analysis completed. Factors such as sodium chloride (NaCl, or salt) content and hardness will be of great use to growers. Also, groundwater can have elements normally not present in conditioned water. A key piece of advice: Get to know your water!

Systems

Choosing the right system--whether you decide to build it or buy it--can make or break your hydroponic gardening experience.

Carefully consider your available space, lighting, budget, and time constraints before purchasing any equipment or settling on a unit to build yourself. Also think about what you want to grow, whether you may want to expand, and recurring costs.

Hydroponic systems can be "active" or "passive." They also can be "media-based" or "water culture." Active systems rely on a pump to flow nutrient around the plant's roots and to provide aeration. Passive systems work without a pump. A wicking material draws nutrients up to the roots or the root tips are suspended in a stationary solution with the main portion of the rootball hanging in the air.

Media-based systems, such as ebb-and-flow (flood-and-drain), top-feed (drip), or bottom-feed systems rely on a growing medium to support the plants and hold nutrient solution around their roots. Most operate on timers, alternately wetting the medium to wash out salts and replenish nutrients and then draining so the plants can draw in atmospheric oxygen.

Water culture systems usually operate without media. Sometimes rockwool cubes or small amounts of gravel are used because plants like tomatoes and cucumbers get top heavy when they start to bear fruit and may need help to stand upright. You can also use plastic flaps, foam rings, fiber cups, or plastic collars for plant support. Some growers tie plants to a trellis.

Media-Based

The best feature of media-based systems is their ability to hold nutrients and moisture between watering cycles so plants can survive a temporary breakdown or power outage. But with that security comes the cost and mess associated with the growing media. Some gravel media can even leach mineral substances into the solution, resulting in chemical imbalances. Nevertheless, media-based systems remain popular--especially among beginners--because of their relative simplicity and reliability.

Ebb-and-flow systems function by flooding and draining a medium-filled growing bed with nutrient solution. In its basic form, the ebb-and-flow unit consists of a growing tray and reservoir bucket connected by a tube. The tray is flooded by manually raising the bucket and drained by lowering it. By adding a pump and timer, the basic unit evolves into an automatic hydroponic system.

Top-feed or drip systems work with a timer-controlled pump that delivers nutrient solution slowly and regularly to the base of the plant roots through thin tubing or drip emitters. The solution trickles through the medium back to the reservoir below the growing bucket. Media such as expanded clay pellets or perlite distribute the nutrient in a wide circle around the plant roots.

Drip systems are flexible. You can adjust the nutrient flow for individual plants within the same system by changing the number of emitters or their size, allowing plants with different nutrient and water requirements to be grown together.

Although drip systems are easy to set up, construct, and operate, maintenance can be a problem, especially if you use organics in your nutrient solution. The emitters clog on occasion and then need thorough cleaning.

See the self-watering potted plant in the Easy Hydroponic System Plans section for a basic example of a media-based grower.

Water Culture

Because they lack media to store water and nutrients, water culture systems need a continuous flow of nutrients to prevent drying out plant roots. Thus, the plants are more at risk from power outages and mechanical failures. But without medium, recurring costs and waste disposal are reduced and the balance of nutrient solution is uneffected. They also are more compact and lightweight than media-based systems. Stacked or vertical nutrient film technique (NFT) channels produce an amazing harvest in a surprisingly small space--and look nice too.

Although several different types of water culture systems are available, not all are appropriate for beginners. NFT is the most popular water culture system. This is a channel-type system where plants are supported with rockwool cubes, cups, or collars and their roots dangle in triangular pipes or round tubes. Nutrient solution runs along the bottom of the channels so just the root tips are submerged. The main portion of the rootball hangs in the air. Capillary mats are often used in the bottom of the channels to help distribute the growing roots evenly for better aeration. Hybrid, media-based NFT systems have media-filled troughs instead of empty gutters.

See the media-free jar system in the Easy Hydroponic System Plans section for a basic example of a water culture grower.

Further Reading

• "The Growing World of Hydroponics" by Rob Smith, The Growing Edge, Vol. 11, No. 4

Media

A good hydroponic medium should support the plants in the system, not break down, absorb and retain moisture, be porous to allow air circulation and proper drainage, and protect plant roots from temperature extremes. Different media are suitable for different crops. Commonly used media for hydroponic culture are:

Coconut Fiber

A fairly new hydroponic medium, coconut fiber is porous, long-lasting, all-natural, and features good oxygen and water-retention properties. It's much like rockwool, but it doesn't irritate the skin when dry. Also, it's biodegradable, so disposal doesn't pose a problem.

Expanded Clay

If you buy a drip or ebb-and-flow system kit from a dealer, it will probably come equipped with expanded clay pellets for the medium. Like perlite, clay pellets are porous and retain water and air well. Expanded clay is dusty, so it will need to be rinsed before it goes into your system.

Perlite

Perlite is lightweight, stable, and has good water-retention properties. Like most media, perlite must be rinsed before you fill your system with it.

Rockwool

Rockwool is an inorganic, sterile, inert growing medium made from a combination of basalt rock, limestone, and silica. It's available in various-sized propagating blocks, wrapped cubes, and large slabs. Commercial growers prefer rockwool over other media because it's light, relatively inexpensive, safe for immediate use, and has the best water- and air-holding capacities. Although rockwool is nontoxic, when dry it can cause skin irritation. If this occurs, simply wash your hands for instant relief.

Sand

Although sand is one of the oldest hydroponic media, it's heavy when wet and tends to dry out quickly. However, it's long-lasting, easy to keep clean, inexpensive, and in plentiful supply. If you choose sand for those reasons, be sure to buy coarse sand, not fine. The latter drains poorly.

Vermiculite

When used in hydroponics, vermiculite is often mixed 1:5 or 1:10 with perlite or clay pellets. The problem with vermiculite--and the main reason it's not used alone--is that it tends to break down after a year or so, which leads to clogging and stagnation.

Some other media used are:

• Composted bark
• Gravel
• Oasis
• Peat Moss
• Pumice

Light

During the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light (for photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum (wavelength or color of light) suitable for plant life, different types of artificial lighting are selected for specific plant varieties and optimum plant growth characteristics. Different groups of plants respond in physically different ways to various wavelengths of radiation. Light plays an extremely important role in the production of plant material.

No gardener can achieve good results without adequate light. If you intend to grow indoors, avail yourself of some of the reading material that has been published on this subject. If you are having trouble growing good plants, then light is the first factor to question.
--Rob Smith

A number of lighting options exist for hydroponic gardeners. Two considerations must first be evaluated: What type of hydroponic system you are going to use and where are you are planning to situate it. Once you have answered those two questions, you will have significantly narrowed your options.

Some commercial and hobbyist hydroponic growers--especially in temperate or tropical regions--work outdoors. This especially makes sense in tropical areas, since they can grow outdoors all year long. Otherwise, growers simply work outside during the appropriate seasons.

Incandescent bulbs (the most common type used in the home) pass electricity through a fine filament (usually tungsten). The filament heats up, glows, and gives off heat. These bulbs are cheap and work with universal sockets. However, they do not supply a full enough spectrum to be adequate for most growing needs.

If you need to supply artificial light, you have some choices. The best option for an indoor grower with limited or no natural light is to use a high intensity discharge (HID) setup. HID lights flow electricity through vaporized gas under high pressure. The best HIDs for growing are metal halide (MH) and high-pressure sodium (HPS) lamps. One big difference between these bulb types is that MHs can be used from seed germination through bloom. Usually, HPS lamps are only used during bloom cycles. Also, MH lamps more closely resemble natural sunlight. One downside with these lamps is cost: They can be expensive (up to $300 for the ballast, base, and bulb).

One economical alternative for beginners is to use fluorescent lights. A setup of ballast, base, and bulb should only run around $20. In order to maximize results, you will need to use different bulb types during different growing cycles. Each type of fluorescent bulb puts out a different spectrum. Warm white bulbs gives off more red light, which is good for flowering. Cool white bulbs give off more blue light, which is good for vegetative growth. Fluorescent bulbs are pretty inexpensive, so you should be able to purchase both types.

Another consideration is how many lights you will need. The variables involved here are the type of plants you are growing, how many plants you are growing (usually measured in total square feet of plants), and the wattage of the bulbs you will be using. Many growing consultants and equipment merchants believe that 20-40 watts per square foot is an acceptable level of light. Remember that plants have different light requirements and needed periods of rest. Check plant requirements before shopping.

Greenhouse Growing

Some areas are blessed with enough natural sunlight year-round that growers do not need to supplement with artificial light. However, if you are growing commercially, or you don't get enough natural light, you may need to include some artificial lights in the greenhouse. These can be used on an on-demand basis, such as on cloudy days. Other greenhouses always supplement a low level of light for their plants.

Indoor Growing

For a beginning experiment in indoor hydroponics, there isn't anything wrong with simply placing your system by a sunny window. If you catch the indoor gardening bug and decide to develop a more sophisticated (or just larger) system, dedicated lighting will probably be necessary.

Further Reading

• "Artificial Lighting in Horticulture," by Bill Lermer, The Growing Edge, Vol. 2 No. 3
• "Lighting for Beginners Part 1: The Meaning of Light," by Don Parker, The Growing Edge, Vol. 5 No. 4
• "Lighting for Beginners Part II: Let There Be Light," by Don Parker, The Growing Edge, Vol. 6 No. 1

Nutrients and Water

Leave the mixing of hydroponic nutrients to the chemistry wizards. Many ready-made nutrient solutions that contain all of the necessary macronutrients and micronutrients that most plants will need. These solutions have been specially created for hydroponics. Don't haphazardly use fertilizers developed for use on soil-based plants. Most of these products contain residues that could clog hydroponic systems.

Also, the concept is different (and the creators of these different nutrients are well aware of that fact). Soil-based fertilizers are meant to supplement the minerals and matter in your soil. In hydroponics, the nutrient solution is all your plants can rely on for external nutrition (for information on how plants create some of their own food, see photosynthesis). In many ways, this simplification of variables works in your favor in hydroponics.

Hydroponic supply stores have a variety of nutrient mixes for specific crops and growth cycles. Always store mixed solutions out of direct sunlight to prevent any algae growth. For related discussions involving nutrient solution, see conductivity, macronutrients, micronutrients, mineral deficiency, and pH.

Any gardener needs to be confident about their water quality. This is especially true for hydroponic gardeners. The water you use in your hydroponic system needs to be pure. It is always a good idea to test your water source before adding nutrients so you aren't adding an element that is already present. In small systems, it would be wise to use distilled water.

If you are starting a larger hydroponic operation, it would be a good idea to have a water analysis completed. Factors such as sodium chloride (NaCl, or salt) content and hardness will be of great use to growers. Also, groundwater can have elements normally not present in conditioned water. A key piece of advice: Get to know your water!

Further Reading

• "The Chemical Dynamics of Hydroponic Nutrient Solutions," by Erik Ackerson, The Growing Edge, Vol. 1 No. 2
• "Water Should Taste Good -- to plants!" by Dr. Cal C. Herrmann and Lawrence L. Brooke, The Growing Edge, Vol. 1 No. 4
• "The Growing World of Hydroponics," by Rob Smith, The Growing Edge, Vol. 10 No. 3

Temperature and Humidity

Different plants have different recommended germination and growing temperatures. Always make sure that you check each plant’s growing requirements--especially minimum and maximum temperature levels. Keep in mind that specific varieties of plants may have different requirements.

Indoors or out, most fruits and vegetables grow best between 55 and 85ºF. Try to keep your temperature around 75ºF if possible during the day and around 65ºF at night. If you are growing indoors, remember that plants dislike drafts.

Most people won't run into humidity problems (unless they live in a rain forest or desert). If the air is too dry or wet, you might want to invest in a humidifier, dehumidifier, or a combination unit. If your plants are too dry, misting them with water will help raise the relative humidity.

Keep in mind that too much humidity and warm temperatures can be conducive to the growth of many fungal diseases (see pests and diseases). Maintaining proper environmental conditions, using sterile supplies, and paying quality attention to your plants is the best way to ensure proper growth and prevent diseases.

Plants

You can grow just about anything hydroponically that you can when using traditional techniques. Chances are, your favorite plants will thrive in their new conditions. Basil, beans, broccoli, Brussels sprouts, cabbage, cantaloupe, carrots, cauliflower, chilies, chives, cucumbers, eggplant, lettuce (and various other salad greens), mint, peppers, radishes, spinach, strawberries, tomatoes, and watermelon are all common hydroponic crops. Certain growing systems and conditions work better together with some crops. It is a good idea to do some research to find out what will work best for your situation.

Hydroponic plants can be started just like traditional plants. They can be grown from seed in germinating medium and then transplanted. Remember that the plant's roots need to be cleaned before transplanting to a hydroponic system. This is especially important if a plant is ever going from a soil-based situation to hydroponics. Seeds can also be sown directly in rockwool starter cubes that can then be transferred to a growing system. Many plants can also be started from cuttings. For more information on starting plants from seed, see germination; for more information on starting plants from cuttings, see propagation.

Further Reading

• Virtually every issue of The Growing Edge covers the aspects involved in growing some sort of plant. Search back issues to find information on specific plants in the store -- and keep your eyes open! The Growing Edge Web Site and magazine will always have more vital data to explore!

Windowsill Wonder

Anyone can build a simple, automated hydroponic system without spending a lot of money. This system is compact enough to fit on a kitchen windowsill--although it can easily be expanded to accommodate any growing plant collection. All the materials that are needed for this system can be found at discount superstores, aquarium supply stores, or hardware stores for under $25.

We used a 2-liter bottle for the nutrient reservoir and an ice cube holding bin for the plant trough. Once you comprehend the logistics, feel free to experiment with other containers. To prepare your nutrient reservoir, drill two holes in the cap of the 2-liter bottle. The holes should be just big enough to snugly hold the 1/4-inch straight through connectors. One hole will be for the water line and the other will be for the air line. Drill a hole in the side of the trough (the ice cube holding bin) as close to the bottom as possible. If you plan on expanding your system, drill another hole on the opposite side. Insert the straight through connectors in the drilled holes. Create a quality seal around the connectors with glue or silicon caulk.

Create your water distribution hose by drilling several small holes in a piece of irrigation tubing cut to fit the bottom of the trough. Connect one end of the tube to one of the fittings on the inside of the trough. The other end of the tube can be sealed with a dab of glue or caulk. If you plan on expanding your system, don't seal the other end. Instead, connect it to the other fitting on the opposite side of the trough. Connect the water line from the nutrient reservoir to the trough. Cut another piece of water line to about the same length as your nutrient reservoir. Then connect this line to the other side of the water line connector, on the inside of the bottle cap. The line should hang down to the bottom of the 2-liter bottle when the cap is on.

Run the air line from the air pump to the other straight through connector on the cap of the bottle. At some point in the air line, splice the line to put in the T connector. Off the T, connect the aquarium air line bleed valve.

Fill your 2-liter bottle with water until it's about three-quarters full. Reconnect it to your trough and place the trough where it will be situated. Turn on the air pump and close the air valve. The water will be pushed into the trough. Gradually ease open the valve until the water is moving into the trough very slowly. It's okay if it takes up to a half-hour for the air pump to push all the water out of the bottle. The goal here is to have the valve closed enough to allow adequate pressure to build inside the bottle to push the water out, but open enough to allow air to escape when the pump is off, so the water can flow back into the bottle.

Now you're ready to add the medium and plants. We found that expanded clay or lava rock works well. Any number of plants will work in this system. Succulent herbs, such as basil and mint, are particularly easy to grow.

If you want to expand your system, simply build another trough and attach the incoming water line of the new trough to the end of the previous trough. We found that up to two modules of this size could be powered from the same pump and nutrient bottle.

Flooding and draining the system once a day should be adequate. But if you're growing a large plant in a sunny location, you may have to set the system to flood and drain twice a day.

Materials

Air pump, Timer, Plastic tubing, 2-liter bottle, Straight through connectors, T connector, Bleed valve, Ice cube holding bin, Medium, Waterproof glue or silicon caulk, Drill

This easy hydroponic system was first profiled in Growing Notes "Hydroponics on a Budget," by Jessica Hankinson and Sean Weise, The Growing Edge, Vol. 11, No. 6.

Cooler Float Grower

In the early days of winter 2001-02, we made some new floating systems out of those "disposable" Styrofoam coolers. Each one costs about $3 new but people are always throwing these coolers away during the summer. If you find one for free, just make sure to give it a good cleaning before using it for a hydroponic system. The coolers we’re currently using are tapered--14 inches long at the top and 12 inches at the bottom. The depth is 8 inches. Since the white Styrofoam will very gradually permit liquids to seep out, we lined the inside of the cooler with two layers of strong plastic, secured with duct tape along the outside rim. We flipped the lids over and cut six spaces on each lid to accommodate the plants. The lids are domed, so when they’re flipped over, they drop down a few inches below the top rim of the cooler. We started our plants in those flimsy black plastic cell trays found at garden centers everywhere (each cell is 2 inches square and trays usually have around 12 cells apiece) in a loose mixture of perlite and vermiculite (about 2:1). The spaces in the cooler lids were cut to accommodate the size of individual cells (just under 2 inches square so the fit is snug).

We feed the seeds with plain water until the plants come up and then switch to a dilute vegetative growth solution (inorganic powder; calcium nitrate, magnesium sulfate, and a "grow" mixture). We usually use Corvallis municipal tap water to mix our nutrient and haven’t had any problems with nutrient imbalances or toxicity.

When the young seedlings are ready, we cut the cells apart, cut the bottom off each cell (make sure your scissors have been sterilized), gently shake out the media (it falls right out), and insert the cells into the cooler lids. The cells fit snugly into the holes and the plant roots easily dangle into the nutrient solution from the start. Oasis or rockwool propagation cubes would probably work for this system as well. The plants should be large enough so the bottom leaves of the plant will support it so it doesn’t slip into the cooler.

We cut a hole into the side of the cooler near the top and to accommodate an air tube connected to an air stone at the bottom of the cooler. An aquarium pump provides constant, gentle, bubbling oxygen. We spilt the air line coming out of the pump and run air tubes to both coolers. One 3-watt pump ably provides oxygen for two coolers. Both coolers easily fit under one of our 250-watt metal halide Hydrofarm Sunburst lights, which is connected to a timer set for a 12-hour photoperiod. Three or four coolers--or a few larger coolers--could probably fit under such a light if reflectors were used. The light is positioned about one foot or more from the plants to make sure they aren’t exposed to too much radiant heat.

Most salad greens and lettuce plants go from seed to harvest in just over a month. If you selectively harvest, once the plants are maturing, you can pull enough greens off for a few salads a day for a few weeks. Don’t wait too long to harvest since overly mature greens can get bitter. Greens will stay nice and fresh in the refrigerator for about a week. If you harvest all at once, you’ll have enough greens for a few mighty salads. If you have new starts continually going and regularly replace old plants with new, you can always have enough greens for the table. The cost of the electricity to run the light and pump (and the cost of the nutrient, which is insignificant) works out to be much less expensive than what you would pay for the greens in the store (about 1/2 as much). And it’s much more fun to grow your own pesticide-free food.

For salad greens, we run a low conductivity solution (an EC of around 0.5-1) and every so often replenish with either water or nutrient--depending on how the plants look and are growing. These systems are situated in the front office window of The Growing Edge in downtown Corvallis, Oregon. There’s a canopy over the sidewalk that blocks most of our direct sunlight, so our herbs and vegetables grow much better under lamps.

Some similar system instructions, as conceptualized by Wally Oi and Charlie Musgrove in Hawaii (they have taught students how to build and operate hydroponic systems on the islands), are on The Growing Edge Web Site (see http://www.growingedge.com/basics/easyplans/ezegro.html).

Materials

Styrofoam cooler, seed-starting trays, seeds, utility knife, scissors, aquarium pump and tubing, air stone, HID lamp (optional), growing medium, nutrient

This easy hydroponic system was adapted from a system first profiled in "A Beginner’s Guide to Hawaiian Hydroponics," 

which was adapted from the instructional manual "Hydroponics In Hawaii Using Black Lava Rock: ‘Eze Gro Kit’" by Charles E. Musgrove, The Growing Edge, Vol. 11, No. 4.

Eze Gro Styrofoam Tank Setup

Use a large, Styrofoam box with a lid for the nutrient tank. Drill 2.5-inch diameter holes through the lid. These holes will hold the root support cups. Drill six 3/4-inch holes along the side at the top of the box, just under the lid. These holes will provide air ventilation.

Locate several Styrofoam cups. These will be the plant supports. Wash and rinse them thoroughly. In hydroponics, everything needs to be very clean! Cut several slots horizontally across the bottoms of the cups with a hack saw. These slots will allow the plant’s roots access to the nutrient solution. The cups will contain a loose growing medium, such as lava cinders, coarse pumice, or perlite. Situate the system on a table or a stand. This will keep your plants away from some pests. Place the cups into the holes in the tank lid. Each cup will hold one strong plant. Fill the nutrient tank with solution to a few inches below the ventilation holes. It's pretty easy to germinate the seeds right in the plant support cups in some sterile, fine sand. The roots will grow down through the medium into the nutrient solution. Stir the solution twice a day to introduce oxygen to the nutrient. The most commonly grown vegetables in the Eze Gro system are green bunching onions and chives, parsley, spinach, lettuce, basil, mint, and watercress.

Media-Free Jar System

The plants will be grown in glass storage jars--pickle jars work well. To prevent the growth of algae, cover the sides of jars with aluminum foil. Hold the plants in place with a lid. Small pieces of Styrofoam cut into circles to fit the mouths of the jars work especially well. You can also use the lid that comes with the jar. The jar will be filled with nutrient solution. If you use the jar's lid, use a pair of tin snips to cut some holes into it. The holes should be about a 1/2 inch in diameter--they need to be more than large enough to accommodate the stems of the growing plants and the pump tubing (see below). Filter floss or polyfill will be used to hold the plants in place. If the lids are made out of metal, line the holes with pieces of plastic tubing to protect the stems from any jagged metal.

An aquarium pump attached to tubing will provide adequate oxygen to the roots. Put the tubing through one of the holes in the jar lid and let it rest on the bottom of the jar. An aquarium air stone should be on the end of the tubing in the jar. The aeration rate should be gentle to avoid damaging the roots.

Materials

Jar, Styrofoam and a knife or jar lid and tin snips, Plant, Aluminum foil, Aquarium pump, tube, and air stone, Filter floss or polyfill, Nutrient

Hint: If you want to use more than one jar, you don't need another pump. Simply buy a three-way splitter for the pump at a pet store.

Self-Watering Potted Plant

Fill the plastic pot with growing medium, such as expanded clay. Gently rinse it with plain, fresh water, allowing the surplus to drain. Place the pot onto the watering saucer. You can set the pot, or pots if you’re going to try several plants, into a shallow plastic tray instead of using a watering saucer. Place a germinated plant into the pot and carefully arrange the roots so that they are distributed through the expanded clay. Pour a small quantity of the prepared nutrient solution into the saucer or tray. The nutrients will be taken up by the plant via capillary action. Check the saucer daily to ensure that the mix doesn’t dry out. Never pour nutrient into the top of the pot; always add the nutrient to the tray or saucer.

Materials

8-inch plastic pot, 10-inch watering saucer, Plant (coleus works well), Growing medium, Nutrient

This easy hydroponic system was first profiled in "The Growing World of Hydroponics," by Rob Smith, The Growing Edge, Vol. 11, No. 1.

A Simple Bed Grower

Flood-and-Drain Bed: This grower can be made from wooden pallets that have legs added or built from scratch. It is filled with growing medium. Add nutrient every day.

Floating Bed: This grower is filled with nutrient. A Styrofoam board floats in the grower. Holes to support growing plants are cut or burned into the board. The nutrient must be stirred twice a day. Remember to regularly monitor the pH.

Bed growers are made out of wood and then lined with plastic. They are usually used outside. If you are using a wooden pallet, all you need to do is attach legs to the corners and line it with plastic. Then, if this is going to be a flood-and-drain bed, you will drill a 2/3-inch hole for the drainage hose, fit the hose into the hole, and shrink the plastic to fit around the hose. Shrinking the plastic around the hose makes sure that nutrient is not wasted by dripping out of the hole. Use a bucket to catch the drained nutrient. Make sure you are familiar with safe nutrient disposal practices.

To build the grower from scratch, start by creating the frame for the bed by nailing the end and side boards together. Then nail the bottom slats onto the rectangular frame. Then nail the legs to each corner and line the bed with black plastic. For the floating bed, cut some holes into a sheet of Styrofoam for the plants to grow through.

Beginner's Growing Tips

This page has been designed to help answer the important questions beginning growers might have when just getting started in hydroponics. A lot of these concepts are connected to each other. Follow the links and put the pieces of this growing puzzle together.

The more you know, the easier it is to grow!

Carbon Dioxide

During photosynthesis, plants use carbon dioxide (CO2), light, and hydrogen (usually water) to produce carbohydrates, which is a source of food. Oxygen is given off in this process as a by-product. Light is a key variable in photosynthesis.

Conductivity

Measuring nutrient solution strength is a relatively simple process. However, the electronic devices manufactured to achieve this task are quite sophisticated and use the latest microprocessor technology. To understand how these devices work, you have to know that pure water doesn’t conduct electricity. But as salts are dissolved into the pure water, electricity begins to be conducted. An electrical current will begin to flow when live electrodes are placed into the solution. The more salts that are dissolved, the stronger the salt solution and, correspondingly, the more electrical current that will flow. This current flow is connected to special electronic circuitry that allows the grower to determine the resultant strength of the nutrient solution.

The scale used to measure nutrient strength is electrical conductivity (EC) or conductivity factor (CF). The CF scale is most commonly used in hydroponics. It spans from 0 to more than 100 CF units. The part of the scale generally used by home hydroponic gardeners spans 0-100 CF units. The part of the scale generally used by commercial or large-scale hydroponic growers is from 2 to 4 CF. (strength for growing watercress and some fancy lettuce) to as high as approximately 35 CF for fruits, berries, and ornamental trees. Higher CF values are used by experienced commercial growers to obtain special plant responses and for many of the modern hybrid crops, such as tomatoes and some peppers. Most other plant types fall between these two figures and the majority is grown at 13-25 CF.
--Rob Smith

Germination

When a seed first begins to grow, it is germinating. Seeds are germinated in a growing medium, such as perlite. Several factors are involved in this process. First, the seed must be active--and alive--and not in dormancy. Most seeds have a specific temperature range that must be achieved. Moisture and oxygen must be present. And, for some seeds, specified levels of light or darkness must be met. Check the specifications of seeds to see their germination requirements.

The first two leaves that sprout from a seed are called the seed leaves, or cotyledons. These are not the true leaves of a plant. The seed develops these first leaves to serve as a starting food source for the young, developing plant.

Growing Medium

Soil is never used in hydroponic growing. Some systems have the ability to support the growing plants, allowing the bare roots to have maximum exposure to the nutrient solution. In other systems, the roots are supported by a growing medium. Some types of media also aid in moisture and nutrient retention. Different media are better suited to specific plants and systems. It is best to research all of your options and to get some recommendations for systems and media before making investing in or building an operation. Popular growing media include:

• Composted bark. It is usually organic and can be used for seed germination.
• Expanded clay. Pellets are baked in a very hot oven, which causes them to expand, creating a porous end product.
• Gravel. Any type can be used. However, gravel can add minerals to nutrient. Always make sure it is clean.
• Oasis. This artificial, foam-based material is commonly known from its use as an arrangement base in the floral industry.
• Peat moss. This medium is carbonized and compressed vegetable matter that has been partially decomposed.
• Perlite. Volcanic glass is mined from lava flows and heated in furnaces to a high temperature, causing the small amount of moisture inside to expand. This converts the hard glass into small, sponge-like kernels.
• Pumice. This is a glassy material that is formed by volcanic activity. Pumice is lightweight due to its large number of cavities produced by the expulsion of water vapor at a high temperature as lava surfaces.
• Rockwool. This is created by melting rock at a high temperature and then spinning it into fibers.
• Sand. This medium varies in composition and is usually used in conjunction with another medium.
• Vermiculite. Similar to perlite except that it has a relatively high cation exchange capacity--meaning it can hold nutrients for later use.

There are a number of other materials that can (and are) used as growing media. Hydroponic gardeners tend to be an innovative and experimental group.

Hydroponic Systems

The apparatuses used in hydroponic growing are many and varied. There are two basic divisions between systems: media-based and water culture. Also, systems can be either active or passive. Active systems use pumps and usually timers and other electronic gadgets to run and monitor the operation. Passive systems may also incorporate any number of gadgets. However, they to not use pumps and may rely on the use of a wicking agent to draw nutrient to the roots.

Media-based systems--as their name implies--use some form of growing medium. Some popular media-based systems include ebb-and-flow (also called flood-and-drain), run-to-waste, drip-feed (or top-feed), and bottom-feed.

Water culture systems do not use media. Some popular water culture systems are raft (also called floating and raceway), nutrient film technique (NFT), and aeroponics.

Light

Think of a plant as a well-run factory that takes delivery of raw materials and manufactures the most wondrous products. Just as a factory requires a reliable energy source to turn the wheels of its machinery, plants need an energy source in order to grow.

Artificial Light

Usually, natural sunlight is used for this important job. However, during the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light (for photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum (wavelength or color of light) suitable for plant life, different types of artificial lighting are selected for specific plant varieties and optimum plant growth characteristics. Different groups of plants respond in physically different ways to various wavelengths of radiation. Light plays an extremely important role in the production of plant material. The lack of light is the main inhibiting factor in plant growth. If you reduce the light by 10 percent, you also reduce crop performance by 10 percent.

Light transmission should be your major consideration when purchasing a growing structure for a protected crop. Glass is still the preferred material for covering greenhouses because, unlike plastic films and sheeting, its light transmission ability is indefinitely maintained.

No gardener can achieve good results without adequate light. If you intend to grow indoors, avail yourself of some of the reading material that has been published on this subject. If you are having trouble growing good plants, then light is the first factor to question.
--Rob Smith

Natural Light

A large part of the success in growing hydroponically is planning where to place the plants. Grow plants that have similar growing requirements in the same system. Placing your system 1-2 feet away from a sunny window will give the best results for most herbs and vegetables. Even your regular house lights help the plants to grow. Make sure that all of the lights are out in your growing area during the night. Plants need to rest a minimum of 4 hours every night. If your plants start to get leggy (too tall and not very full), move the system to a spot that has more sun. Once you find a good growing area, stick to it. Plants get used to their home location. It may take some time to get used to a new place.
--Charles E. Musgrove

Macronutrients

Plants need around 16 mineral nutrients for optimal growth. However, not all these nutrients are equally important for the plant. Three major minerals--nitrogen (N), phosphorus (P), and potassium (K)--are used by plants in large amounts. These three minerals are usually displayed as hyphenated numbers, like "15-30-15," on commercial fertilizers. These numbers correspond to the relative percentage by weight of each of the major nutrients--known as macronutrients--N, P, and K. Macronutrients are present in large concentrations in plants. All nutrients combine in numerous ways to help produce healthy plants. Usually, sulfur (S), calcium (Ca), and magnesium (Mg) are also considered macronutrients.

These nutrients play many different roles in plants. Here are some of their dominant functions:

• Nitrogen (N)--promotes development of new leaves
• Phosphorus (P)--aids in root growth and blooming
• Potassium (K)--important for disease resistance and aids growth in extreme temperatures
• Sulfur (S)--contributes to healthy, dark green color in leaves
• Calcium (Ca)--promotes new root and shoot growth
• Magnesium (Mg)--chlorophyll, the pigment that gives plants their green color and absorbs sunlight to make food, contains a Mg ion
  --Jessica Hankinson

Micronutrients

Boron (B), copper (Cu), cobalt (Co), iron (Fe) manganese (Mn), molybdenum (Mo), and zinc (Zn) are only present in minute quantities in plants and are known as micronutrients. Plants can usually acquire adequate amounts of these elements from the soil, so most commercial fertilizers don't contain all of the micronutrients. Hydroponic growers, however, don't have any soil to provide nutrients for their plants. Therefore, nutrient solution that is marketed for hydroponic gardening contain all the micronutrients.
--Jessica Hankinson

Nutrient Solution

In hydroponics, nutrient solution--sometimes just referred to as "nutrient"--is used to feed plants instead of plain water. This is due to the fact that the plants aren't grown in soil. Traditionally, plants acquire most of their nutrition from the soil. When growing hydroponically, you need to add all of the nutrients a plant needs to water. Distilled water works best for making nutrient. Hydroponic supply stores have a variety of nutrient mixes for specific crops and growth cycles. Always store solutions out of direct sunlight to prevent any algae growth. See also conductivity, macronutrients, and micronutrients.

Disposal Unlike regular water, you need to be careful where you dispose of nutrient. Even organic nutrients and fertilizers can cause serious imbalances in aquatic ecosystems. If you do not live near a stream, river, lake or other water source, it is fine to use old nutrient on outdoor plants and lawn. Another possibility is to use it on houseplants. However, if you live within 1,000 feet of a viable water source, do not use your spent nutrient in the ground.

Osmosis

The ends of a plant’s roots aren’t open-ended like a drinking straw and they definitely doesn’t suck up a drink of water or nutrients (see capillary action). Science is still seeking a complete understanding of osmosis, so to attempt a full and satisfactory description of all that’s involved in this process would be impossible. However, we can understand the basic osmotic principle as it relates to plants.

First, consider a piece of ordinary blotting paper, such as the commonly used filter for home coffee machines. The paper might appear to be solid. However, if you apply water to one side of it, you’ll soon see signs of the water appearing on the opposite side. The walls of a feeding root act in much the same way. If you pour water onto the top of the filter paper, gravity allows the water to eventually drip through to the bottom side. Add the process of osmosis and water that’s applied to the bottom side drips through to the top.

With plants, this action allows water and nutrients to pass through the root walls from the top, sides, and bottom. Osmosis is the natural energy force that moves elemental ions through what appears to be solid material. A simplistic explanation for how osmosis works, although not 100 percent accurate, is that the stronger ion attracts the weaker through a semipermeable material. So, the elements within the cells that make up plant roots attract water and nutrients through the root walls when these compounds are stronger than the water and nutrients applied to the outside of the roots.

It then follows that if you apply a strong nutrient to the plant roots--one that’s stronger than the compounds inside of the root--that the reverse action is likely to occur! This process is called reverse osmosis. Many gardeners have at some time committed the sin of killing their plants by applying too strong a fertilizer to their plants, which causes reverse osmosis. Instead of feeding the plant, they have actually been dragging the life force out of it.

Understanding how osmosis works, the successful grower can wisely use this knowledge to promote maximum uptake of nutrients into the plants without causing plant stress--or worse, plant death--from overfertilizing. All plants have a different osmotic requirement or an optimum nutrient strength.
--Rob Smith

Oxygen

As a result of the process of photosynthesis, oxygen (O) is given off by plants. Then, at night, when light isn't available for photosynthesis, this process is reversed. At night, plants take in oxygen and consume the energy they have stored during the day.

Pests and Diseases

Even though hydroponic gardeners dodge a large number of plant problems by eschewing soil (which is a home to any number of plant enemies), pests and diseases still manage to wreak havoc from time to time. Botrytis, Cladosporium, Fusarium, and Verticillium cover most of the genera of bacteria that can threaten your plants. The insects that can prove annoying include aphids, caterpillars, cutworms, fungus gnats, leaf miners, nematodes, spider mites, thrips, and whiteflies.

A few good ways to prevent infestation and infection are to:

• Always maintain a sanitary growing environment
• Grow naturally selected disease- and pest-resistant plant varieties
• Keep your growing area properly ventilated and at the correct temperatures for your plants
• Keep a close eye on your plants so if a problem does occur, you can act quickly

With insects, sometimes you can pick off and crush any large ones. Or you can try to wash the infected plants with water or a mild soap solution (such as Safer Soap).

If a problem gets out of control, it may be necessary to apply a biological control in the form of a spray. Research which product will work best in your situation. Always follow the instructions on pesticides very closely.

Alternatively, there are a number of control products on the market today that feature a botanical compound or an ingredient that has been synthesized from a plant material.

On botanical compounds as controlling agents:

Over the last few years, researchers from all around the world have started to take a much closer look at any compounds present in the plant kingdom that might hold the answer to our pest and disease control problems. Many companies have even switched from producing synthetic pesticides to copying nature by synthesizing naturally occurring compounds in a laboratory setting. Extracts of willow, cinnamon, grapefruit, garlic, neem, bittersweet, lemon grass, derris, eucalyptus, and tomato have been helpful in controlling diseases and pests.
--Dr. Lynette Morgan

pH

The pH of a nutrient solution is a measurement of its relative concentration of positive hydrogen ions. Negative hydroxyl ions are produced by the way systems filter and mix air into the nutrient solution feeding plants. Plants feed by an exchange of ions. As ions are removed from the nutrient solution, pH rises. Therefore, the more ions that are taken up by the plants, the greater the growth. A solution with a pH value of 7.0 contains relatively equal concentrations of hydrogen ions and hydroxyl ions. When the pH is below 7.0, there are more hydrogen ions than hydroxyl ion. Such a solution "acidic." When the pH is above 7.0, there are fewer hydrogen ions than hydroxyl ions. This means that the solution is "alkaline."

Test the pH level of your nutrient with a kit consisting of vials and liquid reagents. These kits are available at local chemistry, hydroponic, nursery, garden supplier, or swimming pool supply stores. It is also a good idea to test the pH level of your water before adding any nutrients. If your solution is too alkaline add some acid. Although such conditions rarely occur, sometimes you may have to reduce the level of acidity by making the solution more alkaline. This can be achieved by adding potassium hydroxide (or potash) to the solution in small amounts until it is balanced once again.
--Charles E. Musgrove

Photosynthesis

Plants need to absorb many necessary nutrients from the nutrient solution or--in the case of traditional agriculture--the soil. However, plants can create some of their own food. Plants use the process of photosynthesis to create food for energy. Carbohydrates are produced from carbon dioxide (CO2) and a source of hydrogen (H)--such as water--in chlorophyll-containing plant cells when they are exposed to light. This process results in the production of oxygen (O).

Plant Problems

Every now and again, you are sure to run into a problem with your plants. This is just a simple fact of any type of gardening. The key is to act quickly, armed with quality knowledge.

Mineral Deficiency Symptoms

Nitrogen deficiency will cause yellowing of the leaves, especially in the older leaves. The growth of new roots and shoots is stunted. In tomatoes, the stems may take on a purple hue.

A phosphorous deficiency is usually associated with dark green foliage and stunted growth. As in nitrogen deficiency, the stems may appear purple. But since the leaves don't yellow as they do in nitrogen deficiency, the whole plant can take on a purplish green color.

Iron deficiency results in yellowing between the leaf veins. In contrast to nitrogen deficiency, the yellowing first appears in the younger leaves. After a prolonged absence of iron, the leaves can turn completely white.
--Jessica Hankinson

Wilting

This condition can be caused by environmental factors or disease (usually caused by Fusarium). Nutrient and media temperature can be adjusted to remedy wilt. However, if Fusarium have taken hold, the chances that your plants will survive are slim.

If wilting is due to environmental causes:

Try to spray the plants and roots with cool, clean water to rejuvenate them. If this hasn’t helped them by the next day, try it again. If the plants respond, top-off the nutrient solution and check the pH. If the plants don’t respond to the misting, empty the tank, move it to a shadier spot, and refill with cool, fresh nutrient solution. Don’t reuse the old solution--start with fresh water and nutrients.
--Charles E. Musgrove

If wilting is due to a system blockage of nutrient:

I have seen tomato plants that have been so dehydrated due to a nutrient supply blockage that they were lying flat and for all the world looked stone-cold dead. When the nutrient flow resumed and the plants were given the less stressful environment of nighttime, they rebounded so well that I wondered if I had dreamed the previous day’s "disaster." The moral of this story is to always give plants a chance to revive, even when the situation looks hopeless.
--Rob Smith

See also pests and diseases.

Propagation

Plants can be propagated by a number of methods. Growers can let a plant go to seed, collect the seeds, and then start the cycle over again (see germination). Another method is to take stem cuttings, which is also known as cloning (because you are creating an exact copy of the parent plant).

Although this process won't work with all plants, it is a highly effective technique. Simply cut off a side shoot or the top of the main shoot just below a growth node. Make sure that there are at least two growth nodes above the cut. Remove any of the lower leaves near the base of the new plant. This cutting can then be rooted by placing it in water or in a propagation medium (perlite works well) that is kept moist. The use of some rooting hormone can help your chances of success.

Pruning

Remove any discolored, insect-eaten, or otherwise sick-looking leaves from plants. Picking off some outer leaves or cutting the top off a plant can help it grow fuller. Use sharp scissors to prune your plants. Sometimes you will want to prune a plant to focus its energy on the remaining shoots. Pruning is an art and should be performed with care. Damaged or dying roots may also need to be pruned from time to time.

Soil

Never use soil during any aspect of hydroponics. If you ever move a plant from a soil-based situation to hydroponics, remove all traces of soil or potting mix from the roots. Soil holds lots of microbes and other organisms and materials that love to grow in and contaminate your hydroponic system. Some of these will actually parasitize your plant and slow its growth. This is another advantage of hydroponic growing: The plant can get on with growing without having to support a myriad of other organisms as happens in conventional soil growing.
--Rob Smith

Temperature

Different plants have different germination and growing temperatures. Always make sure that you check each plant’s growing requirements--especially minimum and maximum temperature levels. Keep in mind that specific varieties of plants may have different requirements.

Water

Because the water supply is the source of life for your plants, quality is important. All plants rely on their ability to uptake water freely. Between 80 and 98 percent of this uptake is required for transpiration (loosely compared to perspiration in animals), which allows the plant to produce and somewhat control its immediate microclimate. Plants also need clean, uncontaminated water to produce their own healthy food supply.
--Rob Smith

The water you use in your hydroponic system needs to be pure. It is always a good idea to test your water source before adding nutrients so you aren't adding an element that is already present. In small systems, it would be wise to use distilled water.

If you are starting a larger hydroponic operation, it would be a good idea to have a water analysis completed. Factors such as sodium chloride (NaCl, or salt) content and hardness will be of great use to growers. Also, groundwater can have elements normally not present in conditioned water. A key piece of advice: Get to know your water!

Glossary of Terms

Aeroponics: a variation of hydroponics that involves the misting of plant roots with nutrient solution.

Allele: different forms of the same gene; allele "A" may produce a tall plant, while allele "a" gives a short plant.

Anther: part at the top of the male flower that produces the pollen.

Aquaponics: the integration of aquaculture (the raising of marine animals, such as fish) with hydroponics; the waste products from the fish are treated and then used to fertilize hydroponically growing plants.

Bacterial soft rot. See Botrytis.

Bolting: for a plant to prematurely begin the development of a flowering stalk and, subsequently, seed.

Botrytis: any of several fungal diseases that afflict plants; commonly called bacterial soft rot or gray mold.

Capillary action: when the surface of a liquid is in conact with a solid, the liquid is elevated or depressed depending upon the relative attraction of the molecules of the liquid for each other or for those of the solid. This is similar to how plants seemingly defy gravity when they transport liquid from the roots upward through the plant.

Chlorophyll: the green material in plants that is created in the presence of light and is instrumental in photosynthesis.

Cladosporium: any of several fungal diseases that afflict plants; commonly called leaf mold.

Closed system: a hydroponic system, like nutrient film technique (NFT) systems, that recirculates the nutrient solution.

Conductivity: the scale, described as electrical conductivity (EC) or conductivity factor (CF), that is used to measure the strength of nutrient solution.

Cross-pollination: transferring pollen from the flowers of one plant of a species to the stigma of another plant of the same species.

Deficiency. See mineral deficiency.

Dioecious: varieties or species with male and female flowers on separate plants.

Dry rot. See Fusarium.

Electrical conductivity. See conductivity.

F1, F2, F3, etc.: the F1 generation is the result of crossing two different varieties; a cross of two F1 plants produces F2 seed; and so on.

Filament: see stalk.

Fusarium: any of several fungal diseases that afflict plants; commonly called dry rot or wilt.

Germination: the activation of a seed causing it to start to grow; also the production of a pollen tube by a pollen grain

Gray mold. See Botrytis.

Growing medium: materials that are sometimes used in hydroponic growing to support the plant's roots and, sometimes, to hold nutrient.

Insects: a variety of insects attack plants. These include aphids, caterpillars, cutworms, fungus gnats, leaf miners, nematodes, spider mites, thrips, and whiteflies.

Leaf mold. See Cladosporium.

Macronutrients: the major minerals that are used by plants in large amounts, consisting of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg).

Micronutrients: the minor minerals that are used by plants in small amounts, consisting of boron (B), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).

Mineral deficiency: when a plant is not receiving a required nutrient--at all or in an insufficient amount--a disorder will result.

Monoecious: varieties or species with separate male and female flowers on each plant.

Nutrient solution: minerals dissolved in water that are used to feed hydroponically grown plants.

Osmosis: the flow or diffusion that takes place through a semipermeable membrane typically separating a solvent and a solution that strives to bring about a condition of equilibrium.

Parts per million (ppm): a ratio figure that represents the amount of one substance that is in one million parts of another substance; commonly used to describe the relative concentrations of nutrient solutions.

pH: a measurement of a nutrient solution's relative concentration of positive hydrogen ions: a pH of 7 is considered neutral; below 7 is called acidic; above 7 is called alkaline.

Photosynthesis: the formation of carbohydrates from carbon dioxide (CO2) and a source of hydrogen (H)--such as water--in chlorophyll-containing cells exposed to light involving a photochemical release of oxygen through the decomposition of water.

Pistil: the entire female section of the flower, including the eggs, ovary, style, and stigma.

Pollen: the mass of microspores in a seed plant that usually appears as a fine dust and is the agent of pollination.

Pollination: the transfer of pollen from the male part of a flower (stamen) to the female part of a flower (the style and stigma).

Reverse osmosis: the process of removing minerals from water, which is forced by pressure through a differentially permeable membrane, filtering out the minerals; can happen when growers accidentally apply too strong of a nutrient to a plant's roots, leeching life out of the plant.

Stalk: on a male flower, the portion of the stamen that supports the anther.

Stamen: the basic part of the male flower that includes the stalk (or filament), anther, and pollen.

Sterilization: the act of rendering something free from living cells. In hydroponics it is essential that all materials (especially any growing medium) used are sterile to avoid contaminating the hydroponic system. Steam and chemical agents are often used in this process.

Stigma: the surface at the end of the pistil on a female flower where pollen lands and germinates.

Style: the part of a female flower that supports the stigma.

Verticillium: any of several fungal diseases that afflict plants; commonly called wilt. See also Fusarium.

Wick: woven fiber used in some hydroponic systems to draw nutrient to a plant's roots through capillary action.

Wilt. See Fusarium and Verticillium.

Several texts were useful as resource materials while creating this glossary:

• Hydroponic Food Production, Fifth edition, by Howard M, Resh, (Woodbridge, 1997)
• Hydroponic Lettuce Production, by Dr. Lynette Morgan, (Casper Publications, 1999)
• Hydroponics Q&A, by Howard M. Resh, (Woodbridge, 1998)
• Hydroponics: A Practical Guide for the Soilless Grower, by J. Benton Jones, Jr., (St. Lucie, 1997)
• Merriam-Webster's Third New International Dictionary, Unabridged, (Merriam-Webster, 1993)

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