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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.

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:

  • Coco coir is a relatively new growing medium that gives the experience of growing in soil, but many of the benefits of growing in hydro (such as faster growth and bigger harvests).
  • Soilless gardening is called hydroponics and it’s been around for thousands of years. The essential ingredient is an oxygenated mineral-nutrient solution that’s circulated through plants’ roots.
  • Expanded clay rock is an incredibly resourceful growing material, is derived from clay. Clay itself is renewable and plentiful making Expanded Clay Rock a premium growing medium due to its ecologically sustainable quality.
  • 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.
  • Rockwool. This is created by melting rock at a high temperature and then spinning it into fibers.
  • 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.

Artificial 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.

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

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.


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


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.


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 sources, 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.


The ends of a plant’s roots aren’t open-ended like a drinking straw and they definitely don'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 over-fertilizing. All plants have a different osmotic requirement or an optimum nutrient strength.

–Rob Smith


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


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


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 ofoxygen (O).

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.


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

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


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 has 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.


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 (seegermination). 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 new 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.


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.


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


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.


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!