Hydroponics is classically defined as agriculture in water. The term is derived from the Latin hydro, meaning water and geoponics meaning the study of agriculture. Rather than using soil to grow the plants in, water is used. This may seem novel but water is the media used within plants to move nutrients (inorganic salts) and production products such as sugar and proteins (organic) from one area to another. In hydroponics, we use water to move nutrients to the plant roots to enhance plant growth.Hydroponics can only be practiced in a container. Without a container the water would be all over the floor! Being a “free spirit”, water must be contained to work. Hydroponics is all about moving water to do the work of growing the plants. A typical system consists of a reservoir and one or more containers to support the plants’ roots. The types of containers are quite variable, ranging from the standard pot to plastic pipes and eaves troughs to a sheet of plastic suspended horizontally from cables for support. It is important that containers are watertight and opaque. With water rather than soil around the roots, light must be prevented from damaging the roots. Most plants in hydroponics systems have beautiful white roots. The guiding force in hydroponics is developing a system to specifically match the crop grown. There are many types of hydroponics systems. Some are for growing long-lived plants and others for crops with a rapid turnover. Root crops can also be grown in hydroponics systems.
The simplest of systems is a modification of the self-watering houseplant pot. Rather than using soil or a soilless mix the plant is placed in a pot containing LECA (light-expanded-clay-aggregate). LECA is used because it has a very porous surface that can wick water to all areas of the pot. A wick is used in the bottom of a pot, to bring water from the reservoir to the LECA, which then provides water to the plants’ roots. The reservoir is filled as needed with a balanced nutrient source. All hydroponics systems use a water-soluble fertilizer that contains sufficient levels of nitrogen, phosphorus, and potassium for the plants. It also must contain needed micronutrients, normally provided by the soil and its microorganisms. The fertilizer can either be a prepared mix of inorganic salts or an organic tea. The problem with organic tea is that it is inconsistent in its nutrient content. It may be high in nitrogen one time and high in potassium the next, but with very hardy plants this doesn’t usually cause a problem.
Another simple hydroponics technique is `rafting’, a water culture or deep nutrient flow technique. This is usually used for commercial production of lettuce. The lettuce plants are started in a soilless mix and transplanted at six to eight weeks to floating styrofoam rafts with small holes drilled for each plant, –three or four plants to a raft. The containers consist of large troughs with a large volume of circulating nutrient mix. A pump and a reservoir can be used or a small aquarium pump will circulate the nutrient mix. The plants are placed in one end and harvested at the opposite end when the plants reach maturity. This system only works for short-lived plants, 3 to 4 months. After that period the plants may experience crown or root rot. This type of system is also called deep nutrient flow technique. In addition to nutrients the water solution must also have the proper pH (a measure of acidity) properties to allow for nutrient absorption. In the soil, factors such as soil composition and microorganisms maintain the proper pH for nutrient absorption. In hydroponics the grower is responsible for the maintenance of proper pH. To do this, dilute acids (phosphoric or nitric) or bases (potassium hydroxide) are added to the nutrient mix to maintain a pH of 5.5 to 6.5. This means the solution is more acidic than soil, which has a pH of 7, but not too acidic (vinegar is a pH of 3). In the correct range plants are able to absorb the proper mix of nutrients. If the mix is outside this range the important nutrients will not be absorbed and the plants will be malnourished.
Ebb and Flow
The most common form of hydroponics in North America is flood and drain, also known as ebb and flow. This method uses small pots with an inert aggregate such as granite (chicken grit), pea gravel, * or LECA placed in a large tray that is flooded 4 to 5 times per day. When using aggregate it is important that it be thoroughly cleaned before use. The type of crop dictates the container used. To grow an easy crop like lettuce or herbs, a simple 3 to 4 inch plastic pot can be used. For root crops a deeper pot would be needed. Beets, carrots, radishes, and most other root crops can be grown using this method. Flood and drain systems may also consist of large containers that are filled with granite. The plants are either directly seeded into the aggregate or transplanted to it. These systems work well for long-lived plants. Systems using this method can be kept for several years without any major maintenance other than monthly flushing with pH adjusted tap water to remove the build up of precipitated salts. This is a common practice with most long-lived container grown plants.
The most interesting form of hydroponics is also one of the newest, NFT, which stands for nutrient film technique. NFT systems are usually set up using troughs for containers. The tubes can be made out of hard plastic, like an eaves trough, or sheet plastic shaped into flat-bottomed tubes with support wires and clips. These can be expensive patented systems or simple ones made out of off-the-shelf white eaves troughs or white PVC water pipes. The plants are started in small cubes of rock wool, a product similar to fiberglass insulation but made from rock fiber (don’t use fiberglass insulation). The material is very porous and holds 80% of its volume in water. The plants grow in the rock wool cubes until they can be transplanted into the NFT system at the three to four leaf stage. These systems require a small pump, a reservoir, and some tubing. The nutrient mix is pumped to one end where it is allowed to flow down the pipe using gravity. At the opposite end it cascades back into the reservoir to be recycled. In these systems, the pump runs continuously and only a very thin film of nutrient flows down each pipe. The reason the thin film is necessary is to allow the roots to receive large amounts of oxygen. If the nutrient solution becomes too deep the water may stagnate and the roots of the plants starve for oxygen. Without oxygen the roots die, killing the plants. The biggest drawback of NFT systems is they can only survive for a couple of hours without the circulating pump. This means that a power failure would be fatal for the plants. Almost any plant can be grown this way except for root crops. The bigger the plant the larger the container must be, or the bigger the spacing between plants.
The newest form of hydroponics system is aero-hydroponics or just aeroponics. In these systems any container that has a lid or closed top is suitable if it has a hole for the plant and a drain hole at the bottom. Aeroponics was developed to give the roots of the plant the maximum oxygen possible. Although the leaves of a plant generate large amounts of oxygen, few plants are able to transfer that oxygen to their roots. To get oxygen the roots absorb it from the soil or water surrounding them. To increase the growth rate of plants an Israeli scientist, Dr. Hillel Soffer, developed a way of giving the roots of plants an oxygen saturated environment. Rather than the roots of the plants growing in water as with most hydroponics systems, in aeroponics the roots grow in humid air. The nutrient solution is sprayed into the container where it forms a fine mist around the roots of the plants. From the mist the plants take the oxygen they need, the water, and all the nutrients they need. There are many different systems available now and a competent craftsman can construct a simple, efficient system at home. Prairie gardeners who give hydroponics a try will find it is not a complicated process and can give enjoyment and delicious vegetables to eat.
This article is very brief, but there are many good books available on hydroponics that allow the beginner to become a proficient grower in a short period of time. Also, the Internet is full of sites that bring a wealth of knowledge to gardener’s fingertips. Unfortunately, most people still only associate hydroponics with marijuana cultivation and not with growing great tasting food and beautiful plants in their home, apartment, basement, or garden.
* Must be checked for the presence of carbonate, this can be established using the vinegar test. Add a few drops of vinegar, if the rocks foam then carbonate is present and the rocks can’t be used.
Terry Smith is owner/operator of Sunfish Consulting. His company works with industry and schools to design, build and install hydroponics and aquaponic systems. Presently Sunfish Consulting is assisting Growing Prospects Inc. of Winnipeg, Manitoba to operate a medium sized hydroponics operation producing basil and other culinary herbs for the Winnipeg area restaurants and wholesalers.