Articles and Information

"Methods of Hydroponic Production"

by Rebecca Nelson

Hydroponics literally means “water working” but, in practical use, it means growing plants in a nutrient solution without soil. The science of hydroponics proves that soil isn’t required for plant growth but the elements, minerals and nutrients that soil contains are. Soil is simply the holder of the nutrients, a place where the plant roots traditionally live and a base of support for the plant structure. By eliminating the soil, you eliminate soil borne disease and weeds and gain precise control over the plant’s nutritional diet. In a hydroponic solution, you provide the exact nutrients your plants need in precisely the correct ratios so they can develop stress-free, mature faster and, at harvest, are the highest quality possible.

In commercial production, the two primary growing methods are drip (also known as substrate) and NFT (Nutrient Film Technique). The are a number of variations of these methods and also several others including the float system, ebb and flow system, aquaponics, aeroponics and passive. The biggest difference between the drip and NFT systems is the use of a growing medium. In a drip system, the plant roots are in a growing medium such as perlite or rockwool and the nutrient solution is dripped onto the medium to keep it moist. In an NFT system, the plant roots are in a channel where a thin film of nutrient solution passes, keeping them moist but not water-logged.

Drip (Substrate)
The drip system is often used in commercial hydroponic facilities that grow long term crops like tomatoes, cucumbers and peppers. In this system, the nutrient solution is delivered to the plants through drip emitters on a timed system. The emitters are usually scheduled to run for approximately 10 minutes of every hour depending on the stage of development of the plant and the amount of available light. The drip cycle flushes the growing medium, providing the plants with fresh nutrients, water and oxygen.

In a commercial drip system, the plant roots are most commonly grown in a medium of perlite or rockwool. The biggest variables in a drip system are in the growing medium and the container that holds that medium. Perlite is often bagged in thin, plastic sleeves. Holes are cut in the bag and plants, usually 3-4, are set in with the roots growing down into the perlite. Recently, a bucket system has been developed to contain perlite for drip systems. Each bucket holds loose perlite and one or two plants. In either of these methods, a slot or hole is cut in the container to allow excess nutrient solution to run out. A drain line below the bag or bucket collects the excess.

Another method of a drip system that is becoming popular for lettuce and herb production is the perlite tray, usually about 24 inches wide by 10—14 feet long. An aluminum tray, coated with a non-toxic material, is filled with perlite and set on a gentle slope of 1-inch to 10-feet. The nutrient solution is continuously dripped in at the higher end of the tray and allow to trickle through the perlite to the other end. Essentially, this system is a combination of drip and NFT techniques.

In most drip systems, injectors are used to add nutrient concentrates to water when the feed cycle starts. In this case, there is no need for a large nutrient reservoir tank or the periodic dumping of used nutrient.

NFT  -  (Nutrient Film Technique)
With the NFT (also known Nutrient Film Technique) technique, the plants are grown in channels (also called gullies) which the nutrient solution is pumped through. The plant roots are kept moist by the thin film of nutrient solution as it passes by. Ideally, the bottom of the roots are exposed to the nutrient solution while the top are kept moist but not water-logged.

Most NFT channels are fed continuously at a rate of approximately 1 liter per minute. Since the plant roots are not in a growing medium, it is crucial that they are kept moist at all times. In most NFT systems, the nutrient solution is mixed in a primary reservoir, cycled through the channels and back to the reservoir. With the development of on-demand dosing equipment, a nutrient reservoir can automatically be adjusted and, with proper aeration and pH adjustment, can effortlessly be kept fresh for weeks at a time.

NFT is ideal for lettuce, leafy crops and herbs, all of which are short term crops. Larger NFT channels are used for long term crops such as tomatoes and cucumbers in many locations around the world. One great benefit of NFT, especially for leafy crops, is that with no growing medium and no soil, the crop is clean and no washing is necessary. Growers, chefs, grocers and consumers all appreciate this.

NFT channels are usually set up on waist-high stands that slope slightly to allow the nutrient solution to drain to one end. Although round pipes have been used in NFT production, most growers have found flat bottomed channels or gullies provide greater surface area for root development and oxygen uptake, resulting in better, faster plant development.

Float
Float systems take advantage the surface of the nutrient solution. Most float systems are long, rectangular reservoirs built out of cement or wood and lined with a durable, poly liner. Holes are cut in a foam board which floats on the surface of the water and plants in net pots are set in the holes. The plant roots dangle in heavily aerated nutrient solution.

In areas where raw materials are limited and manufactured hydroponic systems and components are not available, the float system can be an economical means of hydroponic crop production.

Ebb and Flow
The Ebb and Flow (also know as flood and drain) method of hydroponics simply floods a growing area for 5 or 10 minutes and then the nutrient solution drains away. The nutrient solution is stored in a reservoir that can be located under the grow table. Ebb and Flow is common in hobby systems but not often found in commercial production. In an Ebb and Flow system, the plant roots are usually grown in a medium of perlite, rockwool or expanded clay pebbles.

Aquaponics
In hydroponics, you mix a specific nutrient formula in solution which is fed to the plants. In aquaponics, you combine aquaculture (fish farming) with hydroponic production. The nutrient-rich waste water from the fish tanks is pumped through plant grow beds. Although not as precise as a hydroponic fertilizer mix, the effluent from a fish tank is high in nitrogen and many other elements and most plants will do quite well in aquaponics.

The key to aquaponics is the establishment of a healthy bacteria population. Beneficial bacteria that naturally occur in the soil, air and water convert ammonia (the primary form of fish waste) to nitrate and then to nitrate, which the plants readily uptake. In consuming the nitrate and other nutrients in an aquaponic system, the plants help to purify the water.

Although the combination of hydroponics and aquaculture is quite new, the interest in this technology is booming. Aquaculturists who normally have to buy expensive water purification equipment to purify the water see aquaponics as a great way to clean the water and end up with another, very marketable crop. Hydroponic growers see the value in a natural source of nutrients, already in solution.

The water from a fish tank can be pumped through any hydroponic grow bed in place of a hydroponic fertilizer solution. For commercial aquaponic production, designs that show great promise include the float system, NFT and ebb and flow.

Aeroponics

Aeroponics is the method of growing where the plant roots are constantly misted with a nutrient solution. Designs include an A-frame with boards on each side, plant plugs set in each side and a mister between the boards spraying the roots. A round, large diameter PVC pipe set vertically with plant plugs all they way around and a mister mounted inside is another way to set up an aeroponic system. Although aeroponics is a unique way of growing, it is not a common means of commercial production.

Passive

Passive hydroponic systems are sometimes used by hobbyists. A passive system does not use pumps or timers to flood the root zone. The roots usually dangle into the nutrient solution and draw what they need. A passive system is generally slower growing and not as productive as the other methods discussed.