Hydroponics Guides

Hydroponics is the growing of plants without soil. A variety of techniques exist.

Researchers of plant metabolism have discovered that plants absorb nutrients as simple ions in water. In natural conditions, soil acts as a nutrient reservoir but the soil itself is not essential to plant growth. When the nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive. Almost any plant will grow with hydroponics, but some will do better than others. It is also very easy to do; the activity is often undertaken by very young children with such plants as watercress.

There are a variety of techniques employed in hydroponics. Some, while dispensing with soil, use relatively inert material as a physical support for the plant roots. Other techniques dispense altogether with any growing medium, delivering nutrient solution directly to the roots by a variety of methods.

Passive hydroponics

The simplest method: the plant is planted in a container (pot or bag) of growing medium, and the container stands in a tray of nutrient solution. The medium generally has large air spaces, allowing ample oxygen to the roots, while capillary action delivers water and nutrients to the roots. A variety of materials can be used for the medium: vermiculite, perlite, clay granules, rockwool, gravel, Oasis Horticubes. Some newer media that are becoming popular are coir fibre, and cocoa bean shells. This needs the least maintenance of all hydroponic methods, requiring only topup and occasional replacement of the nutrient solution. This keeps the medium regularly flushed with nutrient and air. It is important in passive hydroponics to wash out the system from time to time to remove salt build up. This may be checked with a PPM meter, a good average reading would be about 1500 PPM. Lettuce grows well at about 800 PPM and tomatoes to 3000 PPM but both will grow reasonably well on 1500 PPM. It is important to keep the pH reading at about 6.3 to enable nutrient uptake. Data are available for the optimum settings for most plants. This is commonly employed for large display plants in public buildings: in Europe a system using small clay granules is marketed for growing houseplants.

Passive hydroponic at home - Semi-hydroponic for growing orchids

Flood and Drain (or Ebb and Flow)

In its simplest form, there is a tray above a reservoir of nutrient solution. The tray is either filled with growing medium (clay granules being the most common) and planted directly, or pots of medium stand in the tray. At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient, after which the nutrient drains back down into the reservoir. This keeps the medium regularly flushed with nutrient and air.

Deep Water Culture (DWC)

Deep Water Culture is a hydroponic method of growing plants in which the roots are suspended above, and allowed to drop down into an aerated nutrient solution. This is not natural but with a properly aerated solution the roots can be continually submerged without problems because the roots take up nutrients in the presence of oxygen. The solution is usually aerated constantly by using standard aquarium pumps and air stones, which deliver oxygen to the roots. The container holding the roots and aerated nutrient solution must be completely light proof in order to prevent algae growth. The solution must be topped off from time to time.

Drip feeding

Similar to Flood and Drain in its physical setup, except the pump delivers a continuous trickle of nutrients and water onto the medium. The emitters are commonly set to run 5 to 10 minutes every hour.

Wick feeding

A variation on Drip feeding, except that the plant draws water by means of a wick. The wick runs from the base of the plant container (e.g. a pot or a tray) down to a bottle of nutrient feed solution. The solution travels up the wick into the plant through capillary action.

Raft cultivation

A variant of DWC sometimes used for lettuces: sheets of expanded polystyrene have holes drilled through them, and young plants are placed in the holes with the roots hanging down. The sheet then floats in a shallow tank of nutrient solution.

Nutrient film technique (NFT)

In this method, the plants grow through light-proof plastic films placed over shallow, gently sloping channels. A steady flow of nutrients is maintained along the channel, and the roots grow into dense mats, with a thin film of nutrient passing over them (hence the name of the technique).

A downside of the technique is that it has very little buffering against interruptions in the flow e.g. power outages, but overall, it is probably one of the more productive techniques.

Aeroponics

A class of hydroponics where the roots of a plant are suspended in a mist or fog of nutrient rich solution. Traditional aeroponic techniques use pumps and misters more commonly found in micro-irrigation systems, whereas state-of-the-art techniques employ ultrasonic nebulizers which render the nutrient solution into an extremely fine fog.

One of the most obvious decisions a hydroponicist has to make is which medium they should use. Different media are appropriate for different growing techniques.

Expanded Clay

Also known as 'hydroton' or 'leca' (=light expanded clay aggregate), trademarked names, these small round baked spheres of clay are inert and are suitable for hydroponic systems in which all the nutrients are carefully controlled in the water. Clay pebbles can be reused provided they are cleaned thoroughly between crops. Baked clay pebbles are highly porous, yet irregularly shaped to create an balance of air space and nutrient solution.

Rockwool

Rockwool is probably the most widely used medium in Hydroponics. Made from basalt rock it is heat-treated at high temperatures then spun back together like candy floss. It comes in lots of different forms including cubes, blocks, slabs and granulated or flock. When medium is dry, care needs to be taken so as not inhale any particles. Inhaling such particles may carry a health risk.

Coco Coir

Coco is a compressed medium created from the husks of coconuts. Coco coir comes also in bags and in slabs. Some types of Coco coir are very high in sodium (salt) due to the nature of Coconut Palms growing on island environments and being processed in the salt air.

Perlite

Perlite is a volcanic rock that has been superheated into very lightweight expanded glass pebbles. It is used loose or in plastic sleeves immersed in the water. It is also used in potting soil mixes to decrease soil density. Perlite has similar properties and uses to vermiculite but generally holds more air and less water.

Vermiculite

Like perlite, vermiculite is another mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surrounds the plants roots, it's possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

Oasis Root Cubes

An open cell foam cube with a preset pH and a mild fertilizer added, Oasis root cubes produced by Smithers Oasis (external) is the choice of large scale nutrient film growers. It is available in many different sizes. Widely marketed in sheets sized to fit commercial trays (10"x20"), it is a convenient propagation media. Each sheet is pre-scored for easy removal of a single cube, block of cubes, or strip of cubes. Each cube has been pre-punched with a dibble hole for quick and easy seed or plant cutting insertion.