NFT (Nutrient Film Technique) Systems
Nutrient solution flows continuously along a series of channels (eg. PVC pipe or guttering). Plant roots dangle in the flowing water and air, while the plant tops are supported above (eg. tied to trellis, ot sitting on a platform of plastic mesh). The channels are sometimes filled with coarse sand or stones, but water absorbing material such as perlite should be avoided, as it can cause root rots.
Suitable plants to grow in NFT: Tomatoes, cucumber, lettuce, beans, broccoli, cabbage, cauliflower, celery, chicory, corn, eggplant, capsicum, okra, herbs, spinich, strawberry, pepino, snapdragon, stock, chrysanthemum. Channels filled with nonabsorbant plastic beads have been very good for propagating cuttings.
Unsuitable plants: Bulbs, roses, indoor plants
Possible problems: A power failure can stop the flow of solution and result in plant death very quickly. If the series of channels are not calculated properly, some plants can end up with more or less nutrient and water than others. Solution which is exposed to light can grow green slime (ie.algae). This may not harm the plants, but it can clog up the pipes and affect flow of nutrient solution.
Gravel Bed Systems
These are a raised bed or boxed structure is filled with a coarse sand or stone (eg. Aquarium sand, washed granitic sand, blue metal chips or scoria stone). Nutrient solution can be applied various ways:
  • flooding then draining off the excess.
  • by a drip irrigation system.
  • collecting and reusing the excess or allowing it to be lost (run to waste).
Suitable plants to grow: Jerusalem artichoke, Asparagus, Garlic, Leek, Lettuce, Melons, Onions, Potato, Cabbage, Cauliflower, Broccoli, Brussels Sprouts, Pea, Radish, Tomato, Strawberry, Herbs, cut flower Bulbs, Carnation, Chrysanthemum, Pineapple,
Unsuitable plants: Root vegetables such as carrots and parsnips are more difficult.
Possible problems: If the media used is poorly drained, root rots can occur. Avoid too much vermiculite in any mix. Irrigations should not be too frequent in cool weather. (Gravel beds in Melbourne may only need winter irrigations every 1 to 4 weeks)
Rockwool slabs
Rockwool is an absorbant sponge like material, made by spinning molten rock into fine fibres. It is very light weight being made up of more than 95% air space, and having the ability to absorb and hold more nutrient solution than other materials, while still also retaining lots of air around the roots. Seeds or cuttings can be started in rockwool, and the roots simply grow amongst the fibres. Nutrient solution can be applied simply with a watering can, or through a drip irrigation system. Overwatering is almost impossible.
Suitable plants to grow: Jerusalem artichoke, Lettuce, Melons, Onions, Capsicum, Cucumber, Eggplant, Zucchini, Pumpkin, Tomato , Strawberry, Carnations, Chrysanthemum, Rose, Gerbera.
Unsuitable plants: Root crops
Possible problems: Large plants become top heavy and need trellising. Algae can grow on the rockwool surface, then die leaving a water resistant coating on the surface (avoid by keeping as much of the surface as possible protected from light; done by using wrapped slabs.
Rockwool slabs are generally not reusable.
Perlite Grobags
Commercial kits are available
Perlite in a non transparent bag, usually plastic. After wetting perlite with nutrient solution, plants can be planted direct into the media. Nutrient is applied usually through a drip irrigation system, but can also be applied manually.
Suitable plants to grow: Globe or Jerusalem artichoke, Leek, Lettuce, Tomato, Capsicum, Cucumber, Gerbera, Carnations, Chrysanthemum, most other crop plants can be grown successfully in a home situation.
Unsuitable plants: Root crops.
Possible problems: Perlite can be dusty, but wetting before use can minimize this.
Algae can grow on surfaces exposed to light. Sprinkle coarse sand on any exposed surfaces to stop.
Aeroponic Systems
Plants are supported on something like a platform or grid, with roots dangling through openings into an enclosed chamber below. Nutrient solution is periodically sprayed in the chamber to fertilize and water. Being enclosed in a chamber the humidity always remains high around the roots, preventing drying out.
Suitable plants to grow: Lettuce, tomato, parsley, silver beet, celery, cabbage, beans, strawberries, melons, cucumbers.
Unsuitable plants: Root vegetables
Possible problems: If pumps break down, roots dry out very fast
Capillary fed pots
Water and nutrients are drawn by capillary action from an outer well (eg. bucket) which is topped up as required. Example: Terracotta pot filled with gravel stood inside a bucket containing nutrient solution.
Suitable plants to grow: Many indoor plants (eg. African violet, Aphelandra, Diffenbachia, Dracaena, Ficus, Ferns, Palms etc)
Possible problems: Root rot if level of nutrient solution is kept too high, particularly in cooler weather. Allowing nutrient solution to drop too low in hot weather.
Capillary Fed Boxes
Commercial kits are often available.
These can be manual or automatic, choice of media in the box
Example of how they work: A box (often polystyree similar to what is used in a fruit shop), with a reservoir of nutrient solution in the bottom. Solution soaks up into water absorbent material which plants grow in.
Suitable plants to grow: most.
Unsuitable plants: root crops
Possible problems: Too much solution causes root rot. Some media (eg. perlite or vermiculite) can grow algae on surface.
Being a closed system, salt residues can build up (you can see this as a white cake on the surface of the media).
Nutrients are one of the most confusing aspects of hydroponic culture. There are so many to choose from, and then you could even decide to make your own. For the commercial grower, the choice of what to use can be critical. For the hobbyist though, who is using the one standard nutrient and growing a variety of different plants, any "general" properly formulated nutrient will probably work as well as another.
To achieve the ultimate with hydroponics, you need to recognize that every plant variety has different needs at each and every stage of their growth. You can cater to these needs when you grow an acre of the one crop, but if you're growing three tomato plants, six strawberries and a dozen lettuce all in the one system, you must compromise and use a fertilizer which is generally acceptable to all three plants.
Remember plants are no different in hydroponics than in soil when considering needs for light, temperature, pest control, ventilation, etc. Many people grow hydroponic gardens in small courtyards, or otherwise unused places such as along the narrow side of a house. Hydroponics can be a great, space saving way to make use of such areas; but if these areas are poorly ventilated, or are dark, then that can restrict what can be grown there.
Hydroponic beds or channels can be mounted on a wall, or set above paving, or even set up on a timber verandah. They are ideal in a greenhouse or a well lit shed, perhaps under a skylight. Many types of systems are able to be moved if you want to change the garden around, and some can even be put on wheels to allow you to move them to a better part of the garden in different seasons.
Solid Media - inert material which the plant roots grow amongst (eg. sand, perlite, rock wool, scoria, ceramic chips etc).
Automatic System - where nutrient solution is applied under water pressure automatically, using some form of irrigation system (eg. pumps)
Manual System - where nutrient solution is applied manually (eg. by lifting a container of nutrient solution above the plants and allowing gravity to apply the solution, or using capillary action, whereby the solution soaks up into the media from below the plants, via absorbent material)
Nutrient Solution - a carefully balanced mixture of nutrient fertilizers and water, which will give the plant all the nutrition it needs in the most appropriate concentration for the plants being grown.
Run to waste - where any excess nutrient is drained out of the system and lost (ie. wasted). Also called an Open System.
Closed System - where waste products cannot escape. The system is totally closed to the outside.