Hydroponics, simply defined, is an indoor plants soilless cultivation mode, also known as nutrient solution culture. Its core is that the plant roots are fixed in the engraftment basket and the roots sit in the nutrient solution, which substitutes for nature in providing the plant moisture content, the soil nutrients and the root-zone temperature it needs as growth factors, so the plant grows normally and completes its entire life cycle.

The crop decides the system, not the other way round. What settles the choice is how long the plant stays in the house and whether a growing medium is wanted at the roots, and everything else follows from those two answers.

The reasons for moving a crop out of soil are practical and they hold for every system on this page. Hydroponics saves management, suits different plants and is easy to operate, saves land because the crop can be planted almost anywhere, saves labour and time, saves fertilizer and saves pesticide. It gives a higher production and a higher product quality, and a more uniform product. Above all, all the growing conditions can be controlled, which is the one advantage a soil-grown crop can never offer.

That last point is also why the choice of system matters. Once the root zone is under control, the system becomes the tool that sets how that control is delivered, and the wrong tool shows up as poor aeration, salt build-up or a crop that is simply too heavy for the channels.

In commercial production, the hydroponics systems fall into NFT (Nutrient Film Technique) and substrate systems. The main difference between them is the use of a growing medium: one family runs the solution past bare roots, the other delivers it into a medium that holds the roots. A third arrangement, deep water culture, keeps the roots in a body of aerated solution instead of in a film or a medium, and it is the one usually chosen for small leafy crops where the root mass stays light.

So the working question is not which system is best, but whether the crop wants a medium at its roots. Long-cycle fruiting crops are the reason substrate systems exist; short-cycle leafy crops are the reason the no-medium systems exist.

In an NFT system the plants are grown in channels and the nutrient solution is pumped through those channels. The plant roots are kept moist by the thin film of nutrient solution as it passes by, which is the whole principle of the method: the film is deep enough to wet the roots and shallow enough to leave the upper part of the root mass in air. NFT suits shorter-term plants and crops such as vegetables and some herbs.

In deep water culture the roots hang in a tank of solution that is kept aerated, with the plants carried on a raft or in net pots through the tank lid. Because the root mass is fully submerged rather than filmed, it suits the light, short-cycle leafy crops, and it is less happy where a heavy root system would draw the oxygen down faster than it can be replaced. Both families share the same discipline: the solution has to be sampled and topped up, and the roots must never be left standing in still, warm water.

The hardware for holding a crop in these systems, such as the three tier stacking hanging basket, is a separate line from the system itself and is chosen to match the channel or raft spacing.

In a substrate system the nutrient solution is delivered to the plants through drip emitters on a timed system. The drip cycle flushes the growing medium, providing the plants with fresh nutrients, water and oxygen at every event, and between events the medium holds moisture and air at the roots. The substrate system is often used to grow long-term plants, which is exactly what the flush-and-hold cycle is designed for.

Drip is the delivery method rather than a system of its own, so on this page it is treated as the way a substrate system is fed. The components of a drip line and the way the drippers are arranged are set out on the drip hydroponic system page, and that detail is not repeated here.

Four things decide the choice in practice. The first is cycle length, because a crop that is harvested and replanted within weeks belongs in a no-medium system while a crop that stands for a season needs a medium to buffer it. The second is the weight the structure has to carry, since a substrate bed filled and saturated is far heavier per square metre than a set of channels, and that load has to be designed into the house.

The third is labour and how often a person has to touch the crop. A no-medium system repays a grower who can inspect it often, because a pump or a blocked channel is felt by the plants within hours; a substrate system is more forgiving of a missed day. The fourth is the house itself, because the same benches, channels or beds have to fit the bay widths and the working height, and the solution has to be supplied where the irrigation system can reach it.

For guidance on water and nutrient management in a controlled environment, the Food and Agriculture Organization of the United Nations publishes material for protected and soilless cropping, and commercial practice is reported by Greenhouse Grower. The company has manufactured in its own factory for above 35 years, and the equipment this page belongs to is listed under the hydroponics system range and the wider open mesh growing tray line for benches.

To settle which system suits a crop and a scale, call +86 191 5068 3942 or write to sales@cngreenhouses.com with the crop, the cycle length and the area to be planted.

Q: What is the main difference between NFT and substrate hydroponics?
The growing medium. In NFT the roots are held in a channel and wetted by a thin film of moving solution with no medium around them. In a substrate system the roots sit in a medium that is flushed on a timed drip cycle and then holds moisture and air between events.

Q: Which system suits short-cycle leafy crops?
The no-medium systems. NFT is described as suitable for shorter-term plants and crops such as vegetables and some herbs, and deep water culture suits light leafy crops where the root mass stays small. Both keep the root zone easy to inspect and quick to correct.

Q: Which system is used for long-term crops?
The substrate system, which is often used to grow long-term plants. The medium buffers water and nutrients between the timed drip events, which is what a crop that stands in the house for a full season needs.

Q: How is the nutrient solution delivered in a substrate system?
Through drip emitters on a timed system. Each drip cycle flushes the growing medium and with it brings fresh nutrients, water and oxygen to the roots, and the interval between cycles is set for the crop and the medium.

Q: Does the choice depend on the greenhouse the system goes into?
Yes, in two ways. The load matters, because a saturated substrate bed is much heavier per square metre than channels and has to be designed into the house. And the layout matters, because the benches, channels or beds have to fit the bay widths and working height.

Q: What should be sent with an enquiry about a hydroponic system?
The crop, the length of the growing cycle, the area to be planted and the greenhouse type or bay width it will go into. With those four figures the system family can be settled and the layout drawn to suit.