Hydroponics is simply growing plants without soil. If you can imagine a way to grow a plant sans soil, you have thought up a hydroponic system. That said, there are a number of hydroponic systems that have emerged as standards with countless variations emerging from them. I’ll discuss some of the common uses of those systems in both small and commercial settings, and discuss some of each types advantages.
1. Media Culture with overhead watering
Perhaps the most common hydroponic system. Many people (unknowingly) have a hydroponic plant growing in soilless media (that looks like soil). Often these plants have a slow release fertilizer so that the caretaker does not have to add nutrient via the water.
Many bedding plant and perennial greenhouses also grow their products this way, with a person watering the plants from above. Bedding plant, potted plant and perennial places, in particular, use this method when they want to use technical, exact watering methods to keep plants short. Why would a grower want to keep their plants short? Because in shipping plants being able to stack the semi-truck 7 plants high or 6 makes a huge difference in an industry with tiny margins.
The easier way to keep plants compact is through growth (retarding) hormones, but if you’ve ever bought a plant that sits in your garden without growing, it’s probably because of those hormones. The best growers use water for the same purpose, as keeping the plants at an exact moisture level will encourage compact growth.
In professional greenhouses where cuttings are taken, plants are often also watered overhead by misters while the roots are developing.
One of the primary advantages of this system is that it takes very little infrastructure to set up (it’s inexpensive). It also relies on the waterer to be very observant if watering is to be done technically as it’s easy to give too much or too little. As with all media systems, it is very robust to power outages and interruptions in the machines because the media states moist enough for a long time after the misting is done.
It’s a challenge, though, to water well and it requires a lot of labour. Overhead watering also looses more moisture to evaporation and puts the plants at a significantly higher risk of disease (as most pathogens can only infect a plant while moisture is present).
2. Media Culture with drip irrigation
Although uncommon in houses, many patio watering systems use drip irrigation. Generally each plant has one emitter at it’s base and the water is either on a timer or manually turned on.
We water our tomatoes, eggplant, cucumbers and some smaller crops using drip systems in the greenhouse, and this is probably the most common way to grow large, long-term fruiting crops. Our system is triggered by light levels (we have a computer that calculates how long various intensities of light are coming into the greenhouse and triggers an irrigation event when certain thresholds are passed). The fancier system is to employ special scales that use weight to identify how moist a plant is. These are distributed through the greenhouse and the computer uses the assumption that all of the plants in the same area are about equally dry, and it waters whenever the sensors indicate.
Hanging pot growers often water in a similar way with a weighted dripper in each pot. These often use timer or light-sensing algorithms to determine when to irrigate.
This, system is superior to overhead watering in that it does not moisten the leaves (reducing disease pressure) and because it is easy to automate. It is also very easy to measure exactly how much moisture is being used because the emitters are calibrated to release specific amounts of water.
Drip irrigation would be difficult to set up in a house, because it requires a lot of ugly, expensive infrastructure. It works best where one has many plants in a concentrated area, and where precision is a dominant requirement. It also requires a good pump, filters, and pressure-compensating emitters to work reliably, which is pricy.
3. Media Culture with wick irrigation
In this method, two pots are used. One that holds the growing media, and a second, below it, holding the nutrient-rich water. A wick connects the two pots in such a way that it can soak up water from the lower pot and transfer that moisture to the media-holding pot. There are many commercially-made pots that use this method, and it is simple to build a home-made wick system.
I think that this is the best way to keep a houseplant well-watered. It reduces labour (you only have to water it occasionally), requires minimal infrastructure, does not wet the plant leaves, and makes allowances for those of us who occasionally forget to water our plants. It is important, with this system, to occasionally water from above to wash away salts that may have built up in the root zone.
I don’t know of anyone using this system in a commercial setting, so if you know of one, please write a comment about it below!
4. Nutrient Film Technique (NFT)
Plants are grown in troughs (often similar to rain gutters). The nutrient solution runs along the trough and the plant roots are suspended into the trough allowing the lower roots exposure to the solution and the upper roots collect air. Since the plants do not have a media for the roots, they need extra supports to be held upright and the root zone should be enclosed (usually with plastic) so that the relative humidity around the roots remains stable at 100%.
This system was, at one time, quite commonly used for large, fruiting crops. Now, however, they are more common for small-stature, vegetative crops such as herbs and lettuces. NFT is particularly common in Australian lettuce production.
Plants respond well to this growing system and grow quickly. It’s particularly suited to plants that grow for a short time as after about 3 months roots tend to block water and create low oxygen areas that will kill the roots and the plants begin to struggle.
Probably the primary reason that this system is not used in many commercial settings is that power outages or mechanical problems can damage the plants in short order. This requires that a serious grower has redundant machines plumbed in with backup systems on standby.
Also, NFT has a lot of water moving all of the time so a good filtration system is required to capture the water for reuse.
4.5 Modified NFT systems
There are several ways that people have modified NFT. I will summarize the most common.
(a) Adding very coarse media (such as crushed rock). This way there is still a very thin layer of water flowing down the channel, but it has to flow around the large rocks in the pathway.
(b) Adding another (or several) layers of channel so that the roots take longer to get to the point of blocking water and plants may be grown in it longer.
(c) Using a deep, flowing water that is aerated instead of a film of water. A cross between deep water culture and NFT.
5. Ebb and flow (aka flood irrigation)
Plants are grown in periodically flooded containers and then almost immediately drained. There is usually some sort of coarse media (such as gravel, clay pellets, or stone though many substrates could be used).
Commercially, young plants (such as tomatoes or cucumbers) are commonly raised this way before they go to the main house. Likewise it is used by some perennial, potted plant and bedding plant producers. In many cases, they are often raised on flood floors which are concrete floors that flood and drain periodically.
There are also flood and drain benchtops available for greenhouse production, though these are more commonly used with potted plant growers than for young plants.
This is a system that is often used together with small aquaponic systems. It is good for this in that it is relatively simple to set up, and there are fewer small parts that will get plugged by the fish effluent.
Also, it uses coarse media, so it has more capacity to hold moisture than NFT or aeroponics (if the power goes out/pump fails this will last longer). As with most hydroponic systems, it is a sub-irrigation method (water comes from below and does not touch the leaves) which means less disease issues.
Flood and drain requires a moderate amount of infrastructure which can be pricy; it recirculates water so some filtration is helpful if one has a long-term crop.
6. Float Culture (aka Deep Water Culture, DWC)
Plants are planted into trays (usually styrofoam or plastic) that float on the water. The roots hang down into the water which is heavily aerated (to avoid drowning).
Commercial systems can be very elaborate, but essentially work in the same way as simple systems. Commercially this is used mostly for lettuce and herbs, and also for tobacco seedlings before they are planted out to the field. Usually, commercial systems take up a large greenhouse space with just a small isle all the way around it. This is because the plants floating on the water have little friction and can be moved easily from one end to the other. In a simple system, the plants are planted on one side of the grow space and moved towards the other (harvest) side each week.
The big advantage of deep water culture is that it uses space very efficiently because there are so few isles. It also uses no overhead watering (reducing disease pressure), can be quite inexpensive to set up, and grows plants quickly.
As with NFT, plants older than 3 months tend to develop root problems, so this is primarily used for short-term crops. Also, deep water culture requires good aeration which means infrastructure and air pumps. The system is alright in a power outage for a few hours, although there is a linear relationship between good aeration of the water and the speed that the plants will grow.
Plants are planted with the roots hanging into an air space. Nutrient-rich water is sprayed into the rootzone keeping the roots moist, but aeration is not an issue. Excess water is usually collected back into the main container.
This is a popular system among hobbyists, but uncommon in commercial settings. It is the only method listed here that I”ve never tried before, so I’ll have to give it a shot soon.
I understand that this system promotes particularly fast growth of plants—I assume that this is because of the fantastic ability of the roots to get enough oxygen. It is also a system that can work well in vertical walls and similar set-ups.
This is, however, quite an expensive system to set up and operate. It is very susceptible to problems if the power fails (and the misters stop). Since it is less commonly used, there is less knowledge of how to do this well. Because of it’s reputed fast growth, though, I suspect it will make a bigger impact in the future.
This is a variation of hydroponics that can use any of the growing methods listed above, its difference is in how the nutrients are maintained in the system not in how the plants are put into the system.
It works like this: fish are grown in ponds. Their water is circulated out of the pond, often filtered, then put into the plant zone. The plants take the nutrients out of the water (which happen to be toxins to the fish), cleaning the water for the fish.
The plants can be grown using any other hydroponic method (I’ve seen DWC, NFT, drip irrigation and flood and drain systems in operation).
It’s a fantastic system, but needs a lot more management than other hydroponic systems. Also, it is a system that tends to be challenging in power outages because the fish need constant oxygen, and in order to provide enough nutrient for the plants the fish have to be grown in concentrated groups.
There are numerous hydroponic systems and even more considerations when choosing one. When choosing, make sure to take into account what you will do when a machine breaks or the power goes out in the middle of the night, or when you’re away. That said, if you’re as geeky as me, you’ll find it interesting to try all of these methods regardless of how challenging they are to use.
Case in point–in our greenhouse, we use drip irrigation and float culture extensively, but also have some homemade flood tables and use overhead watering in a few places.
Please write a comment below about what systems you’ve used and what challenges and successes you’ve had with them.