This is accomplished using gravity. The grow tray is placed at an angle to allow the water to flow down toward the drainpipe, and a new solution is constantly being pumped into the high end of the tube. NFT is an active system, meaning that it relies on moving parts to work. Passive systems such as Wick Systems have no moving parts. The nutrient solution flows in a thin film over the roots, ensuring that they are watered and fed but not completely soaked. The thin film ensures that the upper part of the roots will remain dry and have access to oxygen in the air. Nutrient Film Technique works best if you choose plants that do not require a lot of support—lightweight, fast-growing plants that can be harvested quickly. If you want to grow plants such as tomatoes or squash, just make sure that you have proper support systems in place such as trellises. The roots are not suspended in a growing medium in this system, so they cannot handle supporting a lot of weight from a top-heavy plant. The main components of an NFT system are the same as Ebb and Flow; the difference is their configuration.
The Grow Tray
Nutrient Film Technique uses tubes or channels instead of flat trays for the grow tray. This makes it easier to set it at an angle and to make sure that the nutrient solution flows directly to the roots without wasting any of it. Most often in do-it-yourself (DIY) systems, a round tube or PVC pipe is used, with holes drilled to fit the net pots and seedlings. This has the advantage of being cheap and readily available to the home hobbyist. The main disadvantage of using PVC as your grow tray is that the film will not evenly coat the roots. The roots in the middle would have access to a deeper depth of solution, while those closest to the edges would have only a shallow depth. This can cause uneven growth and weakness in your plants. By using a flat-bottomed channel, this problem is eliminated. Channels can also be easily built at home using simple materials such as 2×4s and waterproof plastic lining. You can either place seedlings directly into the holes of your PVC pipe or channel or, for greater stability, plant them in net pots and place the net pots in the holes. Most people do not use a growing medium with NFT, but let the roots fall directly through the net pots and onto the film. If you choose to use a growing medium, use it sparingly and make sure that the roots have plenty of room to fall through the bottom of the pot. Whichever way you choose to plant your seedlings, make sure to check and trim the roots often to prevent out-of-control growth that can clog the system. Another important consideration is the length of your grow tray. As the nutrient solution flows over the roots, it decreases in nutrient concentration and oxygen levels. Short-run trays offer an advantage over long ones because they ensure that plants at the end of the line receive a nutrient solution with the same composition as those at the beginning of the line. Long channels can be used successfully; just make sure that you regularly check the nutrient levels and pH and replenish your solution. If you notice the plants at the end of the line growing more slowly or not producing as much, consider switching to a short-run system.
The Reservoir
The reservoir is placed in the grow tray, connected to the channel by a pump on the high end and a drain tube on the low end. You must also place an air stone in the reservoir, connected to an air pump outside, to oxygenate the water. Unlike other systems, the NFT does not use an automatic timer connected to the water pump because the pump runs constantly. This can be a big problem in the case of power outages, blockages, or system failures, so make sure to check the pump and fill tube regularly and have a backup ready. One way to mitigate the risk of power failure is to use two reservoirs—one placed above the high point of the channel that feeds the solution via gravity, and another at the lowest point to collect the used solution. The spent solution can either be discarded and replaced or recycled by pumping from the low reservoir to the high reservoir. The advantage to this technique is that it doesn’t require electricity to deliver nutrition to the plants—if there is a power outage or pump malfunction, you will at least have as much time as it takes for the reservoir to empty before you need to worry about the plants suffering.
