The nutrient film technique (NFT) is similar to the ebb and flow system in that it utilizes a pump to move nutrients in a continuous, constant flow. The difference with NFT is that the solution flows directly over the roots.
The nutrient film technique use shallow tubes that are slightly angled so that the pump moves the nutrient solution to the higher portion of the system. The nutrient solution gradually moves by gravity to the lower portion. A tube system with holes bored for the plants is used instead of trays, mainly because this system is easier to angle for proper flow over the roots.
Most horticulturalists plant directly through the holes, but it is okay to use net pots, and many horticulturalists use no planting medium (e.g., potting soil) with the nutrient film system. The roots fall through the net directly into the nutrient solution.
The nutrient solution does not completely soak the roots. The film ensures that the entire root is not submerged so the upper part of the roots remains dry.
Because it contains moving parts, NFT is considered an active system. Passive systems are those without moving parts such as wick systems, which are the simplest hydroponic systems and use a cotton wick to move the water.
The wick system is often used for teaching purposes or as a simple do-it-yourself method for home gardeners.
When using the nutrient film technique it is important to not try to grow heavy plants that require a lot of support because the roots are not in a medium that can sustain the weight of a heavy plant. It is necessary to use a self-standing trellis to support plants with heavy fruits such as tomatoes.