Analyzing Nutrient Film Technique

Indoor horticulturists are now able to choose from a number of different hydroponic systems. Each system has its own advantages and disadvantages, but all aim to produce the same result: accelerated, healthy plant growth.

A close examination of a hydroponic system is a great way for a grower to determine if that particular system is a good fit for his personal goals and physical space/environment.

By dissecting all the components that make up a nutrient film technique (NFT) hydroponic system, growers can not only gain knowledge about the way this system functions but also if, and when, NFT is a practical system for their gardening needs.

The NFT Hydroponic System

The idea behind an NFT system is to supply the plant’s roots with a continuous flow of nutrient solution through a series of trays or gutters. Some NFT systems are comprised of a single tray or gutter while others are made up of a series of each.

To create a film of nutrient solution, these systems use a pump to deliver nutrients from a reservoir to the tray or gutter located at the highest point in the system.

The trays or gutters are positioned at a slight angle to allow gravity to return the nutrient solution to the reservoir or the subsequent tray or gutter.

Although virtually any gardener can set up an NFT system, particular aspects, such as the size and shape of the trays or gutters, the pump size and location, the nutrient regimen and the particular crop should receive careful consideration. These are all pivotal factors to an NFT system’s success or failure.

NFT Trays or Gutters

The ideal NFT system uses trays or gutters with completely flat bottoms to allow for the film of nutrients to develop.

The flatter the surface, the larger surface area can be covered in a nutrient film which, in turn, gives a larger surface area for the plant’s roots to feed.

The larger the surface area of nutrient film, the larger the exposure to air around the root mass. A high air-to-nutrient ratio creates the perfect environment for stimulating root growth.

Tubes (like PVC piping) or trays with ribbed or shaped bottoms are generally not the best choices for NFT systems. The water will pool, which minimizes the surface area of the nutrient solution, thus lowering the air-to-nutrient film ratio.

NFT Pumps

The key to a properly operating NFT system is the flow of nutrient solution. To figure out what size pump is needed, the grower must first determine the necessary head height.

A pump’s head height is the maximum height to which liquid can be delivered.

For example, if a pump’s head height is four feet then it has the capability of delivering liquid four feet vertically.

Above 4 ft. and that particular pump would no longer be able to deliver liquid because the weight of the liquid itself becomes greater than the forces attempting to push it.

To determine the needed head height of the pump for an NFT system, a grower should measure vertically from where the pump will sit in the reservoir to the point of delivery.

Add about 20% to your needed head height measurement to ensure your pump will be able to do the job. It is always better to have a pump that is slightly overpowered rather than one that is underpowered.

Once you have determined the necessary head height, you can purchase a pump for your system. Because NFT systems do not require a large volume of water flow, it is best to choose the pump with a maximum head height closest to your measurement without being under.

Head height and GPH (gallons per hour) should not be confused, although as one increases, in most cases, so does the other.

Growers using NFT systems should choose the pump with the lowest GPH that still meets the minimum requirement for head height.

Once the pump has been chosen, the grower can start to modify the flow to create the perfect film in the gutters or trays.

There are a few ways a grower can control this but the easiest and most precise is to use a pump that has an adjustable flow rate.

Pumps with adjustable flow rates are perfect for NFT systems. They allow the grower to adjust the flow directly from the source—the pump.

Another effective way to control the flow in an NFT system is an inline valve connected at the point of delivery. An inline valve at the point of delivery and a pump with an adjustable flow rate are the ultimate combination for controlling the nutrient film.

Once the system is in place and the pump is adjusted, a continuous film of nutrient solution should cascade down the trays or gutters. It is important to remember that as the plants grow in the system, it may be necessary to make slight adjustments to the flow rate.

It is always good to monitor the last tray or gutter in the system to ensure it is still receiving adequate nutrient solution once the plants have become established.

NFT Reservoirs

As with any hydroponic system, the reservoir of an NFT system needs to have a consistent temperature and be well aerated.

Water chillers and submersible titanium heaters are great ways to manage temperature fluctuations in any hydroponic reservoir.

One big advantage of an NFT system is that since the nutrient solution is continuously flowing and returning to the reservoir, there is usually enough circulation to make additional aeration is unnecessary.

This is especially true in NFT systems where the return line is raised above the water’s surface in the reservoir.

As the water falls back into the reservoir it breaks up the water’s surface tension and the water becomes aerated.

To ensure their reservoirs receive maximum aeration at all times, some NFT gardeners like to add additional air via an air pump and air stones.

Harvesting from an NFT System

While other hydroponic systems are compatible with most crops, NFT systems are most compatible with vegetative crops like lettuce.

Fruiting or flowering plants, aside from a few exceptions, perform better when there isn’t constant moisture available.

This is why most commercial hydroponic tomato and pepper growers use stonewool or some other medium capable of drying completely between waterings.

Before attempting an NFT system with any fruiting or flowering plants, growers should research how compatible those plants are with that type of system.

One solution hobby growers have found is to use two hydroponic systems in the garden: one for vegetative growth and the other for fruiting or flowering.

NFT makes a great candidate for the vegetative growth as long as the plants are transplanted before the roots become entangled to the point where untangling them would cause severe stress.

For a transplant between hydroponic systems to be practical, the plant container used must be transferable between both systems.

I have seen some impressive indoor gardens where the grower used 4- or 6-in. net pots in an NFT system for vegetative growth and then transferred them into 5-gal. buckets in a deep water culture (DWC) system for fruiting or flowering.

The other consideration that should be made regarding the type of crop is the size of the plants. Lettuce and leafy greens or other plants that can be grown in a sea of green-style garden are better suited for NFT than corn, beans, tomatoes or other plants grown to larger sizes.

This is mainly because of the root mass issue associated with large plants in a NFT system.

Since the roots tend to follow the flow of the nutrients and large plants tend to have large root masses, you can imagine some of the troubles this could cause.

Intertwining of root masses is fairly normal in NFT systems, but if the plants get too large they can actually cause damage to each other and potentially clog or disrupt the flow of nutrients through the trays or gutters.

Generally speaking, it is best to avoid this method if growing ginormous plants is your goal.

The Best Nutrients for NFT Hydroponic Systems

Any soluble hydroponic nutrient regiment is compatible with an NFT system, but many NFT growers prefer nutrients that tend to leave less residue behind.

Generally speaking, the highly concentrated powder fertilizers tend to leave excess salt build-up in NFT systems and should be used with caution.

Because the roots are literally lying in the nutrient film, they are more susceptible to nutrient lockout by way of excess salt accumulation. Flushing the NFT system at transitional periods is highly recommended.

It is also wise for NFT growers to flush the system a minimum of 10 days before harvest.

Overall Advantages of NFT Hydroponic Systems

The overall advantages of NFT hydroponic systems include the efficiency of nutrient delivery, continuously available nutrition and automatic circulation and aeration of the nutrient solution.

These systems are also some of the least expensive to set up and maintain, are perfectly suited for SOG-style growing and allow for fast crop rotations.

NFT systems are easily customizable to any shape or style of garden, which means the sky is the limit when it comes to room and lighting configurations.

Overall Disadvantages of NFT Hydroponic Systems

The main disadvantage of the NFT system is the limited space for the root mass. This, in turn, limits the size of the plants that can be grown in the system. The continued delivery of moisture is advantageous during vegetative growth but can cause less-than-optimal growth for some fruiting or flowering plants.

The Future of NFT

NFT systems are still widely used by both commercial and hobbyist horticulturists. Although the commercial use of NFT is focused on leafy greens and vegetative crops, hobby growers are still discovering new ways to make NFT work for them.

Some indoor growers have had great success with NFT systems and SOG-style gardens while others use it for fast vegetative growth and then transfer the plants to a different hydroponic system for fruiting or flowering.

Whether it is used exclusively or in conjunction with another hydroponic system, it is safe to say NFT will continue to have a place in the future of hydroponics and indoor horticulture.