Nutrient Film Technique (NFT) systems are used widely by both commercial growers and hobbyists worldwide. They are renowned for being low maintenance and producing fast growth. By following some basic principles, anyone can achieve superlative results using NFT systems. Following on our introduction to NFT Gro-Tanks in Issue 9, Gareth Hopcroft takes us through how to set up and maintain this popular hobby system. After all, a picture of a cucumber-laden vine is worth a thousand words!

The basics – What is NFT?

NFT stands for Nutrient Film Technique. With this hydroponic system, plants grow in a purpose-built sloping channel with a fall of 1:40–1:50. Nutrient solution is pumped from a reservoir onto the channel where it passes over the plants’ roots and finally returns back to the reservoir. The roots on the channel develop to form a mat, which is partially in the shallow film of re-circulated nutrient solution, and partially above it. Utilizing this technique, the root mat growing in the nutrient film is supplied with essential water and nutrients, and the root mat above the film remain sufficiently moist with an abundance of oxygen.

The NFT system was developed between the 1960s and ’70s by Dr. Allen Cooper at the Glasshouse Crops Institute in the UK. In the early days, the growing channels were made in concrete floors. Today, growing channels are made from plastic and are often referred to as “trays” or “gullies.”

Why choose NFT?

Other than supplying your plants with the ideal root environment, NFT systems are incredibly efficient and environmentally friendly. The nutrient solution is recirculated for long periods: in some commercial applications, for many months. This continual recycling of the solution makes the most out of the water and nutrients you’re supplying. NFT systems also use very little growing media: just the small amount of substrate the plant is propagated in. This means that after each crop all you have to dispose of is a mat of roots, which easily biodegrades.

NFT Gro-Tanks

The system I will be demonstrating is called a Gro-Tank and is manufactured in the UK by Nutriculture.

The Gro-Tank is great for small-scale production as it has a wide top tray for the roots to grow on, with the reservoir directly beneath it spanning its whole length. A small submersible pump in the reservoir delivers nutrient solution to the tray above, which flows down the tray and back into the reservoir. This compact, self-contained design eliminates the need for lots of pipe work and is very low to the floor, making best use of the height available for tall/vining plants.

I have used the Gro-Tanks for many types of crops, including lettuce, basil, watercress, coriander, parsley, rocket, chard, chives, tomatoes, peppers, chillies, strawberries, cantaloupe melons, cape gooseberries, and many more. The diary below shows one of my NFT grows with cucumbers. I hope you enjoy…

Equipment

1 x heated greenhouse
1 x heated propagator
5 x starter plugs
5 x 4” rockwool blocks
1 x 604 Nutriculture Gro-Tank: 5ft x 1.5ft (153cm x 49cm) tray with 16 gallon (60L) reservior
1 x submersible adjustable pump
1 x submersible water heater
Spreader mat (capillary matting)
4 x roller hooks (plant supports)
Vine clips
Liquid nutrients and growth supplements

January 18th – Germination

I’m growing a cucumber variety called Carmen, which is an all-female F1 hybrid variety. The majority of cucumber varieties produce both male and female flowers; all we are interested in are the female flowers, as these develop cucumber fruit. This all-female (parthenocarpic) variety will develop a seedless fruit without the need for pollination. I found Carmen great last year for greenhouse growing as you don’t have to pick male flowers off and it produces large, full fruits.

I planted the seeds in starter plugs pre-soaked with a low-strength nutrient solution (EC 1.2) designed for seedlings and cuttings, and a liquid beneficial microbe additive. These were placed in a heated propagator and germination was fast!

Shown here is one cucumber seedling 8 days after planting. At this point they were transplanted into 4” rockwool blocks.

January 31st – Propagation

Considering it’s been 21 days since I planted the seeds, I’m happy with the way they’re progressing. They are now being watered with nutrient solution (EC 1.4, pH 5.8) every 2-3 days. The roots are doing really well and can be seen on the top of the block.

Without the block covers, algae would be taking over and the roots would not be growing so well on the surface. The natural light entering the greenhouse is being supplemented with 220W fluorescent strip lights. These plants should be ready for their NFT system in about 1 week.

February 4th – Growing on

The plants now need nutrient solution every day and the roots are clearly visible all over the bottom of the block. I also have increased the EC to 1.6. They will need to be planted in the next few days.

February 5th – Setting up

These cucumber plants are now 26 days old and are ready to go onto their final system, which will be an NFT Gro-Tank.

The most important thing about getting plants ready for NFT systems is to ensure they are well-established and have a mass of healthy white roots. Without this mass of roots inside the rockwool block, the plant will not be able to cope with the continuous irrigation of the NFT system. These plants have been propagated using an air pruning technique (see “Power Propagation” UGM0005) to ensure the rockwool block is packed full of roots.

This is the Gro-tank I will be using (below). It is called a 604. Nutriculture, which makes the system, also makes 5 other size variations to suit any grow area. The top tray is where the plants are placed and the reservoir underneath stores 16 gallons (60L) of nutrient solution.

The Gro-Tank has one delivery tube where the nutrient solution is pumped onto the tray using a small submersible pump with an adjustable output:

To ensure an even distribution of nutrient solution on the tray, I use capillary matting, aka “spreader mat.” The system manufacturers recommend using spreader mat and supply it with the system. One layer is enough. After laying it out, I fill the reservoir with water that has been standing in a storage tank for a few days: this allows some chlorine to be evaporated and, more importantly, allows the temperature to rise. Tap water in February in the North of England usually comes out ice cold and will seriously stress plants if used.

Once the tank is filled I turned the pump on and slow the output down so the solution lands in the middle of the first diamond. This provides a flow rate of approximately 1 quart (1L) per minute. Recommended flow rate for NFT systems can be anywhere between 13.5oz to 2 quarts (400ml to 2L) per minute. Determining flow rate in NFT systems usually depends on channel length; if you have very long channel lengths you will need larger flow rates. You could probably write a thesis on other variables that will determine the required flow rate for NFT, but I find that as long as nutrient solution flows as a shallow film and does not “puddle,” the plants grow well.

After a few minutes of the pump running, the spreader mat wets throughout the tray. I always run the pump and observe the way the water is flowing down the tray. I have found from experience that if the Gro-Tank is not placed on a level floor then some areas of the tray will develop puddles and other parts will remain dry. Leveling out the tank with thin pieces of plywood usually sorts out an uneven floor. Luckily, the floor is fine and I’m happy to “go with the flow.”

Now that I know the flow down the tray is perfect, I cut out the planting holes in the corriboard cover. Corriboard is twin-walled, semi-rigid plastic sheeting. It prevents any light from reaching the roots and can help provide a bit of support for the plants. I’m planting 4 plants in the Gro-Tank, so I cut the holes accordingly.

Providing support for large plants is very important. To support my cucumber plants I use roller hooks, which are a spool of string on a wheel attached to a support hook. The vines are trained up the string with the help of plastic vine clips. When they grow tall enough to reach the wheel, string is let out, which lowers the vine. This support hook is then moved along so the excess vine at the bottom rests on the corriboard. Using this technique, one of my cucumber plants last year was 49 feet (15m) long!

Another popular way to support plants on NFT systems is using netting, which is stretched out horizontally on a frame above the plants so that when they grow into it they are supported by the net.

Before planting onto the tray I remove the plastic wrapper from around the block. When I was learning how to grow using NFT systems I was told by a more experience grower at the time to “leave the wrapper on, otherwise the block will fall apart.” After a few crops I decided to experiment so I slid the wrapper up the block exposing the bottom third. This helped with initial establishment and root growth from the block, which I believed was a factor in achieving a more successful crop. The next crop I decided to risk it and remove the wrapper completely and, instead of the block falling apart, I got quicker establishment and a much better root mat. The block lasted the whole season, staying completely intact. Not surprisingly, I don’t follow this grower’s advice anymore.

Once the roller hooks are in place, I tie the string around the rockwool blocks and place them into position:

The positioning of the blocks on the tray is fairly important: I find staggering the plants works best. This allows the nutrient solution to flow uninterrupted through the mid-section of the tray, which helps once the root mat has built up. I also find that positioning the blocks so that the solution can flow through the grooves on the bottom of the block helps with establishment.

Then I place the corriboard and black and white sheeting back on the tray and lower the plants into their pre-cut holes. I cut the black and white with an X so the folds can be repositioned over the top of the block to cover it and prevent algae growth.

Now that the plants are in their system, I add a “grow” nutrient to the water in the reservoir at an EC of 1.6 and a pH of 5.8. I also add a strong dose of beneficial microbes to the mix to aid with root growth and disease prevention.

I put a submersible water heater in the tank and set the thermostat to 64°F (18°C). I also plugged in the pump, which I will now leave alone to run 24/7. Some growers plug their NFT pumps into a segmental or interval timer. This “pulse feeding” is not the strategy Dr. Allen Cooper conceived when he developed NFT, but some people growing plants with more sensitive root systems or who use large propagation blocks find it helps. It’s very important when implementing pulse feeding that the root mat never approaches a dry state. I have contacted Nutriculture about pulse feeding, and they only recommend that the pump is run 24/7.

These cucumber plants should settle in and start growing vigorously in the next few days. Hopefully I should be picking my first fruits in no time.

February 14th – Vegetative Progress

In 11 days these cucumbers on the NFT Gro-Tank have more than doubled in height and they are establishing well into their system. I have attached them to the string using plastic vine clips, which clip onto the string and hold the vine in place.

I have been routinely checking the nutrient solution pH and EC every 1-2 days. The pH was rising by 0.2 points every 2-3 days. As the pH reached 6.2-6.4, I added phosphoric acid to bring it back to 5.6-5.8. I like to let the pH drift a bit rather than keeping it within a tight range: as long as it doesn’t go higher than 6.5 or lower than 5.5, I’m not worried.

Usually I find the nutrient strength stays stable or increases slightly as the water level drops, but over the past 11 days the plants have used approximately 4 gallons (15L) of nutrient solution and the EC has dropped to 1.2. This is an indication that the plants are hungry, so I top up the reservoir with water and increase the nutrient strength to an EC of 1.8. Whenever I add anything to the tank I disconnect the delivery tube from the tray and submerse a larger 265 gallons/hour (1000L/hour) pump in the reservoir to mix the solution. Once the nutrient solution is corrected, I reconnect the delivery tube.

I always estimate how much water I add back to the tank and take a mental note. Once I know I’ve added back roughly the same volume as the tank holds (16 gallons / 60L) I will consider running the reservoir down to half full, emptying the tank, and refilling it with fresh water and nutrient solution.

Many growers change out the nutrient solution every week, regardless of how much the plants are using. I find this a bit unnecessary and like to base my solution change-outs on how the plants are using it.

The pictures below show how well the roots are extending from the rockwool blocks. Soon there will be a thick mat of roots all over the tray:

February 25th – Flowers and Fruits

It always amazes me how fast plants grow in a productive environment using hydroponic systems, but cucumbers are a whole other ball game. In 11 days they have more than tripled in size and burst into flower. One fruit is already quiet large and will be ready in a few days.

They have also started sending out tendrils and growing side shoots. I remove both but keep a few side shoots for cutting material and put them in my aeroponic propagator.

The greenhouse environment is pretty easy to maintain this time of year. The heating keeps the night-time temperature around 64°F (18°C) and the top vents ensure the day temp does not exceed 77°F (25°C). I have 2 centrifugal humidifiers running to keep the relative humidity between 60-70%.

The plants are now using 1.5-2 gallons (6-8L) of nutrient solution per day and I make sure I top up the reservoir frequently. It’s better to have a full tank as it provides a better buffer for changes in pH and EC. The plants seem happy with the nutrients at 1.8 EC so I’ll leave things be.

One thing I love about NFT is that you don’t have to think about irrigations. The pump is on a slow trickle, and that’s all that matters.

The cucumber fruit develops behind the un-pollinated female flower.

February 27th – Nutrient tweaking

We have had a few warmer, brighter days recently and the plants are loving it. The first large fruit is growing well but is showing signs that I need to tweak the nutrient slightly. You may notice in the picture below that the bottom of the cucumber is slightly more bulbous than the top. The leaves of the plants are also showing a faint yellowing (chlorosis) around the edges. This is a sign that the plant requires more potassium.

To increase the potassium in the solution I add a blooming additive high in potassium and phosphorus at the rate of 1 ml per L. Before adding this I top up the tank with water, add the PK booster, then add more base nutrient to bring it back to 1.8.

You may also notice some loose vermiculite on the tank and floor. I have introduced the predatory insects Phytoseiulus persimilis, which come in a vermiculite carrier. I noticed a small outbreak of spider mite on some peppers on the other side of the greenhouse, so as a precaution I sprayed all the plants in the greenhouse with a natural-contact insecticide that works by suffocation, not chemicals. A few days after spraying, I introduced the predators to clean up any lingering spider mites. I will now introduce a bottle of 2000 Phytoseiulus persimilis every 4 weeks throughout the greenhouse and keep spraying to a minimum.

February 29th – Roots going mad

The roots are really growing well now and starting to develop to form a mat in places. I like to regularly inspect the roots in the NFT system, mainly because you don’t get to do it with other systems!

March 3rd – Plant Training

The plants have now reached the full height of the greenhouse so I let out a small amount of string and lower the vines.

Once I have lowered these a few times I will move the roller hooks clockwise around the Gro-Tank. The stems rest on top of the corriboard. I started using this training technique with my tomatoes and tried it with cucumbers. I find it works pretty well but most commercial growers implement an umbrella training system. I have yet to try it but will get around to it one day.

March 11th – New plants!

The side shoots I took off 2 weeks ago are now rooted plants and are ready for transplanting.

I have to say, aeroponic propagators are great. I have one running continuously in the corner of my greenhouse and just put shoots in and forget about them. 1-2 weeks later you have cuttings. Can’t get any easier.

March 14th – The Bumper Crop

The plants have definitely responded well to the PK booster. The leaves are now dark green all over and the fruits have developed to be large, full and evenly shaped. Some are slightly curved but it adds to the character!

I’ve had 3 cucumbers off the plants so far, but today I picked 6 ripe fruits in one go. From here on out I guarantee I will have so many cucumbers that I will make myself and all my friends sick of the sight of them!

March 26th – Growing on

The cucumbers have been growing well and are now producing ripe fruit at a steady rate of two to three cucumbers every four days. They could try and produce more but I remove developing fruits once there are more than 4 developing on each vine. If there is a high fruit load on the plant, developing fruits will abort. The weather is starting to warm up and the greenhouse is now thriving from the increased day lengths and light intensity. Bring on summer!

Looking Ahead

Recognizing the environmental conditions and adjusting the nutrient solution is part of my ongoing management strategy for recirculating systems. As warmer weather comes along in May and June I will certainly see the EC rising every few days in the reservoir. As this starts to happen I will dilute the EC slightly to around 1.6.to compensate.

Water uptake will certainly go up too so I will have to make sure I regularly top up the reservoir once a day. I also make sure I service my pump every 2 months. This is fairly quick and easy to do and will give me peace of mind that it’s in good working order.

Interested in NFT and want to learn more? If you missed Everest’s introduction to NFT and grower’s tips in UGM0009, check it out here!