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Running Solutions in NFT |
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| Everything you could ever want to know about NFT all condensed into one article (OK maybe not everything, but most of the basics!). Includes a look at temperatures, aeration, solution changes and pH adjustment. |
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Running Solutions in NFT
In NFT (Nutrient Film Technique), a thin film of nutrient solution runs down a channel or gully and plants are placed into this flow of nutrient in rockwool cubes or net baskets. Once in the system the roots can grow in the open channel getting all the water, nutrients and oxygen they need. The nutrient is usually re-circulated from a main reservoir.
Commercial use of NFT is a major producer of staple food crops around the world for reasons varying from water conservation to a generally better quality end product. In the indoor hobby world and in greenhouses NFT is also very popular and there are a range of systems like the NFT Gro-Tank on the market suited to small scale set ups.
In a typical system the nutrient solution is pumped from a main nutrient reservoir, through a channel or gully where the plants are located and out the other end and back into the main reservoir. This is what is referred to as a re-circulating system. Plants are started in rockwool cubes or net pots and are then placed directly into the flow of nutrient in your gully or channel. Once in the system the roots can grow in the open channel getting all the water, nutrients and oxygen they need. The root zone should be covered to protect it from light and heat as well as encouraging good root growth into the channel. Spreader mat should be used one layer thick on all wide channels to help spread the water evenly across the whole channel.
The abundant amount of water and oxygen to the root zone makes this system very good for excellent growth rates and also helps the plants to cope with very demanding light conditions. Because of the semi-exposed root zone this makes room temperature and more importantly nutrient solution temperature much more crucial than in other types of system. Growth rates and even plant health can be seriously affected if the roots get too cool during lights off or too warm during lights on.
One big advantage with this type of system is the lack of media especially when it comes to clean up between crops.
Temperatures
The ideal nutrient solution temperature is about 21oC. At this temperature the water is warm enough to stimulate good growth rates but at the same time cool enough to carry maximum oxygen content. The warmer the solution gets the less oxygen it can carry, and under optimum light conditions it is essential that optimum oxygen content is also maintained. Try and keep this nutrient temperature constant day and night, winter and summer. Heavy Duty Hydor Nutrient solution heaters are available to help keep temperatures constant whilst thermometers and digital nutrient temperature monitors are also available for regular monitoring.
Nutrient solution heaters have a temperature setting (set to 21oC), the heater will come on to ensure temperatures don’t drop below this figure. These heaters are submersible and have suckers to attach to the bottom of your tank or reservoir. It is important to ensure that your nutrient heaters are always fully submerged when turned on – they are likely to crack or break if turned on whilst not in liquid.
To help keep the nutrient solution going above this temperature when the light is on, try and maintain good grow room temperatures with a sensible air exchange system. Don’t let any light hit the solution. You may also want to provide extra protection from the light and heat on your reservoir by using reflective sheeting or blowing an oscillating fan to cool the sides of the reservoir. On NFT Gro-Tanks use an layer of black/white sheeting on top of the plastic correx cover for extra shielding, especially when plants are young and there is no canopy of leaves to protect the tank from getting too warm in summer or warmer conditions.
Aeration
As a system, NFT is good for providing the high levels of oxygen needed in and around the root zone. Good oxygenation is essential for nutrient mineral uptake by the roots and to aid other metabolic functions when in the plant. The more light and heat that your plants are exposed to, the more water and oxygen is needed. This is why plants will often be a lot healthier and do a lot better in an active hydroponic system (such as NFT) than in pot based systems when under high light conditions. Your system is only as good as the weakest link, and the constant recirculation in an NFT system will keep a good level of oxygenation in the nutrient solution.
Airstones are often a good idea even in a well oxygenated system like NFT, especially when combating warm conditions to ensure the water has as much oxygen as possible. Airstones in your reservoir will also help to keep the solution stimulated and moving as well as helping to buffer the pH a little. It is also possible to boost the air content of your nutrient solution chemically by using Oxyplus but it is imperative that you don’t use this product with organic or biological boosters and additives.
Solution Changes
As a general rule you should always change your solution for a fresh batch once every 1 - 2 weeks, the theory being that the more often you do it the better the final results. With large nutrient reservoirs this rule of thumb works well, but with smaller reservoirs new solutions may be required every 3 to 5 days. A separate container is often useful for making up new solutions, which can then be poured or pumped into your empty reservoir.
When topping up reservoirs between batches of fresh solution, top up with a quarter strength hydroponic nutrient solution. Use this weak top up whatever stage of growth you are at. This weaker strength top up solution will work well on both small plants which are using weaker feeds, and with bigger plants on stronger solutions where the plants tend to drink more water. This weaker top up will prevent nutrient solutions from getting too strong between solution changes. (Note: if plants are quite dark green, then use just water when topping up reservoirs and/or use slightly weaker strength feed generally.)
pH adjustment
When making a fresh batch of nutrient solution, always add the feed to the water first and then adjust the pH of the solution to between 5.5 and 6.5 - ideally about 6. This will save you adjusting the pH twice as the feed may also affect the pH.
Your pH will change on a daily basis, usually going up every day. This is quite normal. It’s best not to adjust the pH daily as this can result in too much phosphoric acid in the nutrient and can lead to nutrient problems, it is much better to let the pH drift for two or three days after initial setting before re-adjusting.
If your tap water pH and cF is high you may need a hard water feed which will help reduce the pH and reduce the amount of pH Down needed. Nitric Acid is also available as an alternative pH Down in the leaf growth phase.
Irrigation
Assuming that you are using 7.5cm (3”) or 10cm (4”) Grodan Transplanting Cubes or small baskets of cellmax in high light conditions, we can split the irrigation into two basic stages:
Stage 1 – manual watering or pump on timer
Before the roots have emerged from the transplanting cube, either turn the pump on manually once a day just to re-wet the cube or put the pump on a timer to come on once a day for a few minutes, this will keep the bottom of the cube drier and encourage the roots to come out of the cube in search of water and food.
Stage 2 – pump on 24 hours
Once the roots are nicely out ofthe bottom of the transplanting cube it is best to run the nutrient solution all the time, night and day.
Assuming you are growing in a high light situation with healthy plants drinking every day, and that the solution is at the optimum temperature and is well oxygenated, running the solution all the time will give you the best results.
If you want to experiment with irrigation cycles then make sure that you never have the nutrient off for more than 15 minutes at a time day or night, as this will chill the roots through the cooling effect of evaporation of water. This leads to cellular damage to the surface of the root zone which will show up as a slight browning of the roots.
Boosters
All your plant needs to get a good result is a hydroponic grow and bloom nutrient package, although there are many good additives and boosters that improve nutrient uptake, contain natural enzymes and hormones, vitamins and beneficial bacteria. Check out the Growth Promoters & Nutrient Additives category on the left for our full range of boosters.
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