Transpiration is a process used by plants to maintain their temperature when the environment is too warm. It serves the same functions as sweating in some animals. In order to cool the area around it, plants release water through the leaves.

High rates of transpiration will occur if the temperature of the growing environment is too high, and this can seriously effect the nutrient solution. As a plant transpires, it will draw up more water from the solution to replace that which has been lost. This will have an impact on the nutrient:water ratio of the solution, which will effect both pH and conductivity levels.

High rates of transpiration can cause particular problems in systems with small reservoirs, so these will probably need topping up on a daily basis.
It can also cause problems in hard water areas, as adding lots of water can lead to a build up of salts etc. In this situation the nutrient solution should be removed from the reservoir and replaced with a fresh solution at least every 4 — 7 days.

If the temperature does get too high, and the plant starts using a lot more nutrient solution than normal, then the following action should be taken.

• Check and correct the nutrient solution on more regular basis, every day if possible.

• Maintain pH and conductivity levels slightly lower than normal in order to compensate for the sharper rise caused by high transpiration rates. Refer to section: extreme rises in pH and conductivity.

• Keep the reservoir topped up, at least above 50% capacity at all times. If it goes below 20% it will be more like a soup than a nutrient solution.