In addition to light and carbon dioxide all plants, whether they are grown in soil or in indoor grow rooms, need a steady supply of fresh air. While this is achieved naturally in outdoor gardens, fields, farms etc., in hydroponics gardening special means have to adopted to ensure air movement for continual supply of fresh air. This is done using fans blowers and associated equipment. As air that becomes stale can no longer support plant growth it has to be vented while fresh air has to be introduced to take its place. Providing a well designed system for the movement of air inside the grow room therefore assumes paramount importance in hydroponics.



Air movement helps maintain ideal levels of several parameters such as temperature, humidity and carbon dioxide in the grow room. These parameters need to be effectively controlled in order to avoid a number of problems. Though complete control over these parameters is not required, some control has to be provided for to ensure that vital plant processes like transpiration are not adversely affected. Transpiration is the process by which water in the plant is evaporated to the surrounding air. Transpiration can happen only when the surrounding the air temperature is within a certain range neither high nor too low. Efficient air movement which ensures heat dissipation and temperature control facilitates transpiration.

Temperature & Carbon dioxide Availability

Though efficient movement of air has a positive effect on a number of processes, its greatest effect is seen on carbon dioxide availability. For photosynthesis to take place, carbon dioxide and light must be available to plants in adequate quantities. Carbon dioxide is naturally present in the atmosphere to the extent of 300 ppm while the light is provided by the lighting system installed in the grow room. Plants in the grow room will, over a period of time, consume the available carbon dioxide necessitating fresh supplies of the gas. In the absence of air movement the process would stop. The venting of carbon dioxide depleted air and addition of fresh, cool carbon dioxide rich air ensures that this does not happen and carbon dioxide is always available for uptake by the plants.

The uptake of carbon dioxide from the surrounding air happens through stomata - microscopic openings on the underside of the leaves. Carbon dioxide absorbed by the stomata is used to make Adenosine Triphosphate (ATP), the major source of usable chemical energy in metabolism. Humidity and temperature ranges trigger the opening and closing of these openings to regulate internal processes. Air temperatures within 65-80 deg. F are ideal for indoor grow rooms. The upper limit can be raised to 85 deg. F with carbon dioxide supplementation. It has been shown that higher temperatures up to 90 deg. F increase the rate of photosynthesis. Beyond 90 deg F, the stomata close to cut excessive transpiration. This starves the plants of carbon dioxide with disastrous effect on yields.

Humidity Considerations

Humidity in the grow room is also an important factor that needs to be controlled as it influences several plant processes. Water is taken up by the plants for normal metabolic processes and excess water is released to the air as water vapor through transpiration. A few gallons of water is thus released by plants in a grow room adding to the humidity. This process is accelerated at higher air temperatures as plants attempt to cool themselves by releasing greater amounts of water vapor. Hence higher temperatures will lead to higher humidity in the grow room.

Relative humidity ranges of 40-60 % are ideal for most plants as optimum carbon dioxide absorption occurs within this range. Higher relative humidity levels affect the carbon dioxide absorption rate as the stomata’s absorption capacity is reduced.

High humidity may also lead to heavy condensation problems. This may happen when temperature drops 10 -15 deg. F, following the switching off of grow lights. In humid conditions this can lead to heavy condensation as the air’s capacity to hold water vapor gets reduced. Water droplets get deposited on grow room surfaces in which colonies of fungi and mold are formed. These may then reproduce releasing spores that can spread throughout the foliage causing extensive damage if left unchecked. The best way to avoid this problem is to ensure that all hot air is vented out of the room so that no condensation can occur.

It can be appreciated from the above that humidity in the grow room cannot be allowed to build up and needs to be controlled. Humidity control in the grow room can be achieved by ensuring movement of air. This can be done in a number ways with varying degrees of efficiency. Perhaps the simplest approach is to install a humidistat and a fan. The humidistat allows for the setting of upper limits on humidity. This does not allow high humidity levels to build up and prevents excessive condensation. Removing this air and moving fresh air in the grow room helps maintain the right conditions for plant growth.

Oscillating Fans

Since the foliage of the plants is where various processes like transpiration, absorption of carbon dioxide etc. take place, oscillation of air around it can create better conditions of temperature and humidity. It has been observed that using an oscillating fan helps mixing of the warm and cool air, reduces humidity around the plants and keeps the stomata open. An additional benefit is the high carbon di oxide content of the new air. Oscillating air also helps in pest control. A number of garden pests become uncomfortable under the high breeze of an oscillating fan and find it difficult to breed in such hostile conditions.