Photo of a circulation fans in a commercial polytunnel in Korea

One of the most important factors to consider when growing produce in polytunnels is ventilation, and there are certainly plenty of benefits to ensuring that there is adequate air movement inside your polytunnel. Airflow not only helps to reduce condensation but also limits the risk of fungal disease and encourages the evaporation of moisture through leaves - thereby increasing nutrient uptake.

In his 1955 study in the Annals of Botany, R M Wadsworth observed that the growth rate of plants rises with wind speed at low wind speeds, but that this positive relationship falters when wind speeds are increased further. Many growers also use air movement to help build stronger and more physically resilient plants, as the movement of plant stems and branches stimulates the production of ethylene, a hormone which manages various growth aspects. 

On the other hand, it has also been shown that whilst air flow increases height and stem conductivity, stem flexure can result in reduced height and stem conductivity, suggesting a ‘clear trade-off between the mechanical and hydraulic functions of the stem’. Maintaining a fine balance between airflow and stem flexure for the plants in your polytunnel is therefore of great importance should you wish to achieve optimal growing conditions. 

Another aspect of polytunnel ventilation is air circulation, which helps to regulate the temperature inside your polytunnel. It is common knowledge that plants will generally grow faster as the heat in your polytunnel increases, but high temperatures can slow down germination and negatively impact on photosynthesis, respiration and membrane stability. It is therefore also important to control temperatures inside your polytunnel to the best of your ability.

Thankfully, there are a number of solutions and products which can provide growers with the control they need. In smaller structures, adequate ventilation can be achieved by simply opening the doors. Opening both ends of a polytunnel allows air to pass right through, lowering the relative humidity inside the tunnel and allowing plants to cool down. For larger polytunnel structures, however, more intensive methods of ventilation are often needed. 

One method of providing your crops with continuous yet optimal air movement is with the use of a circulation fan, which can move large volumes of air and help to preserve a constant, level environment in your polytunnel. Having been designed to extract excessive heat and stale or humid air, polytunnel and glasshouse circulation fans are ideal for use with larger polytunnels where heat can often build up in the middle and where doors are unable to be opened.

For larger growers, sophisticated automatic ventilation systems can help to improve the efficiency of labour by making decisions based on the temperature inside your polytunnel and responding accordingly. Thermostatic operations allow growers to control temperatures precisely, whilst providing you and your employees with more time to focus on other priorities. These advancements help to close the technological gap between modern glasshouses and polytunnels. 

As we have seen, creating an even temperature and harmonised environment in your polytunnel through the use of appropriate methods of ventilation results in optimal growing conditions for your crops and plants. Consequently, this can have a beneficial effect on your business by maximising crop revenue and improving your business’ sustainability.