Greenhouses are an incredible tool for plant cultivation. Whether your interest is in a small hobby greenhouse for your backyard, or operating a large commercial greenhouse, these structures enable growers to command their growing environments and successfully cultivate crops in much wider geographic and seasonal ranges than is possible in open air cultivation. While the benefits of greenhouses are many, a poorly equipped greenhouse can do more harm than good for the health of your plants. The most fundamental requirement for any successful greenhouse is ventilation. Without adequate ventilation, greenhouses will stifle and suffocate plants impairing growth and increasing the chances of plant disease or even death.
In this post we will review the basics of greenhouse ventilation, types of ventilation and simple system design tips for greenhouses both large and small.Â
Why Ventilate a Greenhouse?
All greenhouses require some form of ventilation. Without fresh air passing through a greenhouse, temperatures can become too high, and plants will suffocate due to insufficient gas exchange. During the day, as plants photosynthesize, carbon dioxide (CO2) is absorbed by the plant and oxygen (O2) is released through tiny holes on the plant’s foliage called stomata. When temperatures are too high, or the concentration of CO2 in the greenhouse is too low, photosynthesis stalls, growth falters and plants may become severely stressed.Â
Unventilated greenhouses are also susceptible to becoming too humid. Plants carryout a process called transpiration which involves water moving up through the plant’s tissues from the roots. Some of that water is eventually released through the plant’s stomata into the surrounding air as water vapor. Unless the air in the greenhouse is exchanged, this water vapor will continue to increase humidity to detrimental levels. Harmful plant molds and mildews thrive in elevated humidity, and such an atmosphere can expose your crop to severe risks.Â
The plant stomata which we mentioned above are also sensitive to air movement. Gentle air movement will help stomata to remain open, allowing plants to efficiently photosynthesize. Air movement that is insufficient or too fast will cause stomata to remain closed, hampering the plants processes. Air movement through the plant canopy will help to maximize plant photosynthesis, by helping plant stomata to remain open. This air movement through the plant foliage also helps to eliminate pockets of stale air that may be warmer and moister than the surrounding atmosphere.Â
In an unventilated greenhouse all these factors can significantly reduce fruiting and flower yields and even kill plants.
Types of Greenhouse Ventilation
To provide for fresh air through a greenhouse, at a minimum, most greenhouses will be designed with some roof vents. When vents are opened the convective effect of hot air rising will allow some air to move out through the vents and hopefully pull some fresh air in through a door or alternative vent. This concept is called passive ventilation. During the cooler months in temperate climates passive ventilation may be enough to maintain an acceptable temperature. However, passive ventilation is quickly overwhelmed during warmer weather and plants will likely struggle without an appropriate exhaust fan. Snap-Fan exhaust fans will pull the warm, humid and O2 rich air out of the greenhouse, while simultaneously drawing in cooler CO2 rich air from outside.
Greenhouses should also employ circulation fans. Air inside greenhouses will stratify, that means to separate into layers of differing temperatures and humidity. Circulation fans are placed in the greenhouse to mix the air mass inside to ensure that the entire greenhouse acts as one atmosphere with similar temperature and humidity throughout the space. This is good for the plants and helps the exhaust fan and other HVAC appliances to operate most effectively. Snap-Fan circulation fans provide gentle air movement through the plant foliage. This brings fresh CO2 to the plant’s stomata, helps the plant to photosynthesize and flushes out any dangerous pockets of heat and humidity that may be trapped within the plant canopy.Â
Ventilation Solutions for Greenhouses Large and Small
Whether your greenhouse is very large or small, the same principles apply to your structure. Air inside should be exchanged for fresh air from outside using an exhaust fan that is sized for your specific case. And the air inside your greenhouse should be circulated around using fans to maintain a uniform environment inside, as well as maintain a constant gentle air movement across the surfaces of your plants. Snap-Fan offers a wide range of fans for all types and sizes of greenhouses. We are always happy to help recommend our best options for your specific greenhouse.
Choosing the Right Ventilation System for Your Greenhouse
All greenhouse ventilation systems should be sized to the greenhouse that they will operate in. The location of the greenhouse and typical outside air temperatures during your growing season should also be considered.Â
Greenhouse exhaust fans should be sized to the greenhouse so that the exhaust volume is able to change all the air inside the greenhouse once every minute. To estimate this, we calculate the total volume of the greenhouse and compare this to the cubic volume of air that each fan can move in one minute. In the United States this is typically referred to in cubic feet per minute (CFM).Â
Circulation fans should be selected to provide consistent air flow coverage throughout the square footage of the greenhouse. Circulation fans will typically be hung above the plants and should typically be close enough for airflow to penetrate the plant canopy, without being too close so as to harm plant foliage. For hardier plants or denser plant canopies fan size and wind speed may be increased.
Recap
Every greenhouse can benefit from appropriate ventilation. Plants may just be surviving in a greenhouse without fans. Stories abound about how the addition of just a fan or two can have a tremendous impact on the vitality of a greenhouse crop.
FogCo offers the Snap-Fan line of exhaust and circulation fans, designed with greenhouses in mind. Snap-Fan’s high quality and efficient fans can be sized for any greenhouse project. Visit our Snap-Fan page to learn more about our Snap-Fan ventilation products and how they can be utilized to improve the growing environment in your greenhouse space.
