Plants transform carbon dioxide into sugars as part of the photosynthesis process, so sitting in a greenhouse filled with old, stagnant air won't do them any good. Greenhouse ventilation helps to optimize the environment of your structure throughout the year, extending your growing season and producing the highest yield at the best quality. A good greenhouse ventilation system will:
There are two main types of greenhouse ventilation: passive and active. In order to create the best possible environment for your plants, we recommend that you use both.
Passive ventilation is the natural airflow that enters and exits your greenhouse via any open areas in your structure. You can use roof vents, wall vents or roll-up walls to let fresh air enter your greenhouse, but it's preferable to use a combination of wall vents and roof vents, or all three. The wall vents and roll-up walls will let in cool, fresh air, while the roof vents will let the hot air escape as it rises.
Active ventilation refers to the artificial airflow provided by fans and evaporative coolers within the greenhouse. Greenhouse fans are especially necessary because, even with roll-up walls, there will likely be many days during the growing season that aren't breezy enough to circulate air in your structure. An evaporative cooling wall is also important for warmer climates because they pull in excessive heat and redistribute it as cool, moist air that plants love.
The combination of passive and active greenhouse ventilation will allow you to extend your growing season and maintain a consistent, healthy environment for your plants, at least in terms of air quality. That being said, it can be costly to add a greenhouse ventilation system to your structure — greenhouse fans and evaporators require electricity and the coolers consume water, which may offset any savings accrued from watering your plants less.
Take the time to think about the size of your operation, the types of plants you're growing and the climate you live in before investing in a state-of-the-art greenhouse ventilation system. If your climate is cool enough, you may only need fans to keep the air in your greenhouse moving. If you're further south, you may need to add the evaporative cooling wall to your list as well. The best thing you can do is stick to what you know you will need to maximize yield and produce your best crop yet.