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Why Do Greenhouses Need Ventilation?

Category: Gardening Tips and Guides | Posted: Wed May 18, 2022 4:41 pm

Whether a hobby grower or a commercial gardener, greenhouses are valuable tools to help extend your growing season and maximize yields. While it's commonly known that sunlight, water, and healthy soil are essential to plant growth and health, there is another key consideration when designing a greenhouse: ventilation.

As we will discuss, ventilation is essential for maintaining healthy plants and reducing the risk of disease in your greenhouse.

Why Greenhouse Ventilation Is So Important

1. Essential for Growing in a Greenhouse
Proper ventilation is essential for growth in a greenhouse. While the primary purpose of ventilation is to provide fresh air, it's also important for reducing the temperature, preventing disease, removing pollutants and providing pollination.

While many growers choose to use fans to ventilate their greenhouse, passive ventilation techniques can be just as effective with the right structure design. Properly designed structures will allow you to provide sufficient airflow without investing in expensive fans or other equipment that must be purchased and maintained on an ongoing basis.

2. Reduces Heat Buildup
Think of it this way: if you are wearing a jacket on a hot day and you feel like you're sweating, you'll probably want to take the jacket off. That's because the excess heat is not able to escape through ventilation. The same is true for your greenhouse—plants need air circulation to help keep them from overheating.

If your greenhouse is overheating, there’s a good chance that it doesn’t have enough ventilation.

Your plants are wilting or dying from heat stress
Temperatures inside the greenhouse are above 80 °F (27 °C) when outside temperatures are below 70 °F (21 °C)
You see signs of heat stress on the greenhouse itself, like condensation and fogging on the panels or doors that won’t close easily because they swelled shut
wilting plants

There are many ways to prevent heat buildup in greenhouses. One of the most effective is installing ventilation fans. Properly sized and placed fans can reduce temperatures significantly.

3. Humidity Buildup and Damping Off
Why is humidity an issue for plants?

Simply put, higher humidity levels can cause disease in plants. When humid, diseases that are spread by water vapor are able to survive and thrive in the greenhouse. The high humidity encourages pathogens to grow and replicate, which is why you often see these diseases during humid weather.

Yes, plants produce bacteria-fighting compounds when faced with high humidity levels. However, this increases the energy requirements of the plant, affecting its growth rate and the development of flowers and fruit. That's wasted energy...

Since you can't control the weather conditions outside, it is necessary to control them inside the greenhouse. This is especially critical during the winter when heating your greenhouse can cause problems due to inadequate ventilation and high humidity.

Damping-off, or the sudden wilting and dying of sprouting seedlings, is a common symptom of a fungus that thrives in high humidity. If you've ever felt completely frustrated by how many times you had to start your seedlings over because they kept mysteriously rotting at the roots, ventilation could be the answer.

Ventilation will help keep these problems at bay to ensure a strong, healthy crop of fruits and vegetables.

4. Airflow
You might already know that plants need sunlight, water and soil to survive. But did you know that they also need fresh air? This is because plants rely on carbon dioxide for food, just like we rely on oxygen. If your greenhouse does not have enough ventilation, the stale air inside it will become depleted of carbon dioxide. Your plants will begin to die from a lack of nutrition.

Plants need both CO2 and O2 to grow. Plants release oxygen during photosynthesis, but they also need it to breathe. When there isn't enough oxygen in a plant's system, it ultimately starves to death.

This is why greenhouses have vents: CO2 is heavier than oxygen so it tends to sink towards the ground where plants are growing—but if you don't let some fresh air in every now and then, those plants are going to run out of CO2 fast!

5. Lack of pollination and Poor yields
First of all, pollination is necessary for the healthy development of your plants and for good yields. It’s important that pollinators have access to your greenhouse, but if your greenhouse isn’t ventilated properly, they won’t be attracted to it.


If the greenhouse is too humid and there is not adequate ventilation, pollen won't be released. Or if it is released, it will fall before reaching its target plant. Lack of pollination can result in reduced yields and poor fruit quality.

Stale air can also make plants more prone to diseases and pests. For example, the greenfly is an aphid that likes warm damp conditions. Aphids excrete sticky honeydew which can encourage the growth of a sooty mold on plant leaves and flowers, reducing their quality and marketability. If you keep your greenhouse well-ventilated it will reduce the risk of these insects finding a home in it!

Final Conclusion
Ventilation is an important part of the greenhouse building process. Even in natural-air greenhouses, ventilation plays a vital role. While some greenhouses are self-ventilating, other greenhouses use additional equipment to provide improved air circulation and heat management. Greenhouses need good ventilation to control humidity and temperature levels, prevent disease spread and overheating, reduce heating costs and save energy, etc.

As long as you keep the greenhouse environment properly ventilated, the temperature and humidity will stay at levels that are optimal for plant growth. The recycling of the air in a greenhouse is critical to sustaining plant life, which is why maintaining proper air circulation is such a big deal.


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