Do Greenhouses Need Ventilation

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If you’ve recently built a greenhouse, or maybe you are thinking about building a greenhouse, and you are wondering if they need ventilation. And as it turns out, ventilation plays an important role in the success of a greenhouse.

Do Greenhouses Need Ventilation? Greenhouses absolutely need ventilation. It is critical to regulating the temperature and humidity of the greenhouse as well as providing carbon dioxide for your plants. Without ventilation, your greenhouse plants may not survive.

Now that it has been established how critical ventilation is for plant growth, read on to find out more about how you can provide the proper ventilation for your greenhouse.

Why Ventilation a Greenhouse

You may be wondering why ventilation is so important for your plants’ success and this is actually for a variety of distractions

Controls Temperature

Everyone knows that plants need heat in the colder months. But did you realize too much heat can actually cause damage to your plants? Having ventilation allows excess heat to escape your greenhouse which in turn keeps your plants from damage caused by excessive heat.


Just as the temperature in a greenhouse is critical, so is the humidity levels. Although you need some humidity for the plants to be able to survive, too much can build up and cause problems such as mold and mildew. When you have proper ventilation in your greenhouse, this solves any humidity build-up issues.

Carbon Dioxide

Plants need carbon dioxide to flourish and complete their photosynthesis process. If you aren’t providing artificial carbon dioxide for your plants, the only way they can get this is through proper ventilation. If you don’t have proper ventilation, this is the equivalent of depriving someone of air, your plants won’t grow because they will not be able to breathe.


In a greenhouse, pests can be a common worry as they can easily cause problems such as eating your plans and becoming a nuisance. Common greenhouse pests include aphids, gnats, shore flies, bloodworms, mites, slugs, and snails. If your greenhouse is too humid and warm, this creates a breeding ground for all of these creatures and your pest problem will multiply. When the temperature and humidity in a greenhouse are kept down with ventilation, this will help you control the pests as well.


Unless your greenhouse has a beehive (Which is unlikely) you need to find a way to artificially simulate pollination so your plants can grow. And this can easily be done with a proper ventilation system which includes fans to blow pollen from one plant to the next. If you think you may have a pollination problem in your greenhouse but you aren’t sure, check how well your plants are bearing fruits. If there are no fruits, you have a pollination problem and ventilation may be the culprit.

Types Of Ventilation

You’ve realized by now that you desperately need a ventilation system for your greenhouse, but maybe you aren’t sure where to start. In greenhouses, there are generally two types of ventilation systems, and those are natural and mechanical ventilation.

Natural Ventilation

Natural ventilation usually lives up to its name in that you use all-natural methods in order to ventilate your greenhouse—meaning you don’t use any electricity. This method relies on the wind and thermal buoyancy, which is usually established via strategically placed vents or open windows. The vents are normally placed on the roof since hot air typically rises, and then this creates a vacuum that draws in air from the windows or vents on the sides of the greenhouse.


Although Natural ventilation is generally cheaper, as it doesn’t use any fancy devices or electricity, it can be much harder to control. So if you are cultivating plants with very specific temperature and humidity requirements, this may not be the method for you. Natural ventilation also tends to allow some pests in the greenhouse which could bother your plants. You are also relying on the outside weather. Therefore, if you are thinking of choosing natural ventilation, make sure you take the weather in your area into account.

Mechanical Ventilation

Unlike natural ventilation, mechanical ventilation relies on machinery and electricity to function. These systems usually employ a series of fans, or other mechanical devices to circulate air through the greenhouse. These systems can be automated based on a timer, temperature, or can be controlled by switches that a gardener must turn off and on.

Mechanical ventilation systems can often be very convenient, as the gardener has a lot of control over the temperature and humidity level in the greenhouse. But of course, this costs money and does take some time to regulate. There are lots of tradeoffs though. When you use mechanical ventilation there are no pests, nor do you have to rely on the weather like natural ventilation. And if you live in an area with unpleasurable weather, it’s probably best not to leave your greenhouse ventilation up to chance.

How Do I Pick?

If you are having trouble deciding which ventilation system is best for you, even after considering the weather in your area, and the plants which you wish to grow, there are a few other deciding factors you can consider.

The Construction Of Your Greenhouse

If your greenhouse is made of rigid materials, it may be difficult to generate enough airflow to support a natural ventilation system. If this is the case for your greenhouse, you probably want to consider a mechanical ventilation system as then you can easily control the air which flows in and out of your greenhouse.

The Size of Your Greenhouse

With natural ventilation systems, it’s important to make sure that the air which does flow through your greenhouse reaches all of your plants. And if you have an especially large greenhouse, you will need enough vents to make this happen. Mechanical ventilation systems are much easier to control to ensure that all plants receive sufficient air.

A Third Solution

If you are looking at this and you would like to use natural ventilation but you also aren’t sure if it will work for your greenhouse, there is a third solution. You can have a natural ventilation system with an electronic component such as a ceiling fan, to help with air circulation. Although this combination system is not fully natural, it can help with a natural ventilation system without having to fully go the mechanical route.

Setting Up

Whichever route you have chosen for your ventilation needs, there are several things you need to do to get your system up and running.

Natural Method

With natural ventilation, the set-up process entails making sure that you have enough vents to sufficiently serve the size of your greenhouse. The number of vents you need is generally measured in feet per the size of your greenhouse. Generally, you need 20% of your square footage of the entire greenhouse as the square footage for your vents on both the roof and sides. So if the square footage of your greenhouse is 300 sq. ft. you will need 60 sq. ft. of vents on the ceiling, as well as 60 sq. ft. of vents on the sides. This is also where you would consider installing a ceiling fan.

Mechanical Ventilation

When setting up a mechanical ventilation system you need to consider which months you will use your greenhouse. This is because you need to base your fan size on the hottest month in which the greenhouse will be used. You want to buy a fan that will change the volume of air in your greenhouse at the rate of one time per minute. To calculate the cubic volume of your greenhouse, then buy a fan with that cubic rating.

If you intend to use your greenhouse in the colder months as well, you probably want to consider attaching your fans to a thermostat so they will turn off when they are no longer needed. Or, you can have someone constantly monitor and turn off the fans when the temperature drops below a certain temperature. Even if you are using a mechanical ventilation system, it may be helpful to install rooftop vents or a ceiling fan to assist with the ventilation process.


The last topic to discuss is heating. When it comes to ventilation, if you live in a colder climate, you may need to add auxiliary heating to your greenhouse in the winter. Usually, this only applies if it falls below 50 degrees in your greenhouse. Even if it doesn’t fall that low, you may still need to use auxiliary heating if you are using natural ventilation, as more cold air is likely to enter the greenhouse through the vents.


Proper ventilation is one of the most critical parts of operating a greenhouse. Without proper ventilation, your plants may get too hot, overrun by pests, or may not get enough carbon dioxide. The type of ventilation system you need to install varies widely on the climate of where you live, as well as the type of greenhouse you own. But no matter which system you pick, having a ventilation system is one of the best things you can do for your greenhouse plants.

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