How to ventilate a greenhouse – 3 ways to keep your plants cool in summer

Providing air circulation for plants is the key to successful greenhouse gardening

Greenhouse ventilation
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As outside temperatures warm up and we enjoy sunnier days, you might be starting to grow more in your greenhouse. If you notice that your greenhouse plants aren't doing well despite lots of light and plenty of water, it could be an indication that you aren't providing enough ventilation. 

When you're considering greenhouse ideas for your backyard, ensure you take into consideration how to keep it ventilated, especially during hotter months. Even if you're making your own DIY greenhouse, you should consider including ways to provide airflow to ensure your plants grow healthily. 

Not sure where to start? Don't worry, we've enlisted expert advice about the importance of airflow for plants and how to keep a greenhouse ventilated.

Rustic greenhouse with hardy and tender perennials

(Image credit: Allan Pollok-Morris / Future)

Why do greenhouses need ventilation?

When planning a greenhouse, you need to make sure you're remembering ventilation. This is because your greenhouse plants need air circulation to both stay cool and to establish healthily.

'Air circulation is important because this prepares seedlings for the outside environment, provides carbon dioxide to plants which is essential for photosynthesis, limits pathogens and diseases from spreading and limits humidity,' says Sarah Warner, organic growing expert and farm associate at Case Western Reserve University Farm.

'Keeping a greenhouse as cool as possible is important because high temperatures can stress plants and also cause you to water more,' she adds.

One of Monty Don's greenhouse tips is to keep it cool so that it doesn't become a hot house. Failing to do so could have detrimental impacts on your plants.

'Without ventilation, there's a danger of diseases, especially fungal diseases, taking hold and killing the plants. Plants breathe through their leaves and do need a constant flow of air for this,' says Annette Hird, expert gardener at Easy Urban Gardens.

Sarah Warner
Sarah Warner

Sarah Warner is a farm associate with the farm food program at the University farm. She has five years of experience growing organic food in Northeast Ohio. She is a Lorain County Community College graduate with an Associates Degree in Sustainable Agriculture and is also certified in Permaculture Design.

Annette Hird
Annette Hird

Annette Hird has an Associate Diploma in Horticulture and is an urban gardening expert. She has worked as a professional propagator and managed, maintained and improved many urban and rural gardens. She also enjoys growing her own fruit, vegetables, herbs and flowers as well as many different types of ornamental plants.

How to ventilate a greenhouse

Shelves in a greenhouse with terracotta and metal pots, plants and watering can.

(Image credit: Future)

Whether you're growing herbs in a greenhouse or the best food to grow in a greenhouse, it's important to keep your greenhouse ventilated if you want successful growth. We've asked experts about the different ways you can go about this. 

1. Open the vents

Greenhouse open vents

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It may sound obvious but you can increase airflow in a greenhouse by opening the vents. These are windows, often on the side or roof panels that can be opened to provide ventilation.

'Side vents that allow wind to blow horizontally through are great to have but not totally necessary,' says Sarah. 'Roof vents are absolutely vital and I believe to be the most important,' she adds.

You might also find that your greenhouse has a ridge vent on its roof. 'Ridge vents work like a chimney exhausting hot air through the peak of the roof,' notes Pam Morin, greenhouse manager at Johnny's Selected Seeds.

Even if you are trying to heat a greenhouse, opening vents can prove beneficial for your plants. In hotter months, it can be a good idea to keep vents open for the majority of the day to regulate temperatures and provide air circulation. 

Pam Morin
Pam Morin

Pam Morin has been the Greenhouse Manager at National Garden Bureau member Johnny’s Selected Seeds since 2012, where she is responsible for the day-to-day care of research and breeding crops. She oversees 40,000 square feet of heated greenhouses for seedling production, unheated hoophouse trials grown in the ground, and several pollination projects for seed production.

2. Open the door

Greenhouse ventilation

(Image credit: Johner Images via Getty Images)

Not only can you open your greenhouse vents to provide air circulation, it can be wise to simultaneously have your greenhouse door open to allow air to flow between the two.

'Even better, if there's a door at either end you can open both for airflow,' says Annette.

'Windows and doors should be opened daily if it's hot outside and left open during the hottest part of the day,' she adds.

Experts note that it can be beneficial to open your greenhouse door first thing in the morning. 'Letting cool morning air in will keep temperatures down until the afternoon. Early morning is when my roof vents and doors open and I close the doors around 5:00pm, after the hottest point of the day passes,' says Sarah.

3. Use a fan

Greenhouse ventilation

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Another way to ventilate a greenhouse and increase air circulation is by installing a fan. This can be suspended from the roof or placed on the floor or a windowsill

'I encourage using a fan in the greenhouse because afternoon temperatures can be so hot that you will need a fan for an extra boost of ventilation to keep the plants cool and air flowing through,' says Sarah.

There are different types of fans you can get for your greenhouse, although experts recommend getting greenhouses with a built-in exhaust fan.

'Exhaust fans work with the shutters on the opposite end of the greenhouse and the fan will pull cooler outside air through the greenhouse horizontally,' says Pam.

'If you don't have an exhaust fan built into the end of the greenhouse you can put a regular house fan in a window to help pull out the hot air,' she adds.

If you are considering installing a fan to keep your greenhouse cool, something to be aware of is how much it costs to run a fan 24/7.

Find a fan for your greenhouse online


Should I ventilate my greenhouse in winter?

No matter the time of year, greenhouses need ventilation. In winter, greenhouse ventilation is most important for reducing humidity and condensation. This is caused by the warmer temperature inside the greenhouse compared to outside. You may choose to opt for a fan during winter which will allow you to provide constant air circulation. You can also open vents and doors, but be aware that your plants shouldn't be overexposed to the frosty temperatures outside.

Should I leave my greenhouse door open at night?

During the summer, you may choose to leave your greenhouse door open at night to provide air circulation. This is especially beneficial if night temperatures remain high. However, be cautious to leave your greenhouse door open at night during winter where temperatures may drop too low because the cold air could damage your plants.

If you want successful greenhouse growing, it's key to provide plenty of ventilation. Open vents and doors and use fans to provide air circulation, encourage healthy plant growth and keep diseases away.

You might want to also read up on how to use a greenhouse in winter and how to winterize a greenhouse to ensure you take the right steps with your greenhouse during colder months.

Tenielle Jordison
News Writer (Gardens)

Tenielle is a News Writer in the Gardens team at Homes & Gardens with five years of journalistic experience. She studied BA Journalism, Media and English Literature and MA Magazine Journalism at Cardiff University. Before coming to Homes & Gardens, Tenielle was in the editorial department at the Royal Horticultural Society and worked on The Garden magazine. She is passionate about sustainable living and likes to encourage gardeners to make greener choices to help tackle the effects of climate change with a trowel in hand. Tenielle is also a houseplant lover who is slowly running out of room for her ever-growing collection.