To ensure your greenhouse provides a healthy environment for your plants to grow in it is vital that you get the ventilation right. In our guide we will show why ventilation is important and what we can do to improve existing ventilation in a greenhouse.
Why Is Greenhouse Ventilation Important?
Good ventilation in a greenhouse will help to prevent lots of problems, equally poor ventilation in a greenhouse is likely to cause problems for your plants. If you have poor ventilation, you could expect to see the following problems:
- Poor Plant Respiration - Respiration is when plants ‘breathe’, with the leaves of the plants taking in oxygen and releasing carbon dioxide.
- Reduced Photosynthesis - Photosynthesis happens during the day, with the plants absorbing carbon dioxide and producing oxygen.
The best way to ensure good respiration and photosynthesis is to ensure good ventilation enabling fresh air to be provided to your plants. Even though the levels of respiration and photosynthesis change throughout the year due to different temperatures and weather conditions, ensuring healthy growth all year round means making sure there is adequate ventilation in your greenhouse throughout the summer and the winter.
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Fungal Infections
All greenhouse gardeners should be aware of the possibility of fungal infections as a greenhouse provides the perfect environment for fungal infections to grow quickly. Spreading via spores in the air, they will increase and spread rapidly in warm, wet environments, exactly what you are likely to find in your greenhouse through the summer months.
To help reduce fungal infections and their spread amongst your plants, allow fresh air to enter and circulate throughout your greenhouse and the easiest and most efficient way to do this is to ensure good ventilation.
Types Of Greenhouse Ventilation
Greenhouse ventilation is all about utilising ventilation and getting air from outside of your greenhouse inside and creating a flow of this air through your greenhouse so that your plants are exposed to fresh air no matter where they are positioned in your greenhouse.
Getting fresh air into your greenhouse means there needs to be areas within your greenhouse where air can easily enter – the door, the windows in the roof and the vents in the side of the greenhouse.
Ideally you want cooler air to enter through the louvre vents (more on these later) - which are usually fitted low to the ground on your greenhouse – with the air rising to the roof of the greenhouse and escaping through the vents there. This way you are creating a good circulation of fresh air throughout the whole of your greenhouse and hopefully lowering the temperature within the greenhouse as a result.
If your greenhouse doesn’t have louvre windows and you aren’t able to fit them, then the next best way to let air in is through the doorway – as this will be letting air in lower down to encourage air circulation.
What you may also find is that when temperatures are high, even with louvre windows and roof vents in use in your greenhouse you may still need to leave the greenhouse door open to let in the maximum of air.
Greenhouse Door
Your greenhouse will usually have a single or double door on one end of your greenhouse – or larger greenhouses might have a door on both ends which makes the flow of air through the interior of the greenhouse even easier.
The main purpose of your greenhouse door is to allow you access into the greenhouse when open and when closed to help keep unwanted visitors out – such as pets, birds, larger pests etc. - as well as keeping the weather out. But it’s secondary purpose can be a way of allowing air into your greenhouse.
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Throughout the summer months you may well find it necessary to keep your greenhouse door open all day – and depending on the temperature reached overnight, it may need to be left open then too. The best way to check what temperatures your greenhouse is experiencing is to use a max / min thermometer to record the highest and lowest temperatures reached. |
Top Tip
If you expect to have unwanted visitors making their way into your greenhouse via an open door – cats, dogs, and birds are obvious visitors, but you might also find mice, rats, hedgehogs, badgers, rabbits, and deer all finding your plants interesting – then you might want to think about adding a fly screen, mesh or other material over the doorway which will stop unwanted visitors but still allow air to flow in.
Roof Vents
With most greenhouses there are opening windows in the sloping roof, hinged along the ridge of the greenhouse. As standard these are usually designed to be manually opened, with a standard stay (similar to a house window) to keep them open or closed.
When you speak to any gardener, they will say that you can never have too many roof vents – you can always keep a roof vent closed but you can’t open one which isn’t there! So if you are purchasing a new greenhouse always check how many roof vents you are receiving as standard – and check if it’s possible to add more. Roof vents are incredibly difficult – if not virtually impossible – to fit into existing greenhouses.
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The reason for this is twofold:
- You need to get the roof vent from the greenhouse manufacturer – depending on the age of the greenhouse, the model you have may no longer be in production – and different manufacturer's roof vents will not be compatible.
- The greenhouse manufacturer may not sell roof vents on their own – the reason being that they are so difficult to fit retrospectively, often needing panes of the existing glass to be cut and the greenhouse roof would need to be dismantled before an extra vent can be added.
Typically roof vents will be approx. 2ft square (as usually glass greenhouses use 2ft wide panes of glass). Ideally, the opening vent area of your greenhouse should be 1/5th of the floor area.
For example: If you have a 6ft x 8ft greenhouse, the floor area will be 48sq ft. A 1/5th of this would be approx. 9-10 sq ft. If your roof vents are 4sq ft, you would ideally need two to three opening roof vents.
Side Vents
Although you will find with some models of greenhouses there will be opening windows – usually top hung – on the sides of the greenhouse, in the majority of cases when we talk about side vents in a greenhouse we are referring to louvre windows.
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Louvre windows are basically made up of horizontal slats of glass (or other glazing material) which are fitted one above another to create a slatted panel in your greenhouse. These slats are mounted so that either manually or automatically – with the addition of an autovent – they can be opened to allow air in to your greenhouse when required. |
Although thought to be less effective than roof vents, they are still a good way of increasing ventilation in a greenhouse and as they can be mounted at floor level, when combined with roof vents they create an effective way of moving air throughout your greenhouse.
Top Tip
What we like about louvre windows is that because they allow in less air than an open roof vent, they are a great way of ensuring fresh air can enter your greenhouse during the colder months without loosing too much warm air at the same time. Fresh air will ensure your plants have access to carbon dioxide for growth and will also help to prevent stagnant air pockets in humid conditions.
Increase Greenhouse Ventilation
If you have checked your greenhouse and ensured it has an adequate number of roof vents and louvre windows and that these and the door can be left open, then the next thing to do is to circulate air from outside into your greenhouse.
Fans
If you have electricity in your greenhouse, then you can easily and quickly do this by using fans. This could be done by using an Air Blower which has been designed for greenhouse environments and is specifically designed to efficiently ‘blow’ air around your greenhouse. Or it could be by using a greenhouse heater on a fan-only setting to move the air around your greenhouse.
The Air Blower shown opposite has been specifically designed for use in a greenhouse to improve air circulation. By improving airflow, this Air Blower will help to reduce condensation, ensure even temperature throughout the greenhouse and help to deter botrytis and other airborne fungal diseases. This Air Blower has been built to last – it has a stainless-steel casing and sealed motor for continuous running. |
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To ensure the most efficient positioning of this air blower it is supplied with hooks and chains so it can be hung from the roof of your greenhouse where the roof vents are situated.
Automatic Openers
Automatic openers can be fitted to both roof vents, side vents and louvre windows and they are designed so that when the temperature increases the vent / window is automatically opened and as the temperature falls, the vent / window is closed. This means that you no longer have to be available to open the windows – so you can be out at work, on holiday etc. and the windows will be opened and closed automatically.
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The automatic openers which we stock at Two Wests are manufactured by Bayliss. These vents operate using a wax filled metal tube. This mineral wax expands with heat and this pushes a piston to open the auto vent and in turn push open the window it is attached to. When the temperature drops, the wax shrinks and a strong stainless-steel spring closes the vent and resets the piston. |
Top Tip
The only thing to be aware of when using autovents is that it takes time for the wax to expand – it isn’t an instant action, the window will open gradually as the wax expands. So, to prevent any damaging temperatures within your greenhouse as these auto vents respond, ideally have other ventilation already open – such as manually opening any louvre windows and opening the greenhouse door.
Is Ventilating My Greenhouse Sufficient?
Although greenhouse ventilation is all about getting fresh air within the greenhouse, It's also important because it can help to reduce the temperature within a greenhouse during the warmer, sunny months.
Depending on the temperatures being reached within your greenhouse, throughout the summer you are likely to need to combine good greenhouse ventilation with greenhouse shading and humidity. It is only with the combination of all three of these that you will be successful in reducing temperatures to maintain a healthy growing environment for your plants.
Our blog post What Is The Best Way To Ventilate A Greenhouse? has been created from our personal knowledge and information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. If you have any queries you can contact us today!
Discover more from Two Wests from our blog to answer more gardening questions you may have. We offer tailored advice when it comes to shading your greenhouse and will help you discover if your greenhouse is too hot. Check out our Gardening Guides to help your plants flourish and thrive!