How do greenhouses work?

While it seems to make sense that your plants will grow more easily in a greenhouse, it might be nice to know exactly why that is!

When the sun shines on a greenhouse, the light is absorbed and divided over your greenhouse as heat energy. Glass, polycarbonate or foil is transparent for visible light and short wave light. The sunlight is being absorbed by the material of the greenhouse, the soil and the plants and is being transformed into heat energy. The materials that are being heated will transmit a long wave heat radiation and that’s how the temperature rises in a greenhouse.

While this explanation might be quite technical, it’s no different to how a room will heat up when the sun is shining on it. Because the greenhouse is made entirely out of glass the effect inside will be much larger than in a room with one or two windows. The heat and light will give your vegetables and flowers the energy they need to grow.

Next to the sunlight warming up the greenhouse, your plants are protected from outdoor challenges, such as frost, wind, rain and thunderstorms. Your plants are nice and safe in the greenhouse and you don’t have to worry about a sudden storm to ruin your crops.

Do greenhouses need ventilation?

In short… Yes! Especially during summer it’s important to pay attention to the temperature of your greenhouse. When you have a greenhouse in glass or polycarbonate, ventilation is needed to prevent overheating and the greenhouse becoming too humid. The easiest way to ventilate your greenhouse is by opening the windows or doors by hand, but you can also install a hydraulic system that opens the windows automatically. These can be found as of about 75 dollars and they are easy to install. These hydraulic systems will open the windows when the temperature rises above a certain level and will close them again when the temperature decreases. If you are working with skylights, it’s best to place them on the east side of the greenhouse, not subjective to the cold Northern wind and rain. During winter your greenhouse also needs ventilation, but then it will be mostly to prevent the humidity and should be done for short periods of time, while the sun is shining.
Tunnel greenhouses will automatically have a little wind flowing through, as they are not insulated as strongly as a glass or polycarbonate greenhouse.

When were greenhouses invented?

People have been experimenting with growing plants in controlled environments as of Roman times. Obviously these methods were very different from the modern greenhouse we know now, but the idea was already active in the mind of some enthusiastic Roman gardeners.

In the 17th century the concept of greenhouses started to appear more and more in England and the Netherlands. The 17th century greenhouses were still far from practical, the amount of work to close up at night or during winter was enormous.

The modern greenhouse as we know it, is often credited to the French botanist Charles Lucien Bonaparte. He built the first practical modern greenhouse in Leiden, The Netherlands, during the 1800s to grow medicinal, tropical plants.

The golden years of the greenhouses were in England during the Victorian era, where enormous glasshouses were constructed and the upper class built the most exquisite glass constructions.

Can greenhouses be used in winter?

People often ask us if a greenhouse will work in the winter? Off course it will! It’s up to you to decide what you want to use your greenhouse for. If you want to use it as a place for your summer and spring plants to survive winter, you will probably be ok by just insulating your greenhouse and keeping the frost out (unless you live in an extremely cold climate). If you however want to use your greenhouse to grow winter vegetables, you need to check which temperatures are necessary for your plants. You can do this by heating and insulating your greenhouse and by making sure you prepare your greenhouse thoroughly for the winter to come. Once again, the climate you live in is an important factor in this one, so think about what kind of temperatures your greenhouse will need to undergo when you decide how you will use and protect your greenhouse.

Will a greenhouse stay warm in winter?

This one depends on the climate you’re in. Can greenhouses grow plants during winter? Yes, they can but there’s a few things you need to pay attention to. The temperature in a greenhouse will in general be a couple of degrees warmer than outside, because when the sun shines on the glass op plastic, the heat will be held in the greenhouse. However during frost, there’s no guarantee that the temperature in your greenhouse will stay above freezing point. Luckily there are some steps you can take to avoid your crop from freezing. The most important one is to prepare your greenhouse for winter. If you live in a cold climate, it would also be a good idea for you to explore greenhouse heating options. This way you will be able to enjoy your greenhouse all year long!

Can greenhouses be used year round?

Yes they can! As long as you pay attention to the temperature (especially in summer and winter), your greenhouse is good to go all year long. Make sure you check for overheating during summer and for frost in winter. Depending on the climate you’re in, you might need extra heating or ventilation to prevent the greenhouse from becoming too hot or too cold. During spring and fall, temperatures will most likely be less extreme, so your greenhouse will need less checking and adjusting. Make sure you prepare your greenhouse for winter and take a look at insulation and heating options to guarantee a steady temperature!

Do greenhouses need to be heated?

Does a greenhouse need a heater to make sure you can keep growing in winter? There’s no simple answer to this one as it largely depends on the climate you’re in. If you’re in an area with lots of frost and snow and you want to keep growing vegetables or plants you will need a heating system to keep the frost outside. Make sure your greenhouse gets lots of sunlight, as this will heat up your greenhouse (also during winter) and will make the extra heating less necessary on sunny days. When you’re in a more moderate climate and there’s no or hardly any frost or snow, you can probably go without heating. In any case, whether you will use a heater or not, it’s always a good idea to insulate your greenhouse. When you heat it, the heat will be kept in the greenhouse more efficiently and without heating you can win a couple of degrees. The best thing to do is install a good thermometer in your greenhouse and check when you think it might be getting too cold. Take a look at the greenhouse heating options.

Why is a greenhouse called a greenhouse?

Greenhouses were originally referred to as botanical gardens. But since the term “greenhouse effect” has been introduced to describe the way a portion of the sun’s heat is absorbed by the earth’s atmosphere, which keeps our planet warm at night, there has also been a shift to the name of the currently known greenhouse. This is because the same process that warms up the earth also takes place in a greenhouse, where the glass structure will capture the sunlight and the area under the glass will heat up. That is why now greenhouse is the widely used term to describe these glass or polycarbonate structures.

Will a greenhouse keep plants from freezing?

Once again there’s no simple answer to this one, as it depends on the climate you live in. Is your winter harsh and long? Then you will probably need to foresee some extra measures to keep your plants from freezing. Is your climate more moderate and does it only freeze during a short amount of time and not very hard? Then you can probably get along by insulating your greenhouse and making sure it gets plenty of sunshine to heat up during the day.

The best way to make sure your plants are not freezing, is by installing a thermometer in the greenhouse and keeping a close eye on it. When the temperature drops below freezing point, you can insulate your greenhouse or add greenhouse heaters.

Can greenhouses get too hot?

Yes they can. During summer it’s important to monitor your greenhouse temperature (this can easily be done by installing a thermometer inside your greenhouse) and make sure it doesn’t get too hot. It depends on which plants you’re growing, but in general and in the average climate, the hottest summer days can be too hot for your plants to survive in. Luckily there are enough ways to bring the temperature down. You can choose to use a shade cloth to protect the greenhouse from direct sunlight and you can ventilate your greenhouse. The easiest way to ventilate your greenhouse is by opening the windows or doors by hand, but you can also install a hydraulic system that opens the windows automatically. These hydraulic systems will open the windows when the temperature rises above a certain level and will close them again when the temperature decreases.

Take a look at our article about greenhouse shade cloths, to help you cool down your greenhouse!

Does greenhouse glass block UV?

This depends on the material your greenhouse is made off. A glass greenhouse cover will block UV light, however the more common polycarbonate covers don’t always block UV. Some growers will choose a material that will allow UV light into the greenhouse, because this way it resembles the natural growing conditions. When you allow UV light to enter your greenhouse, you can benefit from the protected environment as well as the UV light similar to outside growing plants.

When you want to allow UV light during winter but not during summer, you can use shade cloths to block UV light in summer and make sure your plants aren’t harmed by a high amount of UV rays.

Does a greenhouse need to be in the sun?

What direction should your greenhouse face? Where to place your greenhouse is a big decision to take. Especially when you’ve bought a glass or polycarbonate model, it won’t be easy to move once you’ve positioned it.

You will usually place your greenhouse in a sunny place, with not too much wind and shade. If your greenhouse is placed in the shade, it will undermine the benefits of growing plants in a greenhouse, as sun is an important factor to heat your greenhouse. Depending on your climate, we would advise you to place the greenhouse either in a southern or western orientation. It also depends on what plants you want to grow and how much heat they need. Take a look at our greenhouse guide for beginners to get you started!

Does greenhouse plastic have to be clear?

We recommend you use clear plastic or glass for your greenhouse as this will give you the best result to transmit the sunlight into your greenhouse. When you use colored plastic, this will impact the amount of sunlight in your greenhouse. It’s better to use clear plastic and cover up with a shade cloth during summer, if necessary.

Does a greenhouse retain heat?

When the sun shines on a greenhouse, the light is absorbed and divided over your greenhouse as heat energy. The sunlight is being absorbed by the material of the greenhouse, the soil and the plants and is being transformed into heat energy. The materials that are being heated will retain their heat and transmit a long wave heat radiation which is how the temperature rises in a greenhouse.

While this explanation might be quite technical, it’s no different to how a room will heat up when the sun is shining on it. Because the greenhouse is made entirely out of glass or transparent polycarbonate, the effect inside will be much larger than in a room with one or two windows. The heat and light will give your vegetables and flowers the energy they need to grow.

Do you place a greenhouse indoor or outdoor?

Both are possible! While most people will place their greenhouse outside because it generally takes up a lot of space, you can also decide to place your greenhouse inside. It’s important when you do choose an indoor greenhouse, to make sure it receives plenty of light, a greenhouse in a garage will not work as sun as is the most important factor to help your plants grow. Especially the mini greenhouses or portable greenhouses are good options as indoor greenhouses.

Indoor greenhouses are usually only meant to grow some smaller plants and herbs, while outside greenhouses have very few limits. You can go as big or as bold as you like and enjoy fresh vegetables all year long!