Do Greenhouses Work in Winter?

Greenhouses can serve a huge number of purposes, and so the answer to whether greenhouses work in winter really depends on how you plan to use it. 

They certainly can provide benefits, but the scale of these benefits depend on your individual set-up and how you intend to use your greenhouse. 

Let’s look at some of the more common questions surrounding this topic:

Do Greenhouses Stay Warm in Winter?

Greenhouses typically stay several degrees warmer than the outside air, even in winter. This is especially so if your greenhouse is located in a sunny position (such as facing south). In these situations sunlight hitting the greenhouse during the day causes the inside temperature to rise. Even at night, once the sun sets, some of this warmth will be retained. 

Of course, the amount of heat that is retained will depend on the material used to construct your greenhouse, combined with factors such as the intensity and length of sunshine it receives, and the ability of your soil to store this warmth. 

Broadly speaking, though, even an unheated greenhouse will stay warmer than the ambient outdoor temperature. In cold winters, however, this is likely to only be a few degrees – hardly what most of us would refer to as “warm”.

Many more sensitive plants may still struggle to thrive in an unheated greenhouse during the winter. Growth of even hardy plants is likely to be minimal, until supplementary heating is provided.

Do Greenhouses Need Heating in Winter?

Whether a greenhouse needs heating in winter will depend on your intended use. If your greenhouse is simply a place to shelter sensitive plants from the worst of the winter then no heating may be necessary. Some winter crops that will grow outdoors in winter will do even better in the protective confines of a greenhouse. 

More cold-sensitive plants, however, may at best refuse to thrive, or may even be at risk of dying. 

If you grow citrus plants, for example, and the outside winter temperature reaches freezing, then an unheated greenhouse may not provide enough protection to keep your plants healthy and vigorous.  

Whether a greenhouse needs heating really depends on what plants you plan to grow in it, and what you’d like those plants to grow. Half-hardy tropical plants are likely to require – or at least benefit from – some form of background heating. 

Hardy perennial plants that are just moved indoors to shield them from the worst of the winter weather are likely to be fine, laying dormant in their pots and containers until spring starts in earnest. 

Do Greenhouses Protect Plants in Winter?

Greenhouses can be very effective for protecting plants from the worst of the winter weather. They will help to keep torrential rain and snow from damaging plants. Colder temperatures, while still a consideration, tend to be less of an issue for plants housed in greenhouses. 

Perhaps the greatest benefit for plants kept in a greenhouse over winter is that their growing season can be greatly extended. 

Speaking from personal experience, many of my perennial plants start bursting into new growth as early as February when kept in a greenhouse, when their outdoor cousins are still a long way from showing their heads. 

Furthermore, plants can continue growing long into the fall, again long after outdoor equivalents have been killed off by poor weather. It is not unusual for me, even in a temperate climate, to still be harvesting beautiful crops of tomatoes and peppers in October, even November, thanks to my unheated greenhouse.  

If you want to make the very most of the summer season then a greenhouse which starts warming up quickly in the spring, and remains toasty-warm in fall, can be worth its weight in gold.

Do Greenhouses Keep Plants From Freezing?

Whether a greenhouse keeps plants from freezing will depend on your own personal circumstances. It goes without saying that a heated greenhouse is best for avoiding freezing conditions for your plants, but even an unheated greenhouse can increase your odds of success.

A number of factors can impact how successful your greenhouse is at preventing plants from freezing. For example a south-facing greenhouse will get much warmer, helping to keep frost at bay. 

The level of insulation in your greenhouse can also affect how prone it is to freezing. For this reason many gardeners in cold climates add a layer of greenhouse insulation to the inside of their greenhouse during the winter months. 

Raising plants up off the ground can also be beneficial, as it prevents your plants getting chilled from beneath if and when the ground freezes. 

This winter I have successfully kept some more sensitive plants alive and frost-free all winter, though outside temperatures rarely fell more than a few degrees below freezing. 

Do Greenhouses Get Damp in Winter?

Greenhouses can get damp in winter. This is a result of heavy winter rainfall, your plants transpiring, and a lack of ventilation. Such moist, stagnant conditions can pose dangers to your plants, as it is these exact conditions that mould and fungi favor. This can lead to the untimely death of some plants if not controlled.

Fortunately there are a number of ways to avoid such conditions. Assuming you have an unheated greenhouse, don’t be afraid to open the vents and doors on sunny days to help circulate the air. A standard rule of thumb that has worked well for me is to wait until temperatures rise above 5’C (‘F) before doing so. 

How you water your greenhouse in winter can also affect the moisture within it. Consider cutting down on watering your plants in the winter months, most of which will go into dormancy anyway. Less water placed into the greenhouse will mean less available to evaporate and cause damp conditions.

Carefully clean your greenhouse both in the fall before winter sets in, and again in Spring. This should help to reduce any fungal spores remaining in your greenhouse, and so keep your plants healthier for longer. 

Finally, if you find that your plants are being negatively affected by damp conditions in winter consider investing in a low-cost greenhouse heater. 

Increasing the internal temperature of your greenhouse will make it less appealing to fungal spores, so should help to keep your plants in perfect health. They can be easily purchased on sites like Amazon for a reasonable price so can be a worthy investment. 

Do Greenhouses Let You Start Seedlings Early? 

Possibly the greatest benefit of all of having a greenhouse in winter is that you can start planting seeds much earlier. Greenhouses tend to warm up quickly in the spring, which not only encourages perennial plants to spring back into action, but also encourages seeds to germinate. 

What’s more, once germinated, your greenhouse provides a safe and secure area for these seedlings to rapidly take hold. In this way, when the last frosts have finally passed, you’ll be the proud owner of some big, healthy plants ready to put out, so they can make the very most of the summer growing season ahead. 

Conclusion

Answering the question of whether greenhouses work in winter is a tough one. On the one hand they can protect your plants from excessive weather, tend to stay warmer than the outside temperature (particularly if insulated well) and can greatly extend your growing season. 

On the other hand, damp conditions can be a problem, and without suitable heating there is still a risk that your plants may stop growing, or may even be at risk of cold-damage. 

Greenhouses work well as a place to extend your growing season, start planting seeds early in the season, or to overwinter hardy perennial plants.

For those who want to keep growing cold-sensitive plants over winter you’re going to have to carefully consider heating, insulation and ventilation to see if you can make such a project work for you.