In the winter months, there may be less to do in the garden than there is during the spring, summer and autumn, but protecting your polytunnel structure and the plants within it from frost and snow should be a major priority.
Benefits of a Polytunnel in Winter
So, what difference can a Polytunnel make in winter? First and foremost, it will allow you to keep lots of crops growing right through the winter and into spring. And, on those cold, crisp days when the sun does show itself, the temperature in a Polytunnel will be wonderfully warm.
Don’t, however, make the mistake of thinking that your Polytunnel will be frost free! Cold is a problem in mid-winter even in a Polytunnel, and snow can be a problem too, but fortunately, there are ways you can prevent these things from damaging your precious crops.
What To Grow in a Polytunnel Over the Winter
One of the most important ways to make sure that your polytunnel remains healthy and productive over the winter months is to think carefully about what you choose to grow. Fortunately, there are a range of annual vegetables and perennial crops that will survive perfectly well in your polytunnel, even if you do not choose to use any heating. Annual crops that can survive in an unheated polytunnel over the winter (especially with a little extra protection) include:
- Cabbages, kale, Brussels sprouts and other members of the brassica family.
- Winter onions, leeks and garlic.
- Winter peas & broad beans.
- Turnips & other root crops.
- Asian greens and hardy winter lettuces.
Even if you did not get round to sowing/ planting any of these before the end of the growing season, you could still consider stocking your polytunnel with some perennial plants over the winter months. Winter is the best time to plant bare root fruit trees and shrubs, for example, which could also benefit from the protection of your polytunnel. You can find out more about what to grow in the winter in our guide.
Protecting Your Polytunnel From Frost
Preparing your polytunnel for cold weather is a simple but vital process. Here are some of the things that you should do now before it is too late:
Consider Methods for Heating Your Polytunnel
While an unheated polytunnel can still be used to grow a wide range of produce even over the winter months, you might like to consider heating your polytunnel. Now could be a good time to arrange a new polytunnel heating system to grow more tender plants, or to create an outdoors living area that you can use all year round. For example, you could consider:
- solar powered electric heating
- a rocket mass stove, or another eco-friendly solid fuel heater.
First Tunnels can offer several traditional polytunnel heater options.
When winter arrives, one of the key jobs in a polytunnel is often to take some measures to protect frost-sensitive plants. Heating a polytunnel can often prove costly, and is not always required. Before you go the whole hog and install a heating system, you might want to consider taking some of the following more sustainable options for increasing the temperatures in your polytunnel:
Add Mini Polytunnels, Row Covers or Cloches Inside Your Polytunnel
Protecting plants growing in your polytunnel from frost is often simply a case of giving them an extra layer of protective covering. You can consider using mini polytunnels, row covers, bubble wrap, horticultural fleece or other fabrics, or even simple cloches made from plastic food packaging to protect individual plants.
Improve Thermal Mass Before Cold Weather Arrives
Another way to give your plants a little extra protection from cold weather is to improve the thermal mass inside your polytunnel. This can help to keep your polytunnel a little warmer during cold winter nights. Stone or brick, concrete, clay or ceramics can all be used for paths, bed edges or staging in your polytunnel. You can also store rainwater inside your polytunnel. Materials such as these will catch and store the sun’s heat during the day and release it slowly once temperatures fall.
Water is also good at storing heat so you could consider placing a water butt for rainwater harvesting in your polytunnel, or creating a water garden in your polytunnel, such as a natural pond, barrel garden or fully fledged hydroponics or aquaponics system.
Mulch To Protect Plant Roots From Cold Weather
A polytunnel will keep plants warmer than those grown outside, but even so, in cold weather, the inside of a polytunnel can still drop below zero, which can cause damage to plants and their root systems. Another way to prepare and to keep roots warm is to cover them with a protective layer of mulch.There are a number of different mulches that can be used for this purpose, including:
- autumn leaves
Create a ‘Hot Bed’ for Cold Weather Warming
As cold weather approaches, another option that you could consider is growing some tender plants on a hot bed. Hot beds are beds built up with composting straw and other organic materials. As they decompose, these materials will give off a surprising amount of heat, which can help to keep cold weather at bay.
Keep Chickens in Your Polytunnel
If you keep chickens or other livestock within your polytunnel, the chickens themselves will add warmth to the structure. As well as helping to keep your polytunnel frost free, keeping chickens in there could also help to add fertility to your growing areas. Read more about keeping chickens in a polytunnel.
Protecting Your Polytunnel From Snow
As winter progresses, snow will often settle on a polytunnel, creating a layer of the white stuff. This snowy blanket has both advantages and disadvantages. So should you always knock off the snow? If you do need to get rid of it, how should you do so? Let’s take a look at this winter polytunnel problem:
Should I Always Get Rid Of Snow From A Polytunnel?
It is important to realise that snow on your polytunnel roof is not always a bad thing. Sometimes, snow can help to insulate your polytunnel and protect the plants inside from hard freezes. A soft accumulation of fresh snow can create a full layer on top of the plastic and make it warmer inside your polytunnel. It will act in much the same way as an igloo, which protects Inuit peoples from the extreme cold, or a snow shelter for stranded mountaineers. Sometimes, it will be a good idea to leave a fresh accumulation of snow overnight in order to take advantage of the insulation it provides.
If one or more of the following is true, you may wish to hold off on clearing off that protective layer:
- A hard frost and extremely cold temperatures are forecast overnight.
- Ice storms or hail are forecast in the immediate future.
- Strong icy blasts are due to blow in shortly.
However, snow on your polytunnel can also put strain on the structure. While fresh snow can be fluffy and relatively light, too much snow can stress the plastic covering and an intense accumulation could be too much for the structure. If the snow freezes onto your polytunnel, the plastic can be damaged. So if snow settles for too long, or is too heavy, it is best to remove it. A thick layer of snow on your polytunnel can also be a disadvantage when it is blocking too much light from plants growing inside it. Light levels can be a problem in winter at the best of times, so snow will often have to be removed when it has remained for too long and is keeping what little daylight there is from growing winter crops.
If one of the following is true, it is probably best to get rid of the snow in spite of the insulative advantages:
- Lots more heavy snow is forecast.
- There is already a particularly heavy accumulation of snow on your polytunnel.
- The snow has remained for several days.
How To Get Rid of Snow on a Polytunnel
If you do decide that the snow has to go, the good news is that this is a problem that is usually very easy to deal with. Often, snow will simply slide off as the temperatures rise inside, either due to sunlight or with the use of a polytunnel heater. Where it does not:
- Gently push on the inside of a smaller polytunnel to dislodge the snow that has settled above.
- Increase heating inside the polytunnel and it will melt off.
- Carefully take a long-handled broom or window cleaning brush and knock the snow off your polytunnel.
- On a larger tunnel, gently run a rope held by two people over the top to dislodge the accumulation. This is usually enough to dislodge any stubborn snow that still clings after using one of the other methods.
This winter, how are you going about protecting your polytunnel from frost, snow and other winter conditions? Let us know in the comments below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.