A polytunnel is of course one way to protect your plants from the cold. A polytunnel will fend off the worst of the winter weather and, in some parts of the UK, will be perfectly sufficient to keep most common winter crops frost free.
But if you wish to grow more tender or even exotic crops, you may need to take more steps to keep your plants safe and protect your plants from the cold. Here are some other steps that you can take to keep your plants from damage or death if a sudden or particularly harsh cold snap arrives. These options may also open up a whole new world of possibilities and allow to you grow an even broader range of crops in your polytunnel.
Add Thermal Mass Inside Your Polytunnel
One of the very best ways to regulate the temperatures inside your polytunnel is to add thermal mass. When you add thermal mass to your polytunnel, it will stay warmer in winter, and will also help avoid high temperature extremes during the summer months.
Materials with high thermal mass are simply materials that are good at catching and storing heat energy from the sun. They will absorb heat during the day, then release it again slowly when temperatures fall (usually at night).
There are a number of ways to incorporate materials with high thermal mass into your polytunnel. For example, you can use them to make pathways or bed edging, to make staging, or other structures within the space.
Stone, concrete, brick and ceramics all have high thermal mass. Water does too. So keeping containers of water inside your polytunnel can help prevent frost from encroaching on the space during the night.
Create a Polytunnel Inside a Polytunnel
If you are interested in growing more tender or exotic plants in your polytunnel, a single cover may not quite provide the protection you require to protect your plants from the cold. Rather than heating the space, you could consider trying something different from the outset. You could create what is, in essence, a polytunnel within a polytunnel.
Add a second layer of plastic cover with an air gap in between will mean that the space stays warmer in the winter. But if you use clear plastic, this won’t block out too much light. Some gardeners have even tried a make-shift version of this idea, and lined the inside of a polytunnel with a layer of bubble wrap.
Provide an Extra Layer of Protection Above Plants
Of course, most of the time, a regular polytunnel cover is enough to shield relatively hardy plants from the cold. In most of the UK, it will be rare for temperatures in the polytunnel to drop below zero.
However, if there is a particularly cold spell, winter crops may suffer if they are not given a little extra protection in addition to the polytunnel itself. And of course extra protection will be essential for more tender crops.
You can purchase mini polytunnels. These are ideal to protect plants from the cold inside a polytunnel or outside in your garden. These and other row covers can be bought. But it is also worthwhile considering DIY options. If you only have a few plants to protect, making your own small row covers, bed covers or cloches can be a great idea.
For example, you can use food packaging – plastic bottles etc. to protect individual plants. You can also use other reclaimed and or natural materials to make frames that can be covered with bubble wrap or other scrap plastic – perhaps even with offcuts from your polytunnel itself.
To make the frame, you could for example use offcuts of plumbing pipes, or natural branches picked up or pruned from your garden. Other enterprising gardeners have come up with a whole range of other solutions – a mini greenhouse made from old CV cases, for example, or a clear umbrella or tent section refashioned into a cover for a small growing area.
Plants can also be covered at night with horticultural fleece, or with a scrap fabric that can serve the same purpose. For example, you may have some old bedding that could be used to cover a tender shrub, tender tree or other woody plant.
Shield the Soil To Keep Roots Frost Free
Often, plants will only suffer a little if frost reaches their leaves, and perennials may die back but remain alive below the soil. It is most important, however, that roots are protected. To shield the soil and keep roots frost free, it is a good idea to wrap something around pots and containers to protect your plants from the cold.
Plants grown in the soil or raised beds can be mulched to keep roots frost free. For example, you might use straw, sheep’s wool, or bracken for this purpose.
Create a Hot Bed To Protect Your Plants From the Cold
Another way to make sure plants don’t freeze is to plant them into a hot bed. A hot bed is a raised bed. You fill the bed, however, with straw/ manure or other similar materials. These generate heat as they break down. The gentle heat from below can keep a wide range of plants happy even when there is snow on the ground. And inside a polytunnel, a hot bed can be even more effective.
A hot bed can be surprisingly effective when it comes to growing more tender crops, and can also significantly extend the length of your growing season – keeping tomatoes, courgettes and other summer crops going well into the autumn and perhaps even beyond.
Consider Sustainable Heating Options for Your Polytunnel
Another way to protect your plants from the cold is, of course, to heat your polytunnel. There are a range of conventional polytunnel heaters to choose from. But you could also consider eco-friendly and sustainable solutions, such as solar or wood fired hot water heating, for example.
As mentioned, you can still grow a wide range of crops over winter in the UK in a polytunnel with no heating at all. But heating is something to consider if you wish to grow tender or exotic crops throughout the year.
Bring Very Tender or Exotic Plants Indoors
Finally, of course, there is always one final option remaining. If the polytunnel and other measures are insufficient to protect your plants from the cold, you could consider bringing them indoors. There is one key thing to think about. How will you make sure that the plants you bring indoors are not exposed to extreme drying, or extreme fluctuations in temperatures? It is important to choose the right place to position the plants you bring indoors.
These are just a few tips to help you decide how to protect your plants from the cold as winter approaches and cold weather sets in. If you have more tips to share, please do feel free to share them 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.
To get in touch, visit https://ewspconsultancy.com.