Polytunnel gardeners can grow a wide range of produce over the winter months. A polytunnel provides a level of protection from the elements, and the vagaries of the UK winter weather. But in a cold snap, a polytunnel alone in not always sufficient to keep out the frost entirely, especially in more northerly reaches of the UK. Tender plants can be protected by means of polytunnel heating, or extra protection such as mini polytunnels, cloches, bubble wrap, fleece, or mulches such as straw. But while some plants will need protection, others will actually benefit from a little cold. Some vegetables taste better after a frost.
Vegetables that taste better after a frost or two include:
- Brassica – such as kale, cabbages, Brussels sprouts etc…
- Root vegetables such as carrots, parsnips, turnips, swedes, etc…
- Other leafy greens like Swiss chard.
Why Some Vegetables Taste Better After a Frost
The processes by which a hardy plant feeds and sustains itself through the tougher winter months are the same processes which make some vegetables taste better after a frost. Plants produce sugar, as well as oxygen, during photosynthesis.
Carbon dioxide and water are taken in and sunlight is used to convert these to starch – how a plant stores its energy. Enzymes then convert this starch to sugar, as part of the process of protecting themselves from winter cold.
A frost triggers certain hardy plants to produce more sugar. These higher sugar levels protect the plants. Metabolising these plant sugars helps plants to ‘stay warm’. The accumulation of sugars also decreases the amount of ice that forms in plant cells and can protect the cell membrane from freezing.
The conversion of starches to plant sugars is the reason why certain vegetables will taste better after a frost, as the plant sugars contained within the leaves or roots will make them sweeter.
Of course, not all vegetables can cope with a frost. There are plenty of things that you can do as a polytunnel gardener to protect plants in your polytunnel and give them a little extra protection if the temperatures are forecast to be extremely cold. But while it is important to make sure that those plants that require it are given protection from frost, it is also worthwhile remembering that there are some vegetables that will taste better after they have been exposed to colder temperatures.
Do you wait until after the frosts to harvest some of your vegetables? Do you find them sweeter later in the season? Let us know what your own experiments in your polytunnel have shown you in the comments below, and also feel free to share any comments or suggestions for how to use such produce in your kitchen. What are your favourite recipes for vegetables that have been sweetened by a few frosts?
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.