How to Protect Crops from Frost with Fleece Covers
Everything you need to know about how to choose the best fleece cover or fleece jacket for plants, trees, shrubs and crops. Ensure your plants stay protected from frost, cold, wind and harsh winter weather.
What is garden fleece?
Garden fleece - also known as horticultural fleece, frost covers or crop covers - is an insulating material placed over plants, shrubs, trees and crops to protect them from frost, wind and cold weather. They are used to cover vulnerable plants over winter, as shelter against late spring frosts and as a barrier against garden pests such as pigeons, blackbirds and squirrels. Fleece also allows you to plant out your crops earlier in the year - in most instances up to 2 weeks earlier than uncovered crops.
Why use a frost cover in the garden?
Fleece covers create an insulating barrier around tender plants and crops that prevents damage during the night as temperatures plumment. This being the UK, night-time frosts don't just happen over winter but can occur until May or even June and begin again in October, leaving many opportunities for frost to harm vulnerable plants. Unlike poly sheets, which are sometimes used to protect crops over winter, fleece is a breathable material, offering insulation but also ventilation to prevent plants from overheating and ensure healthy air culculation.
What kind of fleece is best for my garden?
As with everything garden related, there is no simple, catch all answer to this question and it really depends on your circumstances and set up. Many gardeners buy lengths of fleece by the roll - simple sections of horticultural fleece material - placing it directly over plants and crops or wrapping it around trees and shrubs. Others buy or make fleece covers that can be placed over fruit cages, cloches or grow tunnels to protect overwintering crops. Then there are fleece jackets that are designed to fit snugly over individual trees, shrubs or plants. And this is before we take into consideration the crucial issue of GSM count...
What is GSM fleece and why does it matter?
The insulating capacity of fleece is graded according to weight and measured in grams per square metre - or GSM. Put simply, the higher the GSM the "warmer" the fleece and the lower the temperature it will protect to. Light duty fleece is around 17gsm and will protect down to around -2c. Most plant fleece on the UK market is so-called 'heavy duty' fleece of between 30-35gsm, which is good to around -4c. Personally, when it comes to plant care in the UK climate, we feel the motto "better safe than sorry" applies, meaning all our fleece is either 45 or 50gsm to insulate plants and edibles down to -8c, giving an extra level of safety on really cold winter nights. On rare occasions you might see fleece jackets of up to 100gsm, though these are more of a specialist item and usually only necessary for things that would never normally grow in the UK, such as potted tropical plants.
What are the advantages and disadvantages of fleece covers?
Having read this far, you'd be forgiven for asking: Why not just buy a load of 100gsm fleece to cover every eventuality? Alas it's not that simple! First, plants need sun and the thicker the fleece the less sunlight can penetrate. Second, plants need air and ventilation to ensure general health and prevent pests and diseases, which can occur if humidity levels are high for long periods of time. Ultra thick fleece is less porous, leaving plants susceptible to diseases such as Botrytis and downy mildew without careful monitoring. From a practical standpoint, 100gsm fleece is more expensive, and with a thickness and heft that makes it more difficult to work with as a plant cover. For us, 50gsm fleece offers the ideal compromise, offering cold weather protection that takes into account the unpredictable and sometimes harsh UK climate but allows enough sunlight and air flow to ensure plant health.