How to protect plants in winter
Many plants struggle to cope with low winter temperatures and frost. You can judge what your plant can withstand by finding out how hardy it is – ie what temperatures it can survive. Hardy plants will withstand most winter temperatures, frost hardy plants can cope with a bit of frost (down to about -5°C) but plants which are half hardy or tender can’t remain outside if temperatures will be below 0°C, or at least they can’t without some protection.
Early flowering plants, particularly fruit trees, may also need protection from late frosts which can damage the flower buds and blossom.
Careful planting will minimise the need for winter protection. Ensure you identify any frost pockets in your garden and avoid planting anything but the hardiest plants there. If you have plants which are likely to suffer in harsh winters, then plant them in more sheltered positions, such as in front of a warm wall or in a sunny spot.
Depending on the plant protecting it over winter might involve just covering it when a particularly hard frost or snow is forecast, but more tender plants (such as cannas) will need to be protected all winter. If the plant is in a pot or is small enough to be dug up, and you have a heated glasshouse or conservatory, then you can simply move the plant indoors for the winter. Summer flowering bulbs, tubers, rhizomes and corms can be dug up and dry stored in a frost free place. If taking the plant indoors isn’t an option, then you will need to protect it ‘in situ’ outside. While protecting plants outside should give them a good chance of survival, it doesn’t guarantee they will survive, particularly if they are young or have been weakened by pests or disease. If the plant is very tender then you should consider whether the great efforts you will have to go to to keep it alive in the winter are really worth it, unless you can keep it indoors with heating.
There are many different ways to protect plants which are left outdoors over winter, below we outline some of the main methods.
Wire and straw
This is an excellent method for protecting small trees, shrubs and grasses, including banana plants and cannas which require permanent protection over the winter. A framework is constructed around the plant using wire mesh (‘chicken wire’). If the plant is large, then stakes can be hammered into the soil (taking care not to disturb the roots) and the mesh attached to them. This mesh cage is then stuffed with straw, ensuring that all parts of the plant are behind about 30cm thickness of straw. Pack more straw on top of the plant then tie some fleece, hessian or polythene over the top to prevent the straw flying away. Hessian sacking can be used as an alternative to the wire framework, with string tied around it to keep it in place around the straw, however this can be more fiddly to set up than a rigid wire cage.
Sheets of transparent, insulating material such as glass or polycarbonate can be used in a range of situations. Over beds, particularly alpine beds, sheets can be placed on bricks (to allow airflow underneath them) to provide insulation and frost protection. If using glass it should be well supported and any snowfall brushed off it to reduce the risk of it breaking.
Alternatively these materials can be used to create vertical screens to protect tender, wall trailed fruits or climbers. A wooden frame is made to so it will sit at an angle, the top attached to the wall and the base a short distance from the foot of the plant. The ends are left open to allow air flow around the plant. The frame can then be clad in the required material. Fleece or a breathable weed matting could be used as alternative covers. If you wish, straw can be stuffed behind the shelter to provide the plant with further insulation.
Horticultural fleece provides a simple way to give plants some minimal winter protection, for example for frost hardy plants when particularly cold weather is forecast. Fleece can laid over soil and pegged down, or wrapped around a plant and tied in place with string around the stem. This is a good solution, for example, to use to protect the blossom on small fruit trees when a late frost is forecast. The ease of applying and removing the fleece makes this a good temporary protection solution.
Bubble wrap can be used instead of fleece and will provide slightly more insulation. However, it will prevent air reaching the plant and should only be put on plants for very short periods (eg overnight).
Large perennials which die down in the winter can be used to provide their own protection, by removing large leaves and placing them over the crown of the plant as insulation. Gunnera, for example, can be protected in this way. For extra insulation, pack straw around the plant before placing the foliage over it. A few hefty sticks should be enough to keep the leaves in place.
These simple structures, usually clad with glass, plastic, fleece or polycarbonate, are a quick and easy solution to protect plants. Simply place the cloche or cold frame over the plant. They can be used throughout winter, or just put in place when a particularly hard frost is forecast.
A snow frame is a V shaped structure, usually made from wood or plywood boards, which fits over the plant and protects it from snow fall. To make a snow frame simply take two squares/rectangles of wood, fix them together to make a right angle, and affix a strap or thin strip of wood across the wider sections of the V on each side to hold it in place so it won’t buckle under the weight of snow. The frame is then just placed over the vulnerable plant to prevent snow falling on it.
Herbaceous perennials which die down in the winter can be given some extra protection by mounding up extra soil or mulch on top of the crown. A depth of around 10cm should be sufficient to keep them snug in the worst of the weather.
Here are some examples of protection methods: