Cold weather, frost in particular, cause the water in plant cells to freeze damaging the cell wall. Frost damaged plants are easy to spot. Their growth becomes limp, blackened and distorted. Evergreen plants often turn brown and the leaves of tender plants take on a translucent appearance. The main source of trouble during the colder months, for even the hardiest of plants, is prolonged spells of severe cold when soil becomes frozen for extended periods.
During the dormant winter period, less hardy plants may succumb to frost or to cold and excessively wet soil. Leaves may become frost-bitten and roots can rot. So it’s important to protect your plants before first frosts strike to ensure the continued health of your plant.
The level of winter protection required depends on where you live and how exposed the planting area is. In sheltered suburban areas you may get away with not protecting tender plants at all. However, if you are going to experiment, do pay attention to weather forecasts – don’t get caught out by a sudden hard frost.
For general protection of your garden apply a layer of bark compost or mulch 5cm deep around herbaceous perennials but use grit around the plants themselves. This will stop moisture collecting and rotting the stems while the mulch will keep them warm. The mulch will also help by breaking down over the winter months, adding organic matter to the soil and improving drainage. This insulation will minimalise the freezing of the soil which can cause such damage to plants in the winter.
Mulching also does a great job in the summer, keeping the plant roots cool and reducing moisture loss from the soil.
Plants trained against walls or tender plants growing in the open can be protected with simple fleece-covered frames. Alternatively, sandwich a layer of bracken leaves or straw between two large sections of chicken wire and use this to cover plants during frosty evenings.
Tender bulbs, corms and tender herbaceous plants (that die back) should be covered with a thick mulch of manure, straw or old leaves to prevent the soil from freezing. In the spring, new shoots can be protected with a loose layer of straw or a bell-cloche.
Protect the crowns of tree ferns and insulate their trunks by wrapping them in layers of fleece or hessian stuffed with straw. Cordylines and palms in colder areas can be treated similarly by tying their leaves into bunches, to protect their crowns.
Choose outdoor containers that are frost-proof to prevent them cracking. Pots give you great freedom to move tender plants to sheltered areas in the winter or into a shed or greenhouse for protection. Those that can’t be moved should be placed on ‘pot feet’ to aid drainage. Using a light, free-draining compost with added perlite will also help with this. Insulate them with a layer of bubble wrap or hessian to prevent them freezing and cracking and ensure plant rootballs stay healthy.
Good practice to prevent winter damage
Choose plants that are reliably hardy in the area where you live.
Avoid high-nitrogen fertilisers early and late in the year as they encourage plants to make lots of sappy leafy growth that is particularly susceptible to frost damage.
Make sure tender specimens are planted in a sheltered spot, under large trees and shrubs or against walls. Give them some heat and protection during the winter.
Ensure that plants with tender flower buds or shoots are not planted in east-facing sites.
Leave the old growth of tender plants unpruned over the winter months. This will help to protect the central crown of the plant and take the brunt of any frost damage. If plants are cut back hard in autumn new growth could be damaged by frost.
Cold air and frost always descend to the lowest point in a garden so avoid planting tender plants in obvious frost pockets.
Well drained soil will prevent winter waterlogging. Frozen soil for prolonged periods is a big winter killer.