Frost damage

It's very cold out at the moment with many parts of the country covered in snow or severe ice and although many plants we grow in our gardens are tough as old boots, frost, cold weather and cold winds can be fatal to some plants. Typical frost- and cold-sensitive plants include most summer bedding plants and annual herbs, such as basil.

Temperatures below zero will always affect tender and cold-sensitive plants – and sometimes even hardy ones during prolonged periods of cold, or if they are grown in containers. Frost and excessive wetness at the roots can be a fatal combination.

Symptoms

New leaves are most prone to damage, which can cause complete dieback on tender plants or just severe leaf browning or blackening. Excessive severe cold can also kill the roots of plants – especially when growing in very wet or waterlogged soil or compost.

Damage occurs when the water in plant cells begins to freeze and expand – damaging the cell and rupturing the cell wall. These plants become limp, blackened and often turn brown or slightly translucent.

During particularly long spells of very cold weather, even hardy plants and evergreens can become damaged when the soil becomes frozen and their roots are unable to take up water.

Treatment and control

If your plants are damaged by frost, there is still a chance that they will survive and become healthy again. However, trying to avoid frost damage in the first place is advisable.

If frost has damaged your plants, then:

• Cut back frost-affected stems to undamaged buds or growth points – this will encourage new growth.
• In the spring, once the risk of frost has passed, feed your plants to promote healthy growth.
• Smaller plants can be dug up and moved into a greenhouse or on a windowsill – often this will encourage a full recovery if the damage has not been too severe.

Try to avoid frost damage by protecting your plants when severe cold weather is forecasted:

• When buying pots and containers for your patio, ensure they are frost proof to avoid cracking. These will benefit from additional insulation from fleece or bubble wrap.
• Avoid planting tender plants in frost pockets – these are the areas that are lowest in your garden where cold air will descend.
• Mulch soils with bark, manure or straw to stop it freezing, causing root damage and preventing water uptake.
• Protect the crowns (central growing point) of ferns and palms with fleece or straw. Tie the leaves together to stop snow and rain freezing in these delicate growth points.
• Plant out tender plants when all risk of frost is over at the end of May or beginning of June depending on location.
• Improve drainage of soil to prevent waterlogging.
• Don’t feed plants in winter, as soft new growth is more susceptible to frost damage.
• Harden up slightly tender plants by feeding with sulphate of potash in early autumn.