How to fight the frost

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Plummeting temperatures call for a protective plan of action in your garden – and these tricks might save your plants this winter...

By Life is a Garden

home June 2011

It’s time to pull out your winter woolies – and pay careful attention to plants that will also need protection against icy temperatures and frost damage. The Highveld, KwaZulu-Natal Midlands and summer rainfall Karoo region regularly experience winter night temperatures below 0°C. However, frost is a very unpredictable and erratic climatic feature that is also influenced by other factors besides temperature.

During the night, both the soil surface and the air cools until water vapour in the air condenses on exposed surfaces – such as foliage and lawn – forming dew. When temperatures drop to below freezing, the water vapour turns into ice crystals known as frost. In winter, frost is most likely to occur on wind-free, cloudless nights as both wind and cloud cover can keep the air temperature warmer. In some regions the air is too dry for ice crystals to form but the below-freezing temperatures still damage plant structure; this is known as black frost – a term that refers to the colour of damaged plant foliage and stems. Frost damage occurs when the cell sap in plants freezes – this causes the sap to expand and the cell walls to rupture, thereby destroying the plant.

Gardening in frosty regions

To maintain a thriving garden, it’s essential that the majority of your plants are able to survive the coldest temperatures that occur, particularly trees and shrubs that form the backbone of your garden and take a long time to reach maturity. Make sure that two-thirds of these plants are evergreen so that the garden has foliage during winter; see what grows well in neighbouring gardens and get advice from your local nursery. Also investigate local indigenous plants, as these are perfectly adapted to prevailing conditions.

In a sheltering canopy of frost-hardy trees and shrubs, you can plant smaller shrubs and perennials that are somewhat less frost-resistant. Beds under north facing walls also have their own warmer micro-climate where you can experiment with your plantings.

To further widen your plant choice, bear in mind that many trees and shrubs can survive frost – provided they’re protected during their first three winters.

How to protect plants against frost

• Keep up with weather forecasts; visit www.weathersa.co.za.

• Apply a thick mulch over the roots of any plants that may be damaged by a heavier than usual frost.

• At night put hessian, straw tepees or a frost cover over plants that may be damaged by frost but open up at least one side during the day.

• Delay removing plants that seem to be destroyed by frost until the spring. They may simply be winter dormant, or may re-grow in spring.

• Delay removing damaged foliage until spring as it can act as protection against further frost damage.

• Irrigate in the morning rather than in the evenings so that the water is absorbed before temperatures drop below freezing.

ABOVE from left - 

1 this plant’s leaves have been damaged by frost but it’s best not to remove the foliage until spring as it can act as protection against further frost damage.

2 Apply a thick mulch over the roots of plants that may be damaged by a heavier than usual frost.

3 At night place hessian, straw tepees or frost covers over plants that are susceptible to frost.

4 frost damage occurs when the cell sap in plants freezes.

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