Frost can do a great deal of damage to garden plants and lawns. If you live in a frost-prone area, such Gauteng or the Free State, it’s a good idea to know how to predict it and take steps to protect your garden.

What is frost, and when does it occur?

Frost forms when night-time temperatures go below 0 degrees Celsius on cloudless, windless, nights.

You can get two kinds of frost: White and Black frost
  • White: This kind of frost forms when there is enough humidity in the air to create dewdrops (called ‘reaching dew point’). When then temperature drops below freezing, the dew drops freeze into ice crystals.
  • Black:  is the most damaging kind of frost. This occurs when the air is very dry. Without sufficient humidity to reach ‘dew point’, the cold causes the water inside your garden plants’ cells to freeze instead. This breaks the cell walls in leaves and delicate stems, turning them black – hence the name ‘black frost’.

White frost is less damaging because it does not cause the water inside plant cells to freeze; the ice insulates the plant sufficiently to prevent it – the same way an igloo can provide warmth. However, it can still damage or kill plants that are not cold hardy and turn your lawn brown.

You can’t stop frost, but there are some steps you can take to save your garden plants and lawn.

  • Keep tabs on the weather – looking out for below freezing night-temperature with low humidity.
  • Water your plants and your lawn in the mornings rather than evenings. This is so that the plants have had time to absorb excess water that might freeze at night.
  • Increase humidity around tropical plants with straw or bark mulch. This helps the soil retain moisture. It also increases the soil temperature to protect roots and bulbs. This is especially important for tropical bulbs. The leaves can be allowed to die back in winter, but as long as the bulb is protected, the plant will survive to regrow in Spring.
  • Cover young trees and other saplings with hessian or burlap. Cover the plant completely at night. You can leave the cover on during the day, but open up one side for airflow.


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