Frost, that nasty icy death on plants? Not necessarily.
Frost forms when water vapor becomes a solid. This happens when a surface of an area cools past the dew point, when this happens, the air gets so cold that water vapor in the air turns into a liquid, which in turn freezes and forms ice, frost or form.
There are different types of frost, however the frost that we experience and that your garden experiences, is called radiative frost or hoarfrost. If you live in Johannesburg, then you have definitely experienced this frost and the damage it can do to crops, fruits and flowers.
How does this frost damage your plants?
When the ice crystals form on plants, it ruptures the cells in the plant and can cause the leaves to blacken. While this may kill off some plants, other plants might only die back and recover will when the temperatures start to warm up again. Surprisingly there are benefits to frost, as winter chilling and cold fronts will help turn starch into sugar in deciduous fruit trees, and can disrupt the cycle of pests and diseases.
So how can you prevent frost damage?
Frost covers and cloths work well and are widely available at nurseries and hardware stores. These covers protect plants during cold nights by keeping them insulated, and because they are made of lightweight material, it will allow sunlight to penetrate and charge up the heat source for the next cold evening.
As odd as it may sound, watering the frost cover before the frosty evening and early morning, can produce an ice layer that will help insulate the plants further.
Watering in the evening time before the frosty morning will increase the heat given off by the soil. A good soaking the day before a cold night will provide your garden with enough moisture to protect your plants from feeling the full effects of the frost. Ensuring that you water when the temperatures reach higher than 4oC, will give the plant enough time to absorb the moisture before the cold sets in.
It is a fine balance when watering plants during cold temperatures, as too much can cause frozen leaves and damaged roots, and too little will cause the plant to lose its hardiness against the cold. And lastly take precautions for plants that will receive sunlight first thing in the morning, as frosted plants that thaw out too fast will also damage.
Knowing when and how much to water will determine how well your plants will do during the winter temperatures. It is always better and more cost effective to prevent than to cure.