For gardeners in many parts of the country this will never be a problem, but for those living in frost prone areas heavy frost can be a very disappointing event every year or every few years.
Just like disease, the best method of dealing with it is to know what varieties are susceptible and to only grow the resistent varieties. However if you are only affected by a bad frost every few years then a system of protection may be the answer.
The first thing to understand about frost damage is that it occurs when the air temperature drops below zero causing water to freeze in the plant tissue rupturing the cell walls. However, there is also another type of damage that can occur after cold nights even when the temperature does not drop below zero, and that happens after sunrise when the sun and drying breezes desiccate the foliage as a result of reduced sap flow.
It is this second type of damage that can be minimized by the various "Frost protection sprays", but quite often the marketing hype tends to overstate their usefulness. Likewise, the old cure of watering the plants before the sun gets on them works in a similar way, but in any case, during a real frost the water will freeze in irrigation pipes and hoses if not kept moving, making this quite impossible.
The only systems which will minimize real frost damage must somehow keep the temperature of the plant's tissue from dropping significantly below zero for the whole duration of the frost. This may be from midnight onwards or even earlier.
In "radiation" type frosts, which are the type experienced in most of Australia, the frost is caused by a cold layer of air sinking during the night, so any cover which will impede this sinking will help reduce frost damage. Impervious materials such as plastics are best but materials like shade cloth and even larger trees will give some limited degree of protection. Materials used for this purpose however should not come into contact with the foliage.
Growing plants close to buildings can also minimize frost damage because of the residual warmth emitted by the building and warm air trapped around less open spaces. Similarly the local topograpy of the land can have a considerable effect as cold air masses on very still mornings, if unimpeded by building or vegetation, will behave much like a liquid and run downhill away from some areas and towards others. At other times however this tendency may be overpowered by a slight wind drift coming from the south.
For larger areas of plants in the open various strategies of frost protection are used. However, the method we recomend as the most practical for home gardens is covered in our following article:-