Frosts in most areas around New Zealand are just a fact of life. Although it probably doesn’t feel like it when one has hit you, they can be beneficial to the garden. Frost is an invaluable aid in the control of insects by halting the breeding cycle of a lot of general garden pests.
Of course frost can cause widespread destruction and your first line of defence is to get to know the weather so you can protect your plants. Watch for clear, cold, windless nights they usually mean a frost is in-bound.
Covering plants that are susceptible to frost is the easiest protection of all, like giving them a blanket at night. There are a variety of materials that you can use for covers, frost cloth, newspaper, and muslin. Even an old set of net curtains clipped together with clothes pegs. Try to keep the cloth away from the foliage using garden stakes to form a cage above the plant.
Frost cloth is available in most garden stores; it is lightweight and not very expensive. Made out of a spun polypropylene it will last for years, just make sure that you dry it fully before putting away for the season so it doesn’t grow mould.
Pre-made tunnels or cloches are perfect for protecting the vegetable garden. Tunnels are used as a mini greenhouse for the beginning of the season but they can also double up as frost protection. These tunnels can be purchased either in polythene or fleece, both will work very well.
If your garden does get frosted then the damage on plants especially on tender plants becomes obvious fairly quickly. Shoots and leaves will often go black or brown and then turn mushy. The frost has basically destroyed the cell structure of the plant and these frosted parts need to be removed by pruning.
There is one theory that some gardener’s use when a frost has hit, it involves leaving the frosted parts on the plant. When you do this any new growth is held at bay until all the severe frosts are over therefore not risking any new growth again.
Try using a cross between the two theories; on the hardier shrubs that have been frosted leaving the damaged parts of the plant and removing it later will be fine.
In the vegetable garden be a little fussier and remove most of the damage then replace the plant if necessary. Best practice is to always cover your plants to protect them from future frosts. Often tender seedlings become just too damaged to grow properly, it is better to start again with new seedlings.
A good rule of thumb is that it is better to be safe than sorry and cover when there is even with the slightest suspicion of a frost. The covers go on early evening and are removed first thing in the morning.