Brrrr, winter came early this year. Jack Frost has struck already, plunging the thermometer to a nippy -4 degrees Celsius and turning water trickling from the fountain into icicles.
What exactly is frost? (Coastal gardeners bear with me.) It’s a layer of ice crystals on a surface, formed from moisture in the air that condenses as the atmosphere cools, turning first into dew and then, when the temperature reaches zero degrees Celsius, into frost.
Many areas of the New South Wales coastal ranges, tablelands and inland experience winter frost. It usually occurs when a sunny day is followed by a clear night with no cloud cover to trap the warmth that radiates from the earth after sunset.
This is known technically as radiation frost, though NSW also sometimes experiences what’s known as “advection” frost, when a large, cold air mass suddenly moves in, often accompanied by strong wind. Don’t assume a windy day means your garden is safe from frost that night.
How does frost damage plants? The trouble arises when the sap within a plant’s cell freezes and expands, in the same way water in a freezer tray expands as it turns into an ice cube. The solid, swollen sap ruptures the cell wall, turning the plant tissue into mush.
Frost damage is usually fairly obvious the next morning, your precious plants looking brown and squishy, or blackish and somewhat dead. A frost-hardy plant that evolved to cope with this situation may look dismal on top but be fine underground, so never assume all is lost, always wait until spring – or even midsummer in the case of a large shrub or tree – for signs of recovery.
There are lots of ways to avoid suffering frost damage in your garden, the most obvious one being to choose the right plant for the right place.
A frost-hardy plant that evolved to cope with this situation may look dismal on top but be fine underground, so never assume all is lost, always wait until spring for signs of recovery.
Start off by getting to know your garden, as every plot has cosy corners and frost-prone patches. Trees are probably the largest structures in your garden, followed by your house, and the areas downhill from them are the most sheltered – few gardens are absolutely flat. Overhead structures like tree branches and pergolas help keep warmth in, as do hedges and large windbreaks. Water holds heat better than the ground, so areas around a pond are warmer at night. Then, choose the right plants. Don’t try to grow, say, a jacaranda or a poinsettia if you’re living at an altitude of 1000 metres. The US Department of Agriculture (USDA) has produced a chart dividing Australia into hot and cold climate zones and knowing your zone helps enormously when choosing plants. Plant labels usually include appropriate information.
Lastly, slightly tender plants can be protected with lightweight, horticultural fleece from your local nursery, or sprayed with Yates’ “Wiltnot”, a protective polymer that lasts for several weeks.
Frost isn’t all bad. It benefits some deciduous fruit trees and turns starch to sugar in parsnips. I’d rather have a frosty garden than a tropical one. Winter has its own beauty.
Diggers Club (www.diggers.com.au/) publishes the USDA climate zone chart.
