Map your Frost in Winter

The biggest frosts follow clear wind-free nights. We can expect some good ones next week, as this rainy spell clears up.

Frost reaches its peak at that magical time when dawn has achieved full daylight, but no rays of sunlight have yet touched the ground.

That is when you need to be out there in your ugg boots and beanie (and perhaps some other garments in between, if you feel the need), to see just where it lies, and where it doesn't.

People who live in areas well-known for hard frosts are often surprised to find just how many frost-free patches there really are in their own gardens, (or on their larger properties). Mapping the frosts often reveals that we can grow many more frost tender plants than we thought we could. It can also mean that the cost and work of covering tender plants might not be really necessary.

If you carry a handful of stakes and a hammer, on your morning walk in the frost, you can mark frost-free spots where little plants will thrive. Plan your spring plantings as you go.

Frost flows downhill like a river. It is diverted by obstacles in its way, and it pools in hollows and above barriers. You may find quite large frost-free areas downhill from these barriers.

As well as this, every tree and shrub has a little frost free "aura" around it. It is smaller on the uphill side and larger below.  You might choose to plant under the tree, but note that the aura is larger than the its canopy. If root competition might be a concern, take advantage of the aura's outer edges.

Structures also have frost-free auras, though to a lesser extent.

While planning this year's spring plantings, you might also look for places to create frost shelters for the future. These can be rows of the frost-hardiest species. They can be as simple as a row of those tough matrushes, Lomandra longifolia, or a taller barrier perhaps doubling as a hedge, screen or windbreak. They are particularly efficient as frost-breaks if  they are bow-shaped and placed across the direction of frost flow with the centre of the bow uphill from the ends. This diverts the flow outwards, creating a sheltered nook to be filled with tender plants in a few years' time.

Forests and shrublands tend to hold the day’s warmth overnight. In our part of the world, ground temperature in these environments is always above freezing point and frost tender plants grow in them with no trouble at all. Restoring damaged ecosystems with their full range of original species can be a problem where clearing has thrown the area open to frost. A skeleton planting of pioneer plants to fill the clearing with a frost-free aura is a sensible first step. A serendipitous result can be that longer term species from the surrounding ecosystem don’t even need us to plant them. Changing the microclimate lets nature do the job for us.

With time and careful planning, it is possible to eliminate frost over large areas.