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The Big Chill – frost protection

Tino Carnevale

Tino Carnevale

August 6, 2013

It’s easy for me to romanticise childhood memories of the crunch of frozen earth underfoot on frosty mornings. Walking out into the overwhelming stillness on the way to collect firewood from across the paddock was like entering a suspended landscape. The reality of course is that it was far from my favourite part of the day and I regularly tried to palm the chore off on my siblings, with little success.

Frozen Physalis

Frozen Physalis

Training vines in the Coal River Valley during the winter months is the kind the of job that people describe as character building. Riding my motorcycle to start work at 6am, exchanging the grip of the freezing handlebars for a pair of freezing secateurs, waiting for the first ray of sun to creep over the valley to thaw me out… These are memories I will cherish always.

Correa reflexa -  looks delicate but is tough as old boots

Correa reflexa – looks delicate but is tough as old boots

Frost is one of those environmental factors which can be devastating to both the garden and the gardener. Those who live in frost prone areas will have dealt with losses somewhere along the line and in certain years no matter how well you know your garden we can still get caught out.

Frost occurs when solid objects, like the ground, get colder than the freezing point of water and the moisture in the air turns to ice and settles. When this happens to tender plant tissue, the water inside the cell structure swells and then ruptures as it melts.

In my experience there are many varying factors that dictate how frost will effect a plant. Some of these are soil type, site aspect, moisture levels, areas of greater thermal mass, shelter and of course the type of plant. Even the slope of the land will play a role.

If your area suffers from regular frost it will dictate how you garden. There is no blending of the seasons and this means few crossover crops. The first big frost spells the end of the autumn harvest and the beginning of planting your winter crops; the last frost signals the time to start preparing for the warmer months.

For example, down here in the south the rule is plant your tomatoes after Show Day (near the end of October). These crosses between urban legend and local knowledge help protect seedlings from the tail end of winter all around the country.

There are many ways you can go about protecting your plants from the harmful effects of frost and like with everything in gardening, you might need to use a combination of techniques to get the best outcome.

The most basic form of frost protection is to design you garden in a way that uses hardy plants to shield those that are more vulnerable. You can also utilise the thermal mass of large rocks, brick walls and bodies of water that will heat up during the day and retain the warmth at night.
Water holds it temperature extremely well so watering the night before a big frost is due can help prevent the frost from settling on that area.

Broad beans unperturbed by the frosty goings on

Broad beans unperturbed by the frosty goings on

Glass cloches are great but expensive, a plastic bottle with the bottom cut off certainly doesn’t have the same insulating or aesthetic qualities but does offer some level of protection.

For larger plants or groups of plants, simple structures made of bamboo poles and hessian are very effective although something as basic as some sheets of newspaper or an old shirt thrown over the plant will work in an emergency.

Applying potassium fertiliser helps to harden up the plants by thickening the cell walls, allowing them to withstand greater fluctuations in temperature.

If you do have a plant that has been damaged by frost, resist the urge to clean up the burnt outer leaves as it is best to leave them so they can protect the inner, unaffected growth. Wait until the danger is over to cut back the plant if needed.

Frost is usually thought of as a destructive force but it definitely has a lot of positive effects in the garden. Kale is always best harvested after a frost as the flavour is intensified and a lot of fruit and berry crops need periods of winter chill to produce well the next season.

Dreaming of next season’s delicious blueberries may keep you a little warmer the next time you’re having to work in an icy landscape.

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Catherine Stewart
10 years ago

I’m amazed that Physalis manages to shrug off such a frosty overcoat. What are your thoughts on mulch for frost protection? Good or bad?

Julie Thomson
10 years ago

Thanks for the post, Tino. Even here in sunny Queensland, we have areas that suffer frost, and on our property, the dips towards the creek have a palpable lower temperature in late afternoon and evening…. glad to receive good information about not taking off the burnt outer leaves of a plant when it occurs. Interesting about broad beans being so hardy and frost resistant, too.