The short version: Frost protection comes down to two things: shielding tender plants on cold nights, and matching your crops to your climate zone. Cover frost-tender plants overnight, water the soil beforehand, and keep them in your warmest spots. Frost risk ranges from little or none in the tropics to regular in cool and alpine areas. Choosing hardy crops and raising seedlings under cover can stretch your season at both ends.
Winter does not have to be a dead stop for the veg patch. With a little planning, you can carry crops through the cold and get a head start on spring. The trick is knowing how frost behaves: a frost that flattens basil in Orange may never touch a courtyard in Cairns.
How frost forms, and why it matters
Frost forms on clear, still nights when the ground loses heat to the open sky and the surface drops below freezing. This is a radiation frost, the most common type in Australia, per the Bureau of Meteorology.
Cloud cover and wind both reduce the risk: clouds trap escaping heat, and wind mixes warmer air down to the surface, so the dangerous nights are the calm, cloudless ones. A clear, still evening is the cue to act.
Cold air is heavy, so it slides downhill and pools in low spots. These are frost hollows, and a dip can frost while higher ground nearby stays clear. A ground frost can also form before the air reading hits 0°C, since the weather-station thermometer sits over a metre up, so a screen reading near 2°C can mean the surface is near freezing.
Warm spots and cold spots in your garden
Every garden has microclimates, and using them is one of the cheapest forms of frost protection. A wall, fence, paving or tree canopy can hold enough warmth to keep the worst frost off nearby plants.
A brick or stone wall that catches winter sun soaks up heat by day and releases it slowly overnight, so tender plants tucked against a north-facing wall often come through a frost that nips the open beds. Spots under eaves or a canopy stay warmer too. A frosty morning shows where the frost lingers and where it never settles. Save those spots for tender plants, and put hardy crops out in the open.
Covering plants and other overnight tricks
Covering plants on a frosty night works by trapping the heat rising from the soil. The simplest cover is frost cloth or horticultural fleece, but hessian or an old sheet does the job too.
Hold the cover off the foliage on stakes or hoops, and bring it to the ground to seal in the warmth. Leaves pressed against the cover can still get frosted, so that small gap matters. The easy job to forget is the morning one: lift the cover once the sun is up, so the plants do not cook.
A few other moves help:
- Watering the soil in the afternoon can lift overnight temperatures a little, since moist, firm soil holds more heat than dry, loose soil.
- A good layer of mulch can help protect the roots.
- Pots can be shifted under cover or against the house for the night.
It is best not to overstate this. A cover can lift the temperature around a plant by a few degrees, often enough to save tender growth, but no guarantee in a hard frost.
Stretching the season at both ends
Season extension means getting crops growing earlier and later than the open garden allows, mainly by raising seedlings under cover and protecting plants once they are out.
Start seedlings on a sheltered windowsill, in a cold frame or in a glasshouse, so plants are ready the moment conditions suit, then harden them off before planting out. Our guide to starting seeds indoors walks through the steps. A glasshouse, polytunnel or cold frame holds warmth and keeps frost off, but vent any closed structure on sunny days.
One feeding note. Avoid pushing soft new growth with heavy nitrogen late in the season, since soft growth is the most frost-tender. A gentle seaweed solution is kinder than a big nitrogen hit.
Which crops shrug off frost, and which do not
Some crops take frost in their stride, while others can be cut down by a light cold snap. As a rule, leafy greens and cool-season crops are hardy, and summer fruiting crops are not:
- Hardy: many brassicas such as broccoli, kale and cabbage, plus broad beans, peas, garlic, onions, spinach and silverbeet. A light frost can even sweeten some.
- Tender: tomatoes, capsicum and chilli, basil, climbing and dwarf beans, and cucurbits like pumpkin and zucchini. These need frost-free conditions.
Hardiness varies by variety and by how hard the frost bites, so treat the list as a guide. Where frost is a regular visitor, lean into hardy crops through winter; browse the vegetable seeds range for cool-season growing.
Frost protection by Australian climate zone
Frost risk swings widely across Australia, so the right approach depends on where you garden. In short, the further south and the higher you are, the more frost matters.
In the tropical north, around Darwin, Cairns and Townsville, frost is effectively a non-issue, and the cooler dry season is prime growing time. In the subtropics, from Brisbane to Coffs Harbour, winters are mild and most gardens grow through with little to no frost.
Temperate gardens, such as Sydney and Melbourne, are where microclimate rules, since frost comes and goes by the spot, and Canberra sits colder again. Cool and alpine areas, from the southern tablelands to Orange and Stanthorpe, get regular, harder frosts and a short season, so hardy crops and season-extension gear matter most.
In Mediterranean zones, including Perth and southern Western Australia and Adelaide, winters are mild and wet, which suits winter sowing, and frost is occasional and mostly inland. Arid and semi-arid areas, like Alice Springs and Mildura, run hot days but cold, clear nights, so frost is a real winter risk.
Frost is far less daunting once you understand it: most often a clear-night event you can plan around rather than fight. Use your warm corners, cover the tender plants, and work with the cold.
Frequently asked questions
What is the easiest way to protect plants from frost?
Cover tender plants overnight with frost cloth, hessian or an old sheet, held off the leaves and brought to the ground. Water the soil that afternoon, since moist soil releases more heat overnight, and lift the cover in the morning so plants do not overheat.
Does covering plants really stop frost damage?
It often helps, but it is not a guarantee. A cover traps heat rising from the soil and can lift the temperature by a few degrees, usually enough on a light frost, though a hard frost can still cause damage.
Which vegetables can handle frost?
Many cool-season crops are frost-hardy, including kale, cabbage, broccoli, broad beans, peas, garlic, onions, spinach and silverbeet. A light frost can even improve the flavour of some. Tomatoes, capsicum, chilli, basil, beans and pumpkins are tender.
Do I need to worry about frost in Perth or Brisbane?
Mostly no on the coast, occasionally yes inland. Coastal Perth, the south-west WA coast and the Brisbane area have mild winters with little to no frost. Inland southern WA and low-lying spots can still get the odd frost.
What is a frost pocket?
A frost pocket, or frost hollow, is a low spot where cold air pools on a still night. Cold air is heavy, so it drains downhill and settles there. These spots frost more often than higher ground, so keep tender plants out of them.
Ready to plant? Browse our Vegetable Seeds.