What to Do Before the First Frost: a UK Checklist

The first frost of autumn is the night the garden changes. Tender plants that were cropping happily the day before can be black and limp by breakfast. The good news is that almost everything you'd lose to it can be saved with a few hours' work in the weeks beforehand.

This is a checklist for those weeks. Work through it in roughly this order and nothing will catch you out.

1. Know when frost is due

Two things tell you when to act. The first is your region's typical first-frost window, which you'll find in the frost date checker. That gives you the season: the weeks when frost becomes likely.

The second is the forecast for the next few nights. Frost forms on clear, still nights, when the ground loses its warmth straight up into the sky. Cloud acts like a blanket, and wind keeps the air mixing, so a cloudy or breezy night is far less likely to bring frost than a calm, starry one. When the forecast says clear skies and light winds as autumn deepens, that's your cue. We never forecast here; the Met Office forecast is the place for that.

Frost also gathers in low spots. Cold air is heavy and runs downhill, so the bottom of a slope or a hollow by a fence (a frost pocket) gets frost earlier and harder than the rest of the garden. If you know your garden has one, treat it as being a few weeks ahead of everywhere else.

2. Pick tender crops

Tender crops are the ones a frost kills or spoils outright: tomatoes, chillies and peppers, courgettes and marrows, French and runner beans, sweetcorn, cucumbers outdoors, squash and pumpkins, and basil. If you're not sure which group a plant falls in, hardy or tender? sorts the common ones.

• Tomatoes. By the first frosts, which are often early to mid October in much of the UK, pick everything that's left, ripe or green. Green and part-coloured fruit will finish ripening indoors in a paper bag with a ripe banana or apple. Why tomatoes won't ripen explains the trick.
• Chillies and peppers. Pick the fruit. If you'd like to keep a favourite plant for next year, cut it back and bring it in before the frost: see overwintering chillies.
• Courgettes, beans and sweetcorn. Pick whatever is usable now. The plants are finished once frost touches them, so there's no point holding back.
• Squash and pumpkins. Cut them with a length of stalk and get them under cover to cure before frost reaches them. Storing winter squash covers curing.

Once a tender plant has been frosted, clear it. Blackened leaves rot quickly and give slugs and disease somewhere to hide.

3. Lift and store

Some crops are happy to stay in the ground through frost; others need lifting.

Leave in the ground: leeks, parsnips, kale, Brussels sprouts, swede and winter cabbage stand outside through winter. Many taste sweeter after a frost. Lift them as you need them.

Lift and store: maincrop potatoes, carrots and beetroot keep better indoors, especially on heavy, wet soil where they'd be at the mercy of slugs and rot. Store only sound, dry produce: one damaged root can rot its neighbours. Storing your harvest explains clamping, damp sand and curing.

Dahlias are the exception to "do it before the frost". Leave them until the first frost has blackened the leaves, then cut the stems back and lift the tubers. Overwintering tender plants walks through it, along with pelargoniums and fuchsias.

4. Get your covers ready

You don't want to be hunting for fleece in the dark. Before the first frost:

• Find your horticultural fleece, shake it out and check for tears. A torn sheet still works, but a big hole lets the cold straight in.
• Gather cloches, and check the cold frame lid closes.
• Find pegs, bricks or stones to hold fleece down. A loose sheet blows off just when it's needed.

On a frosty night, throw fleece over tender plants and young seedlings before dusk, so it traps some of the warmth the ground has held during the day. Take it off again in the morning once the frost has gone, so plants get light and air. How to protect plants from frost compares fleece, cloches, bubble wrap and cold frames and explains when each one works.

Hardy crops don't need covering. Save your fleece for what will actually suffer.

5. Move pots

Plants in pots are more exposed than the same plants in the ground. The roots are above ground level, surrounded by cold air on every side, so a hard frost can freeze the whole rootball.

• Bring tender plants in. Chillies, pelargoniums, fuchsias, citrus and other tender pot plants need a frost-free place: a porch, conservatory, cool spare room or heated greenhouse.
• Huddle the rest. Group hardy pots together against a house wall, where they shelter each other and catch a little of the building's warmth.
• Lift them off the ground. Pot feet, or a couple of bits of wood, let water drain away. A pot standing in a saucer of water that freezes is in trouble.
• Mediterranean herbs. Rosemary, thyme and sage mind winter wet more than cold. Overwintering Mediterranean herbs explains why, and suggests moving tender pots under cover between late October and mid-November.

There's more on wrapping pots and which containers crack in frost in protecting pots and containers from frost.

6. Get the greenhouse ready

An unheated greenhouse is not frost-free: on a hard night the inside can dip below freezing too. Before the cold arrives:

1. Clear out spent summer crops and wash the glass, so the low winter light can get in.
2. Put up bubble insulation while the glass is dry and the days are mild. It slows heat loss at night.
3. Hang a max/min thermometer at plant height. A week of readings tells you how cold your greenhouse really gets, before you spend anything on heating.
4. Decide whether you need heat at all. Hardy winter salads cope in an unheated greenhouse with fleece on the coldest nights. Heat earns its keep only if you're keeping tender plants alive until spring.

Heating a greenhouse in winter covers all four, and the greenhouse heater cost calculator works out what a heater would cost to run at today's electricity price.

7. Plant garlic and tidy up

Not every job before the frost is defensive. Autumn, October or November, is the best time to plant garlic in most UK gardens, because it needs a cold spell to split into a proper bulb of cloves. Planting garlic in autumn or spring explains why.

While you're out there:

• Stop feeding anything you're overwintering. Feed now pushes out soft growth that frost blackens first.
• Drain and store hoses and outdoor taps you won't use, so they don't split when water freezes inside them.
• Note what got caught last year. If a frost took you by surprise, put a reminder in your calendar a fortnight before your typical first-frost window. The frost date checker can add the date to your phone's calendar.

The checklist in short

• Look up your typical first-frost window, then watch the forecast for clear, still nights.
• Pick tender crops; ripen green tomatoes indoors.
• Leave hardy crops in the ground; lift and store the rest.
• Lift dahlias once frost blackens the leaves.
• Find fleece, cloches and pegs.
• Bring tender pots in; huddle and lift the rest.
• Clean, insulate and fit a thermometer in the greenhouse.
• Plant garlic, stop feeding, drain the hose.

Do that, and the first frost becomes a night you hear about on the forecast, not one that costs you a crop.