Frost protection for plants: free fixes first, then fleece and cloches

To protect plants from frost, cover anything tender before nightfall whenever the forecast shows 4°C or below with clear skies and light wind. You do not need to buy anything to start: an old net curtain, an upturned cardboard box or a cut-down plastic bottle over a single plant all trap enough air to take the edge off a light frost. For repeated use through autumn and winter, horticultural fleece and cloches do the same job better and last for years. The other half of frost protection is timing, and that starts with knowing your area's first frost date.

Free frost protection you already own

Before you spend a penny, raid the house. Frost protection is about trapping a layer of still air around the plant overnight, and plenty of household items do exactly that.

Old net curtains

A net curtain draped over plants works much like horticultural fleece: it lets light and moisture through while holding a layer of air around the leaves. Peg the edges down with stones or bricks so it cannot blow off, and take it off mid-morning so the plants get full light and airflow. Charity shops sell them for pennies if yours are long gone.

Upturned cardboard boxes and buckets

For a single tender plant, an upturned cardboard box, bucket or flower pot placed over it in the late afternoon holds the day's warmth around the plant overnight. Remove it in the morning, every morning. A box left on for days will starve the plant of light. Cardboard also collapses when wet, so this is a dry-night fix rather than a season-long one.

Cut-down plastic bottles

A 2-litre drinks bottle with the bottom cut off is a free cloche for a seedling or a young plant. Push it into the soil so it cannot blow away, and leave the cap off for ventilation. This is the same trick Victorian gardeners paid good money for in glass.

Move and huddle your pots

Container plants feel the cold before anything in the ground, because their roots have no surrounding soil to insulate them. Move pots against a south-facing or west-facing house wall, which releases stored daytime warmth overnight, and cluster them together so they shelter each other. It costs nothing and it is often the single most effective move on this page.

Cheap kit worth buying once

Horticultural fleece

Fleece is the workhorse. A single layer of 30gsm horticultural fleece gives around 2°C of protection, according to the RHS, and unlike a box or bucket it can stay on for a few days at a stretch because light and rain pass through it and air can still circulate. Drape it loosely rather than wrapping it tight, weigh the edges down, and use a double layer when the forecast turns properly cold. A roll lasts for years if you dry it before storing it.

Cloches

A cloche is a mini greenhouse for one plant. A bell cloche over a young courgette or a newly planted tomato traps daytime warmth and releases it slowly through the night. The one rule: ventilate on sunny days, because the temperature inside climbs fast even in spring sunshine. The cut-down bottle above is the free version; the glass or rigid plastic version simply lasts longer and holds heat better.

Cold frames

A cold frame is a bottomless box with a clear lid, and it earns its keep twice a year: hardening off seedlings in spring and sheltering pots of not-quite-hardy plants through winter. You can build one from old bricks and a salvaged window for nothing, which is how most allotment cold frames start life.

The fleece and cloche links above are affiliate links to Gardening Naturally, a UK organic gardening supplier. If you buy through them we earn a small commission at no extra cost to you.

What to protect, at what stage

Not everything in the garden needs saving. Match the effort to the plant.

The RHS notes that plants need a spell of cold weather to build frost resistance, so a sudden early frost can catch even hardy plants that have not yet acclimatised. That is why the first frost of autumn and the last frost of spring do more damage than the depths of January. For the detail on which temperatures damage which plants, see our guide to what temperature kills plants.

The two count-back windows before your first frost

Autumn frost protection is not one job on one night. It is two windows of work, counted backwards from your area's typical first frost date. Look up your date by postcode, then put these two windows in the diary.

Three weeks before: the salvage window

• Cut your basil. Basil sulks in cold nights long before frost arrives. Cut it and make pesto rather than losing it to the first cold snap.
• Lift dahlias and other tender perennials. The RHS advises lifting tender perennials such as dahlias and cannas before the first frosts. Doing it in this window means you work in decent weather, not in a panic the night a frost is forecast.
• Harvest green tomatoes to ripen indoors on a windowsill.

One week before: the shelter window

• Bring pots of pelargoniums and fuchsias under cover. A cold greenhouse, a porch or a bright shed is enough. They do not need warmth, just protection from freezing.
• Stage your kit. Fleece, pegs, cloches: by the back door, not buried in the shed. When the forecast turns, you have minutes of work, not an evening of hunting.

On the night: a simple routine

1. Check the overnight forecast in the afternoon. The Met Office says frost may be possible when 0°C to 4°C is forecast with little or no cloud and light winds.
2. Cover tender plants in the late afternoon, while some daytime warmth is still in the soil.
3. Peg or weigh everything down. A cover that blows off at 2am protected nothing.
4. Uncover mid-morning once the air has warmed, so plants get light and air.

For a postcode-level view on borderline nights, our Garden Weather Forecast shows an Estimated Frost Risk Tonight built from live Met Office forecast data.

Frequently Asked Questions

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