How to protect plants from frost (UK)

By Sophie Sparkes · October 2026 · 7 min read

The first frost of the year rarely gets much warning. One clear, still night in October or November and tender plants that looked fine at dusk are black by breakfast. Most of that damage is preventable with a few simple jobs, done on the right evening.

Short answer: on any clear, still night with a forecast low of 3°C or below, cover tender plants with horticultural fleece, move pots against the house wall or into a shed or greenhouse, and raise containers on pot feet. Mulch the crowns of borderline-hardy perennials, wrap pots that cannot be moved, and do not cut back tender plants in autumn, because the old growth protects the crown. Take fleece off in the day when it is mild so plants get light and air.

When to expect frost in the UK

Most of the UK sees its first frost between mid-October and mid-November. Rural, inland and northern gardens usually get it first, sometimes in late September; city centres and coastal gardens in the south and west can stay frost-free into December. Your own garden can also differ from the forecast: cold air sinks, so the bottom of a slope or a hollow is a frost pocket that freezes when the top of the garden does not.

Signs a frost is coming tonight

• Clear skies after dark. Cloud acts like a blanket; without it, heat escapes fast.
• Little or no wind. Still air lets the cold settle.
• A cold, dry day after a spell of northerly or easterly wind.
• A forecast low of 3°C or below. Treat that as a frost night.

Which plants need protecting?

• Tender plants that cannot take any frost: pelargoniums (bedding geraniums), tender fuchsias, cannas, dahlias, begonias, citrus, most succulents and tender salvias.
• Anything in a pot. Roots in a pot are far more exposed than roots in the ground, so even hardy plants can be killed when the compost freezes solid.
• Borderline-hardy perennials such as agapanthus, penstemons, some salvias, and tree ferns and bananas.
• New plantings that have not rooted in yet, and early blossom on fruit trees in spring.

How to protect plants from frost

1. Cover them with horticultural fleece. A single layer of standard fleece keeps a plant a couple of degrees warmer, which is often the difference between survival and loss. Use two layers, or a thicker 30gsm winter fleece, in a cold spell. Drape it right to the ground and weigh down the edges, because the warmth comes up from the soil.
2. Move pots somewhere sheltered. Group them together against a house wall, under the eaves, or into a shed, garage, porch or greenhouse. A south or west-facing wall is warmest.
3. Raise pots on pot feet so they drain freely. Wet compost freezes harder and cracks terracotta.
4. Wrap pots you cannot move in bubble wrap or hessian to insulate the roots.
5. Mulch the crowns of borderline perennials with a thick layer of bark, compost, straw or leaves.
6. Leave the old growth on. Do not cut back tender perennials such as penstemons or salvias in autumn. The top growth shelters the crown; tidy them in spring.
7. Water in the morning, not the evening, so the compost is not cold and wet as the temperature drops.

What not to use

Plastic sheeting touching the leaves makes things worse: plastic conducts cold, so leaves freeze where they touch it, and it traps condensation. If you only have plastic, hold it off the plant with canes or use it to make a cloche. Avoid feeding with nitrogen in late summer and autumn too, because soft new growth is the first to be damaged.

Protecting a greenhouse

Line an unheated greenhouse with bubble wrap to keep it a few degrees warmer. A small electric or paraffin heater set to come on at about 5°C keeps it frost-free for overwintering tender plants. Use a max-min thermometer so you know how cold it actually gets at night, and ventilate on mild days to stop damp and grey mould.

Is my plant frost damaged? What to do next

Frost-damaged leaves look dark, glassy or water-soaked at first, then turn black or brown and limp. Do not cut the damage off straight away. The dead growth protects the healthy buds beneath it from the next frost. Wait until spring, when you can see where new growth starts, then cut back to just above it. Many plants that look dead in January reshoot from the base in April.

Frost protection questions

At what temperature should I cover my plants?

When the forecast low is 3°C or below on a clear, still night. Forecasts measure air temperature above the ground, and the ground and low plants can be several degrees colder, so waiting for a forecast of 0°C is often too late.

Does fleece really protect plants from frost?

Yes. A single layer of horticultural fleece typically keeps plants a couple of degrees warmer, and two layers more. It works best draped to the ground, because it traps the warmth rising from the soil. It also lets light and air through, so it can stay on for a few days in a cold spell.

Can I use a bedsheet to protect plants from frost?

For a night or two, yes. An old sheet, blanket or cardboard box works in an emergency. Take it off in the morning, and do not let it get soaked, because wet fabric gets heavy and cold. Avoid plastic touching the leaves.

Should I water plants before a frost?

Water in the morning if the soil is dry, not in the evening. Moist soil holds a little more warmth than dust-dry soil, but cold, wet compost in pots overnight freezes harder, so give plants the day to drain.

Will frost kill my potted plants?

It can, even hardy ones, because compost in a pot freezes much faster and deeper than soil in a border. Move pots together against a wall or under cover, raise them on pot feet, and wrap the pot itself in bubble wrap or hessian.

When is it safe to stop protecting plants?

Usually after the last frost in spring, which is mid-May in much of southern England and late May to early June further north and in cold inland gardens. Late frosts in May are common, so keep fleece handy until then.