How to Protect Plants from Frost: A Simple UK Guide

By Ann, gardener and garden designer at Ann's Garden Heaven

The first proper frost always seems to arrive on the one night you forgot to check the forecast. One clear, still night is all it takes to turn a pot of salvias into black mush. The good news? Protecting your plants takes about ten minutes once you know what to do – and most of it costs very little.

Here's how I keep my garden safe through a British winter.

How to tell a frost is coming

• Clear skies and no wind. Cloud acts like a blanket. On a clear, calm night, heat escapes from the ground quickly and frost forms.
• A cold, bright afternoon. If it's under 5°C by teatime and the sky is clearing, assume a frost.
• Check the forecast for your garden. Our Garden Weather page shows tonight's lowest temperature for your town or postcode and warns you when it drops near freezing.

In most of the UK the first frosts arrive between October and November, and the last ones can linger until May – later in the north and in low-lying "frost pockets".

Which plants need protecting?

• Tender plants: pelargoniums (geraniums), fuchsias, salvias, dahlias, cannas, citrus and most patio plants bought in summer.
• Borderline plants: agapanthus, tree ferns, bananas, olive trees in pots, cordylines and young plants not yet established.
• Anything in a pot. Roots in containers are far more exposed than roots in the ground – a hard frost can freeze the whole rootball.
• New growth and blossom in spring, especially on fruit trees, potatoes and early-sown seedlings.

Step-by-step: protecting your plants tonight

Step 1: Move what you can

Bring the most tender pots into a greenhouse, porch, shed or cool spare room. If they have to stay outside, group them together against a house wall – walls give off stored heat overnight, and plants huddled together shelter each other.

Step 2: Lift pots off the ground

Stand pots on pot feet or a couple of bricks. This stops them sitting in freezing water and helps prevent terracotta from cracking.

Step 3: Cover with horticultural fleece

Fleece is the gardener's best friend in winter. It lets light, air and water through but traps a few precious degrees of warmth – enough to save most plants from a light frost.

• Drape it loosely over plants or use a ready-made fleece jacket with a drawstring.
• Peg or weigh down the edges so the wind can't whip it away.
• For hard frosts, use two layers.
• Avoid plastic sheeting directly on leaves – it conducts cold and causes condensation that freezes.

Step 4: Wrap the pots, not just the plants

Wrap containers in hessian, bubble wrap or old blankets to stop the roots freezing. Leave the drainage holes clear.

Step 5: Mulch around tender roots

For plants in the ground – dahlias you're leaving in, agapanthus, penstemons – pile a thick layer (8–10cm) of bark, straw or compost over the crown. It works like a duvet for the roots.

Step 6: Use cloches for veg and seedlings

Bell cloches, tunnels and mini greenhouses protect winter salads, young broad beans and spring seedlings. Open the ends on mild days so they don't overheat or get mouldy.

What NOT to do

• Don't water in the evening before a frost – wet compost freezes harder. Water in the morning if needed.
• Don't cut back frost-damaged growth straight away. The blackened leaves protect the buds underneath. Wait until spring when new growth appears.
• Don't feed plants late in the year. Fertiliser encourages soft new growth that frost kills easily.
• Don't forget to uncover. Remove fleece on mild, sunny days so plants get light and air.

Help! My plant got frosted

Don't panic. Move it somewhere sheltered and out of morning sun – thawing slowly does less damage than thawing fast. Leave the damaged leaves on, keep the compost just moist, and wait. Many plants, especially those with woody stems or bulbs, will reshoot from the base in spring.

Your frost protection checklist

• Horticultural fleece or fleece jackets
• Pegs or bricks to hold covers down
• Pot feet
• Bubble wrap or hessian for pots
• Bark or straw mulch
• Cloches or a mini greenhouse

Shop this guide

• Winter Protection – fleece, jackets, cloches and covers
• Check tonight's frost forecast for your garden

A little preparation now means a garden full of healthy plants come spring. Keep an eye on the sky, keep the fleece handy, and your plants will thank you.

– Ann

Photos from Wikimedia Commons, shared under Creative Commons and similar free licences. Follow each link for the photographer and licence.