How do I protect plants from frost?

Frost damages plants by freezing the water inside their cells. Protection works by trapping a small amount of ground warmth or by keeping the plant dry, since waterlogged roots freeze more readily and rot afterwards.

What you'll need

• Horticultural fleece
• Pot feet (optional)
• Mulch (optional)
• Cloches (optional)

Step by step

1. Know which plants are actually at risk.Check hardiness ratings. Many plants labelled tender survive with a mulch over the crown, while some apparently hardy plants suffer in wet cold.
2. Cover before the frost arrives, not after.Fleece traps warmth radiating from the ground. Applied after the plant has frozen it does nothing.
3. Use horticultural fleece rather than plastic.Fleece breathes; plastic traps condensation which freezes against the plant and makes the damage worse.
4. Keep the covering off the foliage.Where fleece touches leaves, the cold transfers through. Support it on canes or hoops with a gap.
5. Move pots against a wall and off the ground.Pots freeze from all sides, unlike plants in the ground. A sheltered wall and pot feet make a substantial difference, and grouping them helps.
6. Mulch over the crowns of borderline-hardy perennials.A thick layer of bark, straw or leaves protects the growing point even if the top growth dies back.
7. Keep plants on the dry side over winter.Wet plus cold kills far more plants than cold alone. Improve drainage and avoid watering pots much through winter.
8. Do not cut back frost-damaged growth immediately.Damaged foliage protects the growth beneath it from further frost. Wait until the risk has passed, then cut back to healthy growth.

Tips

• Frost pockets form where cold air collects — at the bottom of a slope or against a solid barrier. The same garden can vary by several degrees.
• A late frost after growth has started does more damage than a hard frost in midwinter, because the new growth is soft and unprotected.
• Fleece can be left on for several days during a cold spell, but remove it when milder weather returns so plants get light and air.

Common mistakes

• Using plastic sheeting to cover plants — It traps condensation, which freezes against the foliage and causes worse damage than no cover at all.
• Covering plants after the frost — Fleece works by trapping ground warmth before the temperature drops. Applied afterwards it achieves nothing.
• Cutting off frost-damaged growth immediately — The damaged material insulates what is beneath it. Wait until the frost risk has passed before cutting back.

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