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Cold and frost damage

Frost freezes water inside soft tissue and ruptures the cells. The next morning shoots look glassy or water-soaked, then blacken. Tender crops like basil, tomatoes and squash die outright; hardier plants lose their new growth and blossom.

Light & temperature
Blackened, frost-damaged shoot tips on a young plant
Blackened, frost-damaged shoot tips on a young plant

What it looks like

Frost hits the softest, highest, most exposed growth first.

  • The morning after, leaves look dark and water-soaked.
    Glassy leaves The morning after, leaves look dark and water-soaked.
  • Within a day or two, the tips shrivel and blacken.
    Black shoot tips Within a day or two, the tips shrivel and blacken.
  • Fruit blossom turns brown in the centre and will not set.
    Browned blossom Fruit blossom turns brown in the centre and will not set.
  • Basil and cucumbers show bronzed, spotted leaves after nights under 10 °C (50 °F), even without frost.
    Chilling on warm crops Basil and cucumbers show bronzed, spotted leaves after nights under 10 °C (50 °F), even without frost.

How to confirm it

Match the damage with the weather.

  1. Check the forecast history

    Was there a clear, still night with a ground frost in the last few days?

  2. Look at the pattern

    Exposed tops and outer shoots are hit; sheltered, lower growth is not.

  3. Scratch the stem

    Green beneath the bark means the plant is alive and will regrow.

What to do

Be patient: the extent of damage takes a week to show.

  1. Leave the damage for now

    Dead shoots protect what lies beneath from the next frost. Prune once the risk has passed.

  2. Cut back to live growth

    In late spring, cut blackened shoots back to healthy buds.

  3. Replace tender annuals

    Basil, squash and tomatoes killed at the base will not regrow; resow or replant.

  4. Water and feed lightly

    Once new growth appears, support it with water and a light feed.

Prevent it next time

  • Plant out tender crops only after your last frost date, and harden them off first.
  • Cover plants with a double layer of fleece on frosty nights.
  • Avoid high-nitrogen feed late in the season, which makes soft, frost-prone growth.
  • Keep tender plants out of frost pockets at the bottom of slopes.

What not to do

Do not prune frost-damaged shrubs in winter or early spring; wait until new growth shows where the live wood starts.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Frost damage, Royal Horticultural Society
  2. Fruit: protecting from frost, Royal Horticultural Society