Frost damage

also called Frost burn, Late frost

Soft new growth and open flowers blackened by late frosts. Fleece on cold nights, avoid planting in frost pockets, and resist cutting damage away until frosts pass.

Disorder Serious Doesn't spread

What you'll see

Soft new leaves and shoot tips go limp and water-soaked overnight, then blacken and dry to brown paper.
Only the growth that was exposed is hit — the lower or sheltered side of the same plant is untouched.
Open blossom turns brown at the center; cut a flower in half and the ovary is black instead of green.
Damage appears sharply along one line, the height the cold air settled to, or on the side facing the dawn sun.
Fruit that sets after a frost may carry a corky russet band around the middle.

Why it happens

Not a disease at all. Ice crystals form inside the cells of soft, unhardened tissue and rupture their walls, so the tissue collapses when it thaws. Rapid thawing in early morning sun does as much harm as the freezing itself, which is why east-facing plants suffer most.

Clear, still, cloudless nights in late spring, after a warm spell has drawn plants into soft growth. Cold air runs downhill and pools against walls, hedges and closed gates, so frost pockets are far colder than open ground a few meters away.

Treating it

Leave the damaged growth in place — it shelters the buds beneath and there may yet be another frost.
Cut back to healthy tissue only once all danger of frost has passed, usually late May or early June.
Water and mulch, and give a gentle balanced feed to support the replacement growth.
Shade or gently mist frosted plants before the sun reaches them so they thaw slowly.
Be patient with woody plants; most reshoot from dormant buds even when they look dead.

Keeping it away

Cover vulnerable plants with two layers of horticultural fleece on clear, still nights, removing it by day.
Site tender and early-flowering plants out of frost pockets and away from east-facing walls.
Do not plant out or harden off too early, and keep tender plants under cover until the local last-frost date.
Avoid high-nitrogen feeds late in the season, which push soft growth that cannot harden.
Choose late-flowering cultivars of apples, pears and plums in a cold garden, and leave a gap under hedges so cold air drains away.

Who gets it

Potatoes, beans, courgettes and other tender vegetables, early blossom on fruit trees, magnolias, camellias, hydrangeas and all half-hardy bedding.

and 34 more in the catalog