Why is my rosemary dying?

Why rosemary dies of wet feet rather than cold, the beetle that strips it, and the drainage and pruning that keep a plant going for years.

Difficulty: beginner
Time: 20 min
Read: 3 min

Short answer

Rosemary is killed by wet, not by cold. Waterlogged winter compost rots the roots and the plant goes grey and brittle in spring. Grow it in gritty free-draining compost, raise pots on feet, never let it stand in a saucer, and check for rosemary beetle.

Everything rosemary needs comes from where it grows wild: poor, stony, sharply drained ground in full sun with dry summers. The commonest UK gardening instincts — rich compost, regular watering, a saucer under the pot — are all wrong for it.

Step by step

Check the drainage first.Lift the pot. Heavy and wet days after watering means waterlogging, which is the leading cause of rosemary death. Compost should be moist, never sodden.
Repot into a gritty mix.Loam-based compost with a third added horticultural grit or sharp sand. Ordinary multipurpose compost holds far too much water for rosemary through a UK winter.
Raise pots off the ground.Pot feet, and no saucer from October to April. A pot standing on a flat surface effectively seals its drainage hole.
Move winter pots under shelter.Against a house wall or under an overhang, where it gets light but not the worst of the winter rain. This alone saves most rosemary plants.
Look for rosemary beetle.Metallic green and purple striped beetles about 8mm long, with grey grubs, feeding on the foliage. Pick them off, or shake the plant over a sheet of paper.
Check for grey mould in the centre.A congested, unpruned plant holds damp air inside it. Thin it and remove dead material to get air through.
Prune lightly after flowering.Trim by about a third after the spring flowers, cutting only into growth that still has leaves. Rosemary will not reshoot reliably from bare wood.
Do not feed it.Rich feeding produces soft growth that rots in winter and is more attractive to pests. Rosemary wants poor soil.
Plant in the ground on a slope or a raised bed.In heavy soil, plant on a mound or in a raised gravelly bed. Sharp drainage matters more than the position.
Take cuttings as insurance.Semi-ripe cuttings in late summer root easily. Given how often rosemary is lost in a wet winter, having a spare plant is sensible.

Tips

Rosemary dies of wet, not cold. It is hardy to well below freezing in dry soil.
No saucer under the pot from October onwards.
It does not reshoot reliably from bare wood, so prune lightly and often rather than hard and rarely.

Common mistakes

Standing a rosemary pot in a saucer through winter — The compost stays saturated for months, the roots rot, and the plant goes grey and brittle in spring while everyone blames the frost.
Cutting an old woody rosemary back hard to rejuvenate it — Like lavender, it does not reliably produce new shoots from bare wood. A hard cut usually kills the stem it was made on.

If it doesn't work

Grey, brittle, dry-looking foliage in spring

Cause: Root death over winter from waterlogging — Fix: Check the roots. Brown soft roots mean it is finished. Repot survivors into gritty compost and shelter from winter rain.

Foliage stripped, metallic striped beetles present

Cause: Rosemary beetle — Fix: Pick off adults and grubs, or shake the plant over paper. It also attacks lavender, sage and thyme.

Woody and bare at the base

Cause: Never pruned, or pruned too hard — Fix: Trim lightly into green growth after flowering each year. Replace a plant that is bare throughout.

Dying from the centre outward

Cause: Damp still air in a congested plant — Fix: Thin the plant, remove dead material and improve air movement.

Questions people ask

Is rosemary hardy in the UK?

Yes, in dry, sharply drained soil — it survives hard frosts easily. What kills it is a wet winter, not a cold one.

Can I cut rosemary back hard?

No. It does not reliably reshoot from bare wood. Trim by about a third after flowering, cutting only into growth that still carries leaves.

What is eating my rosemary?

Almost certainly rosemary beetle — metallic green and purple stripes, about 8mm long. It also attacks lavender, sage and thyme, and hand picking is the practical control.