UK pruning guide · RHS timing
When to prune costmary in the UK
Why the timing differs here
For shrubs that flower on the current season's growth, the RHS times pruning to early or mid spring — after severe weather has passed and once the growth buds begin to swell. In Britain that is usually March into April rather than the February common in warmer regions; prune too early and the new shoots meet a late frost.
How to prune costmary
Deadhead spent flower stems by cutting to the base. In late autumn or early spring, cut all stems down to just above soil level. Divide congested clumps every 3–4 years to maintain vigour.
Costmary is a vigorous perennial herb that spreads by rhizome more than it needs pruning. Cut back flowered stems after blooming in late summer to encourage fresh basal foliage. Cut the whole plant down to ground level in autumn or early spring to clear old growth and stimulate new aromatic leaves.
More costmary care for British gardens
Care at a glance
Pruning costmary in the UK — FAQ
When should I prune costmary in the UK?
Prune costmary in early to mid spring. For shrubs that flower on the current season's growth, the RHS times pruning to early or mid spring — after severe weather has passed and once the growth buds begin to swell. In Britain that is usually March into April rather than the February common in warmer regions; prune too early and the new shoots meet a late frost.
Is it illegal to prune costmary in spring or summer in the UK?
There is no nesting-bird restriction that realistically applies to costmary, since birds do not nest in it. The Wildlife and Countryside Act 1981 still protects any active nest you do find anywhere in the garden — the rule is about the nest, not the plant.
How do you prune costmary?
Deadhead spent flower stems by cutting to the base. In late autumn or early spring, cut all stems down to just above soil level. Divide congested clumps every 3–4 years to maintain vigour.
How often does costmary need pruning in a British garden?
Once or twice a year. Costmary is a vigorous perennial herb that spreads by rhizome more than it needs pruning. Cut back flowered stems after blooming in late summer to encourage fresh basal foliage. Cut the whole plant down to ground level in autumn or early spring to clear old growth and stimulate new aromatic leaves.
Why is UK pruning timing different from American advice?
Most pruning guides online are written for US conditions and anchored to USDA zones. Britain's maritime climate gives milder winters but later, less predictable last frosts — from March in the south-west to mid-May in the north — so the RHS advises against winter pruning for most plants: it pushes out soft growth that a late frost then kills. Britain also has the nesting-bird law, which has no US equivalent.