When to prune hydrangeas, and the other shrubs in a border

Which hydrangea is it?

Hydrangeas fall into a handful of groups, and each is pruned differently because each flowers on different wood. Mopheads and lacecaps form next year's flower buds at the top of this year's stems, so cutting those stems short removes the flowers. Paniculata and arborescens flower on shoots that grow from scratch each spring, so they take hard pruning in their stride.

• Mophead and lacecap (Hydrangea macrophylla): big rounded heads, or flat heads ringed with larger florets, in blue, pink or white.
• Mountain hydrangea (H. serrata): a smaller, neater lacecap.
• Paniculata: cone shaped flowerheads, usually white ageing to pink, on a large upright shrub.
• Smooth hydrangea (H. arborescens), including the variety Annabelle: very large, round white or green heads on thin stems.
• Climbing hydrangea (H. anomala subsp. petiolaris): self clinging on walls and fences, with flat white flowers.
• Oakleaf and rough leaved (H. quercifolia and H. aspera): distinctive leaves, minimal pruning.

The timing at a glance

These are the Royal Horticultural Society's timings. None of the groups is pruned in autumn, because an autumn cut removes next summer's flower buds on mopheads and lacecaps.

Mopheads and lacecaps: leave the heads on all winter

The faded flowerheads look untidy by November, and the temptation is to cut them off with the autumn tidy. They are better left. The dry heads shelter the plump buds just beneath them from frost, and those buds are next summer's flowers.

Once the hardest frosts are over in early spring, each old head is followed down the stem to the first strong, healthy pair of buds and cut just above it. On a mature plant, one or two of the oldest, thickest stems also come out at ground level, which makes room for young growth and keeps the shrub from becoming a mass of tired wood. A mophead that has been cut back hard all over will usually grow vigorously and then fail to flower that year.

Paniculata and Annabelle: hard pruning is fine

Because these flower on new growth, they can be cut back each spring to a low framework of older wood, to a pair of buds on each stem. The RHS gives about 25cm as the lowest height for hard pruning, or around 60cm for a larger shrub. Harder pruning gives fewer but bigger flowerheads; lighter pruning gives more, smaller ones on a taller plant.

Annabelle's thin stems can flop under the weight of large heads after rain, and leaving a slightly taller framework gives the new stems more support.

Climbing hydrangea: after flowering, and sparingly

Climbing hydrangea flowers in early summer and is pruned immediately afterwards, cutting back only the shoots that have grown out from the wall or are heading for gutters, windows and roof tiles. The RHS advice is to leave as much of it unpruned as possible. A climber that has badly outgrown its space is reduced over three or four years, a section at a time, because cutting it all back at once can stop it flowering for several seasons.

The same rule for the rest of the border

Hydrangeas follow a principle that applies to most flowering shrubs: work out when it flowers and whether those flowers come on old wood or new.

• Deciduous shrubs that flower between November and June, such as forsythia, weigela, philadelphus and flowering currant, are pruned straight after flowering, cutting the flowered stems back to strong young shoots.
• Shrubs that flower from July to October on new growth, such as Buddleja davidii, caryopteris and perovskia, are cut back in early to mid spring to within a bud or two of the woody framework.
• Most evergreens are pruned in mid-spring once frost has passed; early flowering ones like camellia and rhododendron wait until they finish flowering.
• Lavender is trimmed after flowering to within 1.5 to 2.5cm of the previous year's growth, never into bare old wood.
• A badly overgrown deciduous shrub is renovated over three years, removing a third of the oldest stems each year.

Herbaceous perennials can be cut back any time from autumn to spring. Leaving the dead stems standing until March gives seed heads, shelter for insects and winter structure; cutting in autumn looks tidier.

Getting it done

Shrub pruning is part of a gardener's seasonal round and is charged by time, at £25 to £45 an hour across most of the UK. Asking a gardener when they would prune each shrub in the border, and why then, gives a clear plan for the year, with mophead and lacecap hydrangeas left uncut until spring so they keep next summer's flowers.