When to cut back hydrangeas in the UK: mopheads, paniculatas and climbers

Every autumn the same question comes up in gardens across the UK: the hydrangea has finished, the flowerheads have gone brown and papery, and it looks as though it needs tidying. Whether you should reach for the secateurs depends entirely on which hydrangea you have, because the common types flower on different wood and respond very differently to the same cut. Prune a mophead in October and you may remove next summer's flowers; leave a paniculata unpruned for years and it turns into a tangle of weak stems with small heads.

First, identify the type

The three groups most often grown in British gardens behave in distinct ways, and a quick look at the plant will usually tell you which one you have.

Mopheads and lacecaps: leave the heads on, cut in spring

Hydrangea macrophylla sets its flower buds in late summer and carries them through winter near the tips of last year's stems. Those buds are vulnerable to frost, and the dead flowerheads above them act as a small umbrella. That is why the standard advice in the UK is to leave the spent heads in place all winter, however untidy they look, and remove them only when the worst frosts are over. In most of England that means the second half of March; in the north of England and Scotland, early April is safer.

When you do prune, cut each old flowerhead back to the first strong pair of fat buds below it, which is usually only a few centimetres. On plants that are more than three or four years old, also remove one or two of the oldest, thickest stems right down to the base, which lets light into the centre and encourages fresh shoots. Never cut all the stems to the ground: the plant will survive, but you will lose a full year of flowers.

If a hard frost does catch the plant after you have pruned, you may see blackened shoot tips in April. Trim those back to healthy growth and accept that flowering will be reduced that year.

Paniculata and 'Annabelle': prune hard in late winter

These two are the forgiving ones. Because they flower on growth made in the current year, cutting them back in February or early March, before the buds break, removes nothing you will miss. The harder you cut, the fewer but larger the flowerheads; a lighter prune gives more heads on a bigger plant.

For Hydrangea paniculata, the usual approach is to build a permanent framework of stems 30 to 60 cm tall and cut last year's growth back to one or two pairs of buds above it each year. For 'Annabelle', many gardeners cut to around 30 cm from the ground, which keeps the plant compact; cutting it very low produces thinner stems that collapse under the weight of the enormous heads in summer, so slightly higher is often better.

Climbing hydrangea: after flowering, if at all

Climbing hydrangea needs little pruning once established. If it is outgrowing its wall or fence, shorten the outward-growing shoots and any that have strayed beyond their space straight after flowering, in July. Pruning in late winter removes the flower buds. Older plants that have become bare at the base can be renovated gradually over two or three years rather than in one go.

What about the autumn tidy-up?

The temptation to cut everything back in October is strong, and for the new-wood types it does no harm, though it also offers no benefit over waiting until February. For mopheads and lacecaps it is the one job to avoid. Resist deadheading them in autumn; you can remove the brown heads in spring in a few minutes. The one exception is a plant growing in a very sheltered, mild spot, where some gardeners deadhead in autumn without losing flowers, but that is a gamble with the weather.

Many professional gardeners in the UK schedule hydrangea pruning as part of a late-March visit alongside rose pruning and the first lawn cut, which is one reason spring visits book up early. If you use a regular gardener, it is worth telling them which type you have, or asking them to check before they cut. If you are looking for someone, our listings of local gardeners cover every major city.

Why hydrangeas sometimes stop flowering

If a mophead has produced leaves but no flowers for a season or two, the likely causes are pruning at the wrong time, a late frost that killed the buds, or too much shade. Plants in heavy shade grow leggy and flower poorly; moving them to a spot with morning sun and afternoon shade usually helps. A hydrangea that has been cut to the ground by an enthusiastic tidy-up will normally flower again the second summer after the cut.

Flower colour is a separate question. Blue flowers on H. macrophylla need acid soil (pH below about 5.5) and available aluminium; on neutral or alkaline soil the same plant flowers pink. White-flowered cultivars stay white regardless. Paniculata heads are not affected by soil pH at all.

Sources: Royal Horticultural Society, pruning guidance for Hydrangea macrophylla, Hydrangea paniculata and Hydrangea arborescens, and RHS advice on hydrangea flower colour and soil pH; Met Office data on average last frost dates across the UK, which vary from early April in the south-west to mid-May in upland and northern areas. Pruning dates in this article are for typical lowland gardens; adjust later in cold or exposed sites.

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