A hydrangea can be healthy, leafy and almost flowerless after the wrong pruning. That's because 'hydrangea' covers several plants with different habits. Many familiar mophead and lacecap types flower largely from buds associated with older stems, while panicle and smooth hydrangeas respond well to pruning a framework in spring.
Before you pick up the secateurs, identify which hydrangea is in front of you. The pruning method follows the plant, not the size of the faded brown flowerheads or how untidy the shrub looks in January.
Find out which hydrangea you have
Mophead hydrangeas have full, rounded clusters of flowers. Lacecaps usually have smaller fertile flowers in the centre with a ring of larger showy flowers outside. Both commonly belong to Hydrangea macrophylla, and H. serrata has broadly similar pruning needs.
Hydrangea paniculata has cone-shaped flowerheads, often opening pale and changing colour as the season progresses. Hydrangea arborescens includes the familiar large rounded white flowerheads of cultivars such as 'Annabelle'. They flower on growth produced in the current season and are pruned differently.
Climbing hydrangea, H. anomala subsp. petiolaris, is a wall-covering climber rather than a free-standing bush. Oakleaf hydrangea, H. quercifolia, also has its own shape and generally needs relatively little pruning. If unsure, compare the leaves and flowers with a reliable plant identification guide before making substantial cuts.
When should you prune?
For most mophead and lacecap hydrangeas in the UK, late winter to spring is the usual time for annual tidying. Leaving faded mophead blooms on over winter can provide some protection to the buds beneath them from frost.
In a cold garden, waiting until the most severe frosts are past may be sensible. A warm weekend in January does not mean winter is over.
Panicle and smooth hydrangeas can be pruned during late winter or early spring before vigorous new growth. Climbing hydrangeas are normally trimmed immediately after flowering in summer. Timing matters as much as the cut itself.
How to prune mophead hydrangeas
Begin by examining the faded flowerhead and the stem beneath it. Look for a strong, healthy pair of buds below the flower. Cut the old flowerhead away just above that pair, leaving those buds to develop.
Repeat carefully rather than cutting the whole shrub to a uniform height. A mophead can flower well without severe annual pruning. The goal is to preserve healthy stems that carry potential flowers while improving shape.
On an established shrub, you can remove one or two of the oldest, tired stems at the base to encourage fresh replacement growth. Avoid removing a large proportion of the old structure each year unless you're deliberately renovating a plant and accept losing flowers.
Lacecaps need a similarly light touch
Lacecap hydrangeas are often hardier than mopheads. Some gardeners remove spent flowerheads after flowering, cutting to a suitable pair of leaves below. Alternatively, waiting until spring is often practical when you're uncertain of the forecast.
Remove dead, damaged and crossing stems, then stop. A lacecap that has a natural loose habit may look worse if every stem is shortened to the same line.
If several stems lean over a path, reduce those particular shoots appropriately, understanding that removing their tips may sacrifice some flowering. A selective cut is usually preferable to a complete haircut.
Pruning panicle and smooth hydrangeas
Hydrangea paniculata and H. arborescens produce flowers on new shoots made during the growing season. RHS guidance therefore permits annual spring pruning back to a permanent framework of branches.
Remove weak and dead stems first, then shorten the previous year's shoots to pairs of healthy buds on that framework. Harder pruning can encourage strong upright growth and larger flowerheads, but may produce fewer, heavier heads than gentler pruning.
An established shrub can be maintained at a taller framework if you want height. Don't copy a neighbour's 25cm stump cut without checking the species and the effect you're trying to achieve.
What to do with a climbing hydrangea
Climbing hydrangeas attach themselves to walls and supports as they grow. They generally need only selective trimming to stop shoots spreading across windows, gutters or roof tiles.
Prune over-long shoots after flowering in summer. Leave as much healthy flowering wood as practical, because drastic pruning can remove much of the plant's display for following years.
A very overgrown climber may be renovated over several seasons rather than cut hard in one go. Check for birds' nests before pruning and avoid damaging any active nest. If the plant is high above safe ladder height, use a qualified gardener instead of stretching from an unstable position.
How to remove dead or frost-damaged wood
Dead stems tend to be brittle and may show no green tissue beneath the bark. Work back to healthy living wood, making a clean cut just above an appropriate bud or side shoot.
Late frost can blacken emerging growth on hydrangeas. Wait until the extent of damage is clear, then prune affected tips back to a sound pair of buds. New leaves may appear lower down the stem.
Use clean sharp secateurs and disinfect them when dealing with suspected disease. Pulling at brittle stems by hand can tear bark and damage buds you meant to keep.
Renovating a badly overgrown hydrangea
An old mophead may develop a congested centre with a jumble of woody stems. Removing one or two old stems annually is a measured way to bring in new growth while keeping much of the flowering display.
You can cut a very neglected mophead hard to the base, but that typically costs you flowers in the following summer. Decide whether a one-year setback is acceptable before starting.
For panicle hydrangeas, an existing framework can often be rebuilt with selected cuts, provided healthy buds and appropriate branches remain. A shrub with serious dieback or root problems needs diagnosis as well as pruning.
Why a hydrangea has stopped flowering
The most common pruning mistake is cutting a mophead hard every spring. You may repeatedly remove the shoots that would have flowered. Give it time to rebuild and use only light pruning next year.
Late frost, too much shade or severe drought can also affect flowering. A plant producing plenty of leaves isn't proof that it has received appropriate light and moisture.
If someone else planted the shrub and you don't know its name, observe it for a season. The shape of the flowerhead and timing of bloom will usually tell you far more than its winter outline.
Care after pruning
Remove trimmings from the bed, especially if any show disease. Apply a suitable mulch of organic matter on moist, weed-free soil, keeping it away from the stems.
Hydrangeas need regular moisture during dry spells. A drought-stressed plant may struggle to support new shoots, especially if it grows against a wall or beneath trees.
Don't chase every cut with extra feed. The best results come from identifying the plant, pruning the right stems at the right time and giving the roots conditions that allow healthy regrowth.