When and how do I prune a hydrangea?

Nearly every hydrangea that fails to flower has been pruned as though it were the other type. The plant is not fussy about much else, so getting this one decision right is most of what growing them well involves.

What you'll need

• Secateurs
• Loppers for old wood
• Gloves

Step by step

1. Identify the type first.Rounded ball flowers or flat lacecaps on rounded leaves are macrophylla — mophead or lacecap. Cone-shaped panicles on pointed leaves are paniculata. Large white domes on thin stems are arborescens, usually 'Annabelle'. Climbing hydrangea is a fourth case.
2. Leave mophead heads on over winter.The dead flowerheads protect the buds beneath from frost. Cutting them off in autumn is the second most common reason a mophead does not flower.
3. Cut mopheads and lacecaps in early spring.Once the frosts are largely past and the buds are swelling, take each old head off cutting back to the first strong pair of buds below it. That is all most plants need.
4. Thin an old mophead rather than shortening it.Remove one or two of the oldest, thickest stems right down to the base each year. This renews the plant without removing this year's flowers.
5. Cut paniculata hard in late winter.February or March, back to a permanent low framework roughly 300 to 600mm high, leaving a pair of buds above the previous year's cut. Over years this builds a knuckled stubby frame.
6. Cut arborescens hard too, but consider height.'Annabelle' cut to the ground gives enormous heads on stems that flop. Cutting to about 300mm gives slightly smaller heads on stems that stand up.
7. Prune climbing hydrangea after flowering.Hydrangea petiolaris flowers on old wood. Shorten the outward-growing shoots after flowering in summer and leave the framework alone.
8. Renovate a badly overgrown mophead in stages.Cutting the whole plant to the ground gives strong growth and no flowers for two years. Removing a third of the oldest stems each year for three years renews it while keeping some flower.
9. Feed and mulch after pruning.A general fertiliser in spring and a mulch of compost. Hydrangeas are thirsty and hungry, and both jobs are easiest immediately after pruning.

Tips

• Leave the dead heads on a mophead all winter. They are frost protection, not untidiness.
• Cone-shaped flowers on pointed leaves means cut hard. Round flowers on round leaves means barely cut.
• If you genuinely cannot tell which you have, do nothing for a year and watch where the flowers come from.

Common mistakes

• Cutting a mophead hard back in autumn or spring — The flower buds for the coming summer are already formed on last year's wood, near the tips. Cutting them off removes the entire year's flowering.
• Only lightly trimming a paniculata — It gets progressively taller and leggier with smaller flowers each year. These types want a hard annual cut and respond to it with bigger heads.

If it doesn't work

Questions people ask