How to prune a flowering shrub

When

Best: Mar–Jun (northern hemisphere — southern hemisphere: add six months)

Late winter for new-wood bloomers, right after the flowers fade for old-wood ones. Dead, damaged or diseased wood can come off in any month.

Never

✗ Never prune an old-wood shrub in late summer, autumn or winter — next year's flower buds are already set.
✗ Never prune non-reblooming bigleaf or lacecap hydrangea after about 1 August.
✗ Never shear a flowering shrub into a ball — it destroys both the form and the flowering wood.
✗ Never leave a stub, and never cut flush with the trunk.
✗ Never top a shrub or tree back to stubs to reduce its height.

Months in these rules are northern-hemisphere — in the southern hemisphere, shift them by six.

• Find out first whether it blooms on old wood or new — that single fact decides the whole schedule.
• Spring bloomers (lilac, forsythia, weigela, azalea) bloom on old wood: prune within 2-3 weeks of the flowers fading.
• Summer bloomers (butterfly bush, panicle hydrangea, summer spirea) bloom on new wood: cut them back in late winter.
• Renew lilac and forsythia by taking about a third of the oldest stems to the ground.
• Non-reblooming bigleaf hydrangea: prune only just after bloom, and stop by about 1 August.
• Reblooming hydrangeas (Endless Summer and similar) flower on old and new wood, so timing matters far less.
• Deadhead by cutting just above the next healthy pair of leaves or buds.
• Take dead, diseased or damaged wood out first, in any month — that comes before every season rule here.
• Cut just outside the branch collar; on limbs over 1.5 in (4 cm) use three cuts so the bark can't tear.
• Take no more than about a quarter of a shrub in one go.

Sourced from US university cooperative-extension services and the RHS, then adversarially fact-checked — every rule carries its source.

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