Photo: Schorle, CC BY-SA 4.0 · source
Pruning guide · Shrub
Mountain hydrangea: when and how to prune
Hydrangea serrata
Prune a mountain hydrangea in March, once the hardest frosts are over: only cut off the faded flower heads above the first pair of fat buds, and don’t shorten the other stems.
The mountain hydrangea (Hydrangea serrata) is a compact shrub of 1–1.5 m with graceful, flat lacecap flower heads: small, fertile flowers in the centre, surrounded by a ring of large showy flowers. It flowers mainly on last year’s wood: in winter the flower buds are already at the tips of the stems. Cut it back hard in spring and you cut off that year’s flowers. So pruning is mainly: old flower heads off, some dead wood out, and otherwise leave it alone.
| Pruning months | March |
|---|---|
| Nesting season (15 March–15 August) | Take care in March |
| Flowering | June–September |
| Good for bees, butterflies and birds | Yes, for bees |
| Native to Belgium | No, planted |
Mountain hydrangea: when to prune it?
Prune in March, once the hardest frosts are over and you can clearly see the fat buds.
Leave the faded flower heads on all winter: they protect the buds below from frost, and look lovely with hoar frost.
Don’t prune in autumn: the young buds would be left unprotected all winter.
What else to prune in those months? March
Mountain hydrangea: how to prune it?
- Cut off the faded flower heads just above the first pair of fat, healthy buds below the head.
- Remove dead, frosted and very thin stems at the base.
- Every few years, take out one or two of the oldest stems at ground level, so the shrub stays young.
- Don’t shorten the other stems: this year’s flower buds are at the tips.
- If a stem has been frosted a long way down in winter, cut it back to the first pair of green buds.
How much to cut, and how often?
- Every year: the old flower heads and the dead wood.
- Every few years, also one or two old stems at ground level, no more.
What does it mean for wildlife?
- March falls mostly before the nesting season (from 15 March). Hardly anything nests in a low hydrangea then, but do take a look if you are late.
- The small fertile flowers in the centre of the lacecaps attract bees, bumblebees and hoverflies. That makes a mountain hydrangea far more valuable to insects than a mophead.
- The dry flower heads shelter ladybirds and spiders in winter. Only cut them off in March.
- Combine it in partial shade with native shrubs such as hazel or guelder rose, which also feed caterpillars and birds.
Common mistakes
- Cutting all the stems back hard in spring, so that year’s flowering is lost.
- Cutting off the faded flower heads in autumn, so the buds get frosted.
- Never removing old stems, so the shrub fills up with thin, old wood.
- Cutting too low, below the fat buds, so that year’s flowering is gone.
Caution: It flowers mainly on last year’s wood: hard pruning in spring costs you that year’s flowers.
Nearby: related pruning guides
Plant profile: Mountain hydrangea · Pruning calendar and basic rules