It depends entirely on which type of hydrangea you have. Some bloom on last year’s branches (“old wood”), so cutting them back at the wrong time can remove next year’s flowers.
Here’s the easiest guide:
| Hydrangea type | When to prune | How much |
|---|---|---|
| Bigleaf / Mophead (Hydrangea macrophylla) | After flowering, usually summer | Light pruning only |
| Lacecap | After flowering | Light pruning only |
| Oakleaf | After flowering | Light pruning |
| Mountain hydrangea | After flowering | Light pruning |
| Panicle (‘Limelight,’ etc.) | Late winter–early spring | Can cut back considerably |
| Smooth (‘Annabelle,’ etc.) | Late winter–early spring | Can cut back considerably |
| Climbing hydrangea | After flowering | Trim only as needed |
If you have the common blue/pink/purple hydrangeas
These are usually bigleaf hydrangeas, and I would not cut them way back in fall or winter. They typically form next year’s flower buds on stems produced this year.
After flowering:
- Cut the spent flower head off just above a healthy pair of leaves/buds.
- Remove dead, broken or obviously diseased branches.
- If the shrub is getting crowded, remove a few of the oldest stems all the way to the ground rather than shortening every branch.
- Avoid giving the entire shrub a “haircut.”
Panicle hydrangeas are different
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If you have something like Limelight, Little Lime, Bobo, Vanilla Strawberry or Quick Fire, they’re much more forgiving. They bloom on new wood, so you can prune them in late winter or early spring before new growth gets going.
You can generally shorten last year’s growth by about 1/3, remove weak skinny branches and crossing branches, and shape the shrub. A harder pruning is possible, but you don’t need to cut them to the ground every year.
What I’d do right now in Oregon
Since it’s the end of August, I’d be conservative. You can deadhead spent blooms and remove truly dead wood, but I wouldn’t heavily prune an unidentified hydrangea now.
