Cutting Back Grasses and Perennials Without Wrecking Them

Cutback week might be my favourite work of the spring. The garden goes from winter-worn to ready in a day, and unlike most jobs in this trade, you see the whole result immediately.

Most of it is forgiving. But every spring we get called to look at a hydrangea that "died" or a lavender that never came back, and half the time the plant didn't fail. It got cut wrong. So here's the field guide.

Ornamental grasses

Miscanthus, switchgrass, feather reed grass, all the big ones we use for winter structure: cut the whole clump down to about 10 or 15 centimetres before the new green shoots get going. Wait too long and you're trimming around new growth one blade at a time, which is miserable.

The crew trick: cinch the clump with a bungee cord or rope first, then cut below it with hedge shears. The whole thing lifts away like a sheaf and cleanup takes seconds.

Blue fescue and the other small evergreen-ish grasses don't want a hard cut. Rake them out with gloved fingers and tidy the tips.

The hydrangea rule

This is the one to memorize, because the wrong cut costs you every bloom for the year.

Panicle and smooth hydrangeas (the cone-shaped ones like Limelight, and the big white Annabelle types) bloom on new wood. Cut them back hard now with a clear conscience. They'll regrow and flower on this season's growth.

Bigleaf hydrangeas (the pink and blue mophead types) mostly bloom on old wood. Those dead-looking sticks are holding this summer's flower buds. Leave them alone until late spring, then remove only what never leafs out. Prune them to the ground in March and you get a healthy green shrub with zero flowers until next year.

If you don't know which you have, wait. With hydrangeas, doing nothing is never the worst option.

Lavender and the woody herbs

Lavender is Mediterranean and it shows. Never cut it back into bare wood, because old wood rarely resprouts. Wait until you see new grey-green growth pushing, then shape above it. In our climate that's often late April. A lavender that looks dead in March is usually just late; one that got sheared to stumps in March is usually actually dead.

Roses and the forsythia clock

The old rule holds up: prune roses when the forsythia blooms. For shrub roses that means taking out dead wood, crossing canes, and shortening the rest by about a third to an outward-facing bud. Clean sharp cuts, and into the garbage with any diseased material, not the compost.

What not to touch at all

Anything that flowers in spring already made its buds last year. Lilac, forsythia, weigela in bloom season, magnolia, and the bigleaf hydrangeas above. Prune those right after they finish flowering in early summer, not now.

One more habit worth keeping: leave the cut stems from perennials piled loosely somewhere out of sight for a few weeks. Native bees overwinter in the hollow ones and they haven't all emerged by late March.

An experienced crew gets through a full property cutback in a morning, correctly, and it's one of the cheaper visits on our calendar. Book it alongside a spring cleanup and the garden starts the season exactly the way it should.