Gadenin日本語Get the appPrune in late winter, because it flowers on new growth
Every flower this shrub produces is carried on wood that grows in the current season. That single fact settles the timing. Cut while the plant is bare and dormant in late winter, before the buds swell, and nothing you remove costs you a flower, because the flowering shoots have not been made yet.
The mirror image is also true, and it catches people out. Cutting in spring or summer, once growth has started, removes the exact shoots that were going to flower. A well-meant tidy-up in early summer is the most common reason a healthy shrub in full sun produces almost nothing that year. From the moment growth begins, the only cutting that belongs on this plant is removing suckers and shearing off seed pods after bloom.
Autumn pruning is a separate mistake. Cuts made in autumn push soft growth that will not harden before the cold, and that growth dies back over winter, leaving you with more dead wood than you started with. Wait for the bare, dormant weeks at the end of winter.
The plant leafs out extremely late, so a bare shrub in late spring is normal and is not dead. Scratch a shoot: green under the bark means it is alive. Do not prune it back hard in spring on the assumption that the wood has died.
How hard to cut: the flower size trade-off
This is the decision that actually shapes the display, and it is genuinely a choice rather than a right answer. Leave the shrub more or less alone and it makes a great many shoots, each carrying a large number of relatively small flowers. Cut it back hard and it responds by throwing fewer, thicker, more vigorous shoots, and the flowers on those shoots are dramatically larger, sometimes half again the diameter of those on an unpruned plant. The total number of flowers goes down; the size of each goes up.
Decide which you want before you pick up the pruners, then use the table to pick the level of cutting that matches.
| Approach | What you cut | What you get |
|---|---|---|
| No pruning at all | Nothing beyond dead wood | A large, dense, twiggy shrub covered in many small flowers |
| Light thinning | Dead, crossing and weak inward growth only | Natural shape, good flower count, an open airy structure |
| Moderate reduction | Last year's shoots cut back by about a third | Controlled size with flowers noticeably larger than unpruned |
| Hard pruning for size | Last year's shoots cut to two or three buds from the older framework | Far fewer flowers, but the largest the plant can produce |
| Renovation | The oldest third of the main stems taken to the base | Rejuvenates a bare-bottomed old shrub over three seasons |
| Training as a small tree | All low side branches and basal suckers removed | A clear multi-stemmed trunk with the canopy lifted overhead |
Making the cuts
Work on a bare plant in dry weather with sharp, clean tools. Because there are no leaves, you can see the whole framework, and the structural decisions become obvious in a way they never are in summer. Take the whole job in one session rather than trimming a bit at a time.
Whatever level of pruning you have chosen, the first three steps below are the same. The fourth is where the choice actually gets made.
- Take out dead, damaged and crossing wood first Cut dead stems back to living wood or to the base. Remove branches that rub against each other and any that grow back through the center of the shrub. Do this before anything else, and the plant is usually half pruned already.
- Open the center Thin out the thin, twiggy growth crowding the middle, cutting each piece back to where it joins a larger branch. Air and light through the center reduce the leaf spot and mildew that show up in a wet late summer, and they let flowers form deeper in the shrub instead of only on the outside.
- Take old stems out at the base if the plant is bare-bottomed An old shrub goes bare at the bottom and flowers only at the top. Cut the oldest third of the main stems right down to ground level. Repeat with another third the following winter, and by the third year you have an entirely renewed plant without ever losing a season of flowers.
- Shorten last year's shoots to the level you chose For a natural shape, leave them. For larger flowers on a controlled plant, cut each of last year's shoots back to two or three buds from the permanent framework. Cut a quarter inch (5 mm) above an outward-facing bud, on a slight slant away from it, so the new shoot grows outward rather than into the middle.
- Clear the base Cut off any suckers coming from the ground and any low side branches on the trunks if you are growing it as a tree. Rake out the old spent flowers and any fallen seed capsules while you can see the ground, because those capsules are next year's seedlings.
What not to cut, and what to write down
Do not shear the whole shrub to a flat surface like a formal hedge. It makes a dense shell of twiggy growth on the outside and a dead, hollow interior, and the flowers end up confined to a thin skin on the surface. Even when the plant is used as a screen, thin out whole stems rather than clipping the outline.
Do not cut into the old thick framework in the hope of reducing the plant's height dramatically in a single winter. It will respond, but with a mass of weak upright water shoots from the wounds. If the shrub is far too large for its space, take the renovation route over three seasons instead.
And do not prune once the buds have broken. From leaf-out until frost the shrub should be cut only for suckers and for seed pods after flowering. Shearing off the developing capsules while they are still green and closed is the one summer cut that genuinely earns its place, and it is what stops the shrub from seeding hundreds of nuisance seedlings into the surrounding border.
Keep a short record each winter: how hard you cut, and then, the following summer, how large the flowers were and roughly how heavily the plant bloomed. Two or three years of that comparison is the only way to settle the size-versus-quantity trade-off for your own taste, and it is far more useful than any general recommendation. Note the pruning date as well, since it tells you how many weeks ahead of leaf-out you were working.