Gadenin日本語Get the appTwo rules that decide everything
Almost every pruning mistake made on this shrub comes from ignoring one of two facts. The first is that the flower buds for next spring are formed on wood that grew during the current season and then sat through winter. By late summer those buds already exist along the upper side of last year's shoots. Anything you remove after that point is removed with the flowers attached, whatever the plant looks like at the time.
The second is that the horizontal branching is not a side effect, it is the plant. Growth is produced in flat tiers stacked one above another, and the flowers sit along the top of each tier so that the shrub reads as a set of white layers rather than a mass of blossom. A plant clipped to an even outline loses that structure permanently, because the tiers are made by long unbranched extensions that shearing cuts off every year.
Put the two together and the pruning policy writes itself. There is one short window, immediately after the flowers fade, and inside that window you cut as little as possible and only ever by removing whole branches back to a junction. There is no version of this shrub that responds well to being trimmed.
The window, and what happens outside it
The correct moment is the two or three weeks that begin when the last flower heads have browned and end before the plant has put much summer extension on. Cut then and the shrub has the whole growing season to make new wood and set buds on it. Cut a month later and you are removing wood that is already committed to next spring.
The table below is the honest account of what each timing costs. It is worth reading before you pick up the saw in autumn tidying mode, which is when most of the damage to this species is done.
| When you cut | What it costs | Verdict |
|---|---|---|
| Immediately after flowering | Nothing; a full season to rebuild | The only real pruning window |
| Midsummer | Some of next spring's buds, and the tier tips | Only for dead or broken wood |
| Late summer to autumn | Next spring's display, and any berries | Avoid entirely |
| Winter, dormant | Next spring's display; tiers cut back to stubs | Dead wood and beetle eggs only |
| Early spring, buds swelling | The flowers you are about to get | Too late; wait and cut after bloom |
Light pruning, branch by branch
Work with hand pruners and a pair of loppers, and leave the hedge shears in the shed. Every cut should end at a fork, so that the branch you shortened still finishes in a growing point rather than a stump. Stand back after every third or fourth cut, because on a tiered plant the damage is done by accumulation rather than by any single mistake.
- Take out dead and crossing wood first Remove anything broken, dead or rubbing against a neighboring branch, cutting back to the parent branch. On a healthy plant this is often the whole job, and it costs no flowers at all.
- Shorten a tier by removing its end, not its outline If a horizontal branch has run too far, follow it back to a side branch that points in the direction you want and cut there. The tier keeps its flat plane and its tip growth, just at a shorter reach.
- Thin, do not reduce Where tiers have crowded into each other, take out an entire branch at its origin rather than shortening several. Space between the layers is what makes the flowering read as tiers, so removing wood is more useful than trimming it.
- Lift the lowest tier only if you must The bottom layer often rests on the ground and roots where it touches. Cut it off flush at the trunk if it is in the way, and accept that the shrub then reads as a small tree rather than a mound.
- Stop at about a fifth of the plant Removing more than a fifth of the live wood in one season pushes out vertical water shoots that spoil the layered shape for two or three years. Spread bigger jobs across successive seasons.
- Note the date you finished Record the date the last flowers browned and the date you pruned. Two or three years of those pairs tell you exactly when your own plant's window opens, far more reliably than any general advice.
Never use hedge shears or a powered trimmer on this shrub. A single shearing removes the flowering wood and the tier tips together, and the dense twiggy shell it produces then shades the interior so the plant cannot rebuild the structure from inside.
Recovering a shrub that has been clipped
A plant that has been sheared for years is a dense ball with bare wood inside and flowers only in a thin skin on the surface. It can be brought back, but the process runs over three or four seasons and the shrub looks worse before it looks better.
Work only in the after-flowering window. In the first season, cut two or three of the oldest main stems out at the base and open holes through the twiggy shell so that light reaches the interior wood. In the second season, choose the strongest of the shoots that respond and remove the rest, keeping the ones that leave the trunk at a wide, near horizontal angle. In the third and fourth seasons you simply let those chosen branches extend and stop cutting the tips.
The one thing that will not work is renovating by cutting the whole plant back hard at once. Japanese snowball resprouts unevenly after that treatment, sends up a thicket of vertical shoots, and takes several years to flower again, and the vertical growth never recovers the horizontal habit that was the reason for growing it.