Pruning Forsythia, Spirea, Mock Orange, Fragrant Viburnum, Ceanothus…
Or, Pruning spring-blooming shrubs that grow as thickets of svelte trunks and slender stems, because although they have their differences they all behave pretty much the same way.
Flower buds form during the summer, mostly on one and two year old wood, so the standard advice is “prune right after bloom.” That way there’s maximum time for next year’s show to get itself together.
But after years of following that advice I started doing something that’s more fun and just as good or better from the pruning standpoint: making big bouquets.
In other words, “prune ‘em while they’re blooming.” Pruning when the plant is in flower not only turns a chore into a pleasant experience and decorates the house with unimpeachable flowers, it also enables you to see exactly which growth is being most productive on that particular shrub.
A forsythia in partial shade, for instance, may bloom most generously on 2, 3 and even 4 year old wood. A spirea in a sunny spot may just keep pumping out the ones, while older growth rapidly gets twiggy and unappealing. Even very common plants have individual personalities; the closer your acquaintance with each, the better the pruning job is likely to be.
Of course pruning is as much – or more – about shape as it is about flowers, and here is where we have to start by saying
No, really, it isn’t a wise idea. There are about two extremely sophisticated garden designers who might be able to get away with this, in a severe modernist setting that features a lot of very expensive hardscape.
Absent that sort of special circumstance, the shape to aim for with loose growers is natural plus. Natural being weeping in the case of forsythia and spirea, upright for mockorange, viburnum and ceanothus. The plus is the gardener’s tactful enhancement of that natural shape.
Whether upright or weeping, the plant is inclined to form a dense twiggy mass with lots of dead wood inside. Pruning is editing, not creating; basically you just want to loose the mess.
Most of the time, this means removing both the oldest trunks and the newest shoots. Not all the newest shoots, obviously, or you’d never get blooming wood (or much of anything else) but until the plants get quite old, they send up too many new sprouts for the space allotted. If you leave just one for every old trunk that will be removed next year, the plant will be stronger and better looking.
All the extra new shoots come off right at ground level and so do most of the old trunks that no longer produce much bloom. But the standard advice to always remove old growth at the base is, like all standard advice, a little too standard. It’s the right move most of the time but does not supersede the first rule of pruning: always let the plant tell you what’s happening. If there’s a graceful combo of old trunk with mega-blooming new branch or branches you might as well leave it alone.
For diehard fans, here’s a post that focused on forsythia , all by its cheering golden self.