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.
Forsythia in thicket mode
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
Please don’t.
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.
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Oh dear. I hoped to get advice on a monster heirloom spirea.
It’s about 6 feet circumference at center base, and 40 feet around. I’m in zone 6b Maryland and it just finished blooming, May 14th. Now that it’s the 24th, will a 3 foot circular cut remove next years flowers? I really want to shave deeper, like 5 feet in.
Full sun Apr to Sep then sun moves south of 2 story house again.
I want to plant red Azaleas around the dripline for the weeping Spirea to droop into, and keep winter blowing leaves out from under.
Hi Teena,
No worries… the “best pruning time” window is short but it isn’t THAT short.
If the 6 feet at center base is the extent of the stems, with the 40 feet being the outer reach of their tips, reducing the base to 5 feet in circumference should be fine, though you may find when you get in there that the center is weak or dead, in which case you’d probably be wise to dig out the dead material, apply fresh soil and be sure the inner edge is trimmed back enough to permit light to fall on the new sprouts that would be sent to colonize.
Interesting idea about the azaleas; is the spirea tall enough to shade them during the summer? Many spireas can do well with less sun than advertised and there are many azaleas that can take more sun than you’d think, but light needs are definitely something to keep in mind when you go shopping.
also please keep all of US in mind and write back with progress reports! The Heap is feeling very outclassed in the gigantic department.
Sorry this answer is so long coming. I had a little brain fog. The Spirea is a good 5 feet tall with sprigs to 6 feet. Once the sun moves to that side of the house, it goes straight over. So one side gets morning sun and the opposite side gets afternoon sun which is to hot.
I’m in Maryland with red clay ground, so to solve this I dug a half moon trench. Two feet wide and 2 feet deep. Using my mulched sycamore tree leaves, mixed 2 parts leaves to 1 part soil. This essentially makes an in-ground container for the azaleas (as the unamended clay acts like concrete) to put plenty of water in. I have a short piece of roof right there (about 10 feet) so I led that drain to the trench. (It is mindboggeling how much free rain one can get off a roof).
I used those same mulched leaves under the Spirea. First after hand weeding, I layed 10 sheets of newspaper, then about 5 inches of mulched leaves. That solved all weed problems under there and it keeping it more moist and more worms come and aerate. A red brick curve around the Spirea tells me that 5 inches reduced to 2 inches in a year. So I just add more – without having to weed or use newspaper again.
Now, about the Spirea itself. I don’t think cutting it back accomplished anything. 2009 and 2010 the tentacles didn’t drip down to within 2 feet of the ground. I expect it will in 2011, but by that time the plant will be FULL SIZE again. I guess it’s not a bad thing. That red brick curve leads you from the back yard to a 30×30 side patio.
The huge Spirea makes it a blind turn, and people are always thrilled to find another completely different garden there, with Nikko Blue Hydrangeas, a huge white Dogwood, a 5×30 foot slope with honeysuckle, 10 foot tall Hydrangea (with football size & shape blooms) on each side of an 8 foot arbor which shade White Moonflower and Old Fashioned Blue Morning Glory just enough that they bloom ALL DAY and grow over the arbor. A 4 foot fence on the afternoon side protects them too. This was truly a unique event as a “normal” moonflower only flowers in moonlight, and “normal” morning glory bloom about 30 dang minutes in the morning. My friends insist it is NOT a unique event, but that I threatened them, which I admit isn’t entirely untrue. But mostly I use positive reinforcement, like OMG you truly are a morning glory ALL DAY LONG – look at you next to moonflower!! A couple of urns on each side of the arbor gate is full of velvet Red Mandavilla and complete the picture. I even employ a rectangular umbrella to shade the Nikko Blue Hydranges from the morning summer sun, to keep from bleaching them out. One in the corner never bloomed as it had to much tree shade. I pruned the tree and the next year it grew to 5 feet and had deep purplish blue blooms. I swear it looked down at itself and said OMG – I’m a Hydrangea! Yes you are! With royal purple blooms and leaves bigger than my head! You go girl!
In truth, it’s the last plant for the sun to clear the corner of the house and start beating on it and fading it.
But I don’t tell her that. She waited 5 years to bloom and deserves to think she’s “special”.