Yes, you read that right, pruning perennials. Especially with all the rain in New England recently (I did the rain dance and will take the blame), plants are experiencing incredible growth spurts. Although a lot of plants aren’t loving the deluges, and mold is spotting many of the stems and leaves, other plants are growing in leaps and bounds. And leaps and bounds results in lots and lots of flopping. Shrub branches have extended so quickly that their limbs are weak and drooping, and plants are reaching skyward only to be toppled over by heavy winds and more rain. So, what’s a gardener to do? Start by grabbing your pruners and heading out into the jungle that was once an orderly garden . . . and may the force be with you.
Many of our late blooming (taller) perennials are prone to flopping under the assault of wind and rain, and if you’re like me you don’t have the time (or the inclination) to go about staking everything. But there is another option that works quite well if done at the right time: pruning your perennials. Candidates like ironweed, joe pie weed, tall varieties of rudbeckia, helianthus, phlox, and bee balm will bounce back from a pretty hard pruning and still produce gorgeous flowers as if nothing ever happened. The trick is in the timing and determining how much to take off, which comes with trial and error.
I learned about pruning perennials from Tracy DiSabato-Aust’s book: The Well-Tended Perennial Garden, which is a great book overall with lots of helpful advice for novice and experienced gardeners (visit: www.tracylive.com). Tracy is an author, designer and triathlete, and when I met her years ago, was not what I expected a hands-on gardener to look like: that is, wearing tight leather pants, makeup, well manicured nails and long blond hair in cornrows. Appearances aside, Tracy knows her stuff when it comes to design and maintenance, and she came up with a good technique for keeping taller perennials in check.
Tracy (a passionate pruner) dedicates 43 pages of her book to pruning perennials; deadheading, cutting back, pinching, and seasonal pruning. She also provides an extensive list of perennials with brief descriptions and suggested times and methods for pruning. Here are some of the plants from her list that will benefit from a trim earlier in the season: asters, coreopsis, dianthus, echinacea, eupatorium, helianthus, heliopsis, monarda, nepeta, phlox paniculata, rudbeckia nitida ‘Herbstsonne’ and fulgida ‘Goldsturm’, solidago, vernonia noveboracensis, and veronicastrum.
My reason for pruning perennials is simply to prevent flopping and promote healthier, lusher growth. Since reading Tracy’s book, I have been faithfully pruning annually. Basically, if you consider the bloom time, you will be able to figure out the best time to prune a perennial. For earlier bloomers like nepeta, I will cut back by a third to half after the first bloom. Usually it has started to splay open and the trimming freshens it up and promotes a second flowering. This year I’m experimenting with one nepeta ‘Walker’s Low’ that I cut back to about 4″, to see if it flourishes or flounders (stay tuned . . . same bat channel). I have had great success pruning my tall guys such as rudbeckia nitida ‘Herbstsonne’, eupatorium (Joe Pie Weed), helianthus ‘Lemon Queen’, heliopsis helianthoides ‘Prairie Sunset’, vernonia noveboracensis (ironweed), and veronicastrum virginicum, when they are cut back about a third by mid to late June. If they are particularly leggy by then, I may cut back by half. All of the aforementioned plants have still bloomed beautifully as if there had been no intervention on my part. Although Tracy has had luck with pruning late season phlox, my phlox paniculata ‘David’ was not at all happy after it was trimmed and produced noticeably smaller blooms that year. Usually phlox stands quite nicely without pruning anyway, but try clipping and see what your outcome is.
Montauk Daisy (Nipponanthemum nipponicum) is an ongoing process in my garden. I usually prune it back with the others in mid-June, but it may require a second shear in late July to prevent the legginess it is so prone to. I’m still experimenting with this one, last year I missed the second prune and all the stems were weak and bent over (although it was loaded with flowers). Part of the problem is that Montauk Daisy has an unpleasant odor and I really dislike pruning it-the good news is the other critters find its scent equally offensive as well.
Shrubs will also benefit from a gentle trimming, however you may sacrifice some blooms in the process of pruning weak limbs. I have found that dwarf willows, twig dogwoods, smoke bush and dwarf cranberry viburnums seem most prone to falling and spreading apart from the weight of multiple storms. They benefit quite nicely by trimming back some of the lower branches and then alternately pruning back some of the weakest inner branches. Depending on when you trim, berries may be lost on the limbs of twig dogwoods and cranberry viburnums, so you may decide to wait until after the birds have indulged in their fruits before tidying things up.
So, my friends, try a little experimenting with your pruners. Clip some stems to different heights to vary flowering times. Prune some plants down and see how they respond. Shear off some of the upper layers to reveal fresh growth underneath. And most of all, have fun!