Pruning Perennials

Helianthus 'Lemon Queen' in A Garden For All by Kathy Diemer

Helianthus ‘Lemon Queen’ along fence (photo: Kathy Diemer)

Many of our taller, late blooming perennials are prone to flopping or collapsing under the assault of harsh summer 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 an 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. Here’s a few tips that have worked well in my challenging New England Garden:

Joe Pie Weed standing tall in A Garden For All by Kathy Diemer

Joe Pie Weed standing tall (photo: Kathy Diemer)

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 both novice and experienced gardeners (visit:  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.  Donned in tight leather pants, makeup, well manicured nails and long blond hair in cornrows, you may not take her seriously, yet Tracy knows her stuff when it comes to design and maintenance, and I use several of her techniques to keep my taller perennials in check.

Rudbeckia nitida 'Herbstsonne' in A Garden For All by Kathy Diemer

Rudbeckia nitida ‘Herbstsonne’ (photo: Kathy Diemer)

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.

Nepeta 'Walker's Low' in A Garden For All by Kathy Diemer

Nepeta ‘Walker’s Low’ in front of border (photo by: Kathy Diemer)

My reason for pruning perennials is simply to prevent flopping and promote healthier, lusher growth. Basically, if you consider the plants bloom time, you will be able to figure out the best time to prune.  For early blossomers like nepeta, I will cut back by a third to half after the first flush.  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 Daisies in A Garden For All by Kathy Diemer

Montauk Daisies (photo credit: Kathy Diemer)

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.

Trim to Fit in A Garden for All by Kathy Diemer

Various shrubs pruned to fit (photo credit: Kathy Diemer)

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, experiment a little 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!

**To find out more about pruning shrubs read A Time to Prune


  1. I was wondering what happened to Tracy. For a while there she was very visible on the garden scene. I saw her speak at a Mass Hort meeting many years ago and probably again at CT Hort. Apparently she juggles compulsive activies. Not unlike most extreme gardeners that I know.

    Her first book is a fabulous reference but I really enjoyed the Well Designed Mixed Garden. Based on her advice I also prune quite a few perennials. Like you, I’m not much for staking plants. Nepeta ‘Walkers Not So Low’ gets a haircut before it’s first bloom and again after. So far so good. Maybe tonight I’ll go home and pull one of her books off the shelf.

    • Did she have the leather pants when you saw her? Ha Ha. I haven’t seen her since early 2002-03 either. I laughed out loud at “Walkers Not So Low” — for sure that name is inappropriate! However, I did cut one back to 4″ and it appears to be coming back quite nicely, so that may be my new technique with them. Thanks for writing, Sue. I always enjoy hearing from you. And I hope you and your gardens are faring well during this hot spell~

      • Yes, I believe she may have been wearing leather pants. A talented garden designer-her style reminds me alot of Hayefield’s Nan Ondra.

        Fortunately I think this hot spell (humidity…ugh) may be over for the time being. So far the garden is faring better than me. 🙂

Speak Your Mind