pruning roundup: what shrubs i prune when

lilac-pruning-2WHAT NOT TO DO IS AS IMPORTANT many times as what to do each season, the dont’s as powerful as the do’s. Nowhere is this more to the point than with pruning, the “there’s no turning around now” portion of horticulture, where you can’t glue it back on or wait a few weeks for another (forgiving) flush of foliage, as when you give a ratty perennial or annual a needed haircut. Are you feeling scissor-happy? Read this first.

Each May and June I’m asked, “Why didn’t my lilacs bloom?” only to find out in the next sentence that the questioners had literally nipped the plants in the (flower)bud with late summer, fall, winter or earliest springtime pruning, long after the new year’s blossoms had been set.

Early bloomers flower on old wood. Go out and look at a forsythia or a lilac: Unless you pruned in summer or fall, you’ll see flower buds already in place, dormant but there. If you prune now, it won’t flower now. Make sense?

Generally speaking, don’t prune spring-blooming shrubs and trees more than a month or so after they finish blooming. After they’re finished flowering, prune immediately. You will not kill the plant by pruning a little later, in many cases, but you will be deprived a season of bloom, so why not first enjoy it?

Woody plants that flower late in the season, such as Hydrangea paniculata, bloom on new wood. Again, go out and look. You don’t see any flower buds now, in early spring, do you? Discovering where on the stems and when the plant creates its flower buds will help direct your pruning efforts.

Details, details:

Lilac pruning: Unless the shrub’s a neglected wreck in need of rejuvenation, cutting off bouquets of flowers is all the pruning you’ll want to do. I never prune them here in my Zone 5B climate after July 4, and like to finish up earlier. The details are here (and there’s a glossary of my favorite varieties, too).

Viburnum pruning: Less is more. Please don’t think of my favorite genus of shrubs (and great bird plants, too) as hedge material to shear and mutilate. Here’s the protocol.

apple-pruning-2Fruit-tree pruning is an exception among early bloomers: With apples and the like, what you’re working toward isn’t as much the pretty flowers as an architecture and openness that can carry and ripen maximum fruit. I prune in late winter, knowing those are apple blossoms-to-be I am cutting off. Read my method.

Roses: If I had any (well, I have three, mostly R. rubrifolia that I grow for its blue foliage) I’d be on the alert right now, as winter transitions to spring. Many common kinds of roses are pruned when the forsythia blooms. Read how the pre-eminent rosarian of the day, ex-Brooklyn Botanic Garden rose-garden curator Stephen Scanniello, approaches it.

Clematis: I like the ones that like to be cut back hard in spring, to about 18 inches (and frankly I treat a lot of others this way, perhaps delaying their bloom time but never seeming to kill them). Here are a few I deal a heavy hand to, and one that blooms in early fall that I am similarly harsh with.

Weigela: Some shrubs, including weigela, hate being cut back part way, and are better pruned thus: Remove a portion of the oldest stems near the base, to allow younger wood to develop fully. Weigela look a mess when cut back at midpoint, as do Buddleia. If the weigela has really outgrown its space, cut the entire plant to about 12 inches from the ground right after flowering (or earlier spring if you like, skipping the bloom) and it will regrow.

Buddleia: Off with its head, now. Just before the buds want to break, cut the most familiar kind, B. davidii down to near ground-level. Even though in some gentle winters it seems as if it will break higher up, it will look like a hell of a mess without a hard cutback, trust me.

Twig dogwoods and twig willows: Grown for their colorful twigs (you can see some of mine in fall with golden crabapple fruit here), these tough creatures can be cut to near the ground every few years if they grow out of bounds, or you can thin selectively, removing some older stems at the base to let new ones come through. If their color isn’t as good anymore, give them a thorough cutback, or stooling, to promote younger more vibrant wood. Prune in late winter or earliest spring if needed.

Hydrangeas: I’m going to leave this hot topic for a whole separate story, but generally speaking, prune the mopheads (H. macrophylla, the big blue ones) after they bloom in summer, but before they set next season’s buds. How? Cut out the oldest stems to the ground to make room for new ones. This one’s a trickster to normal thinking, because though it blooms relatively late, in most varieties it does so on year-old wood, so it does carry flowerbuds over the winter. Deadheading is always allowed.

peegee-pruningWith Hydrangea paniculata, the Pee Gee (what we commonly call H. paniculata ‘Grandiflora’) and ‘Tardiva’ and other panicle types, a different thinking: they bloom on new wood. Prune them in late winter or early spring, just before new growth begins. (You can even prune in late fall, but I don’t like to do it until after winter has made its mess, in case branches are lost in storms.)

They can be cut back quite hard, and still make new wood that then gets buds and blooms. Or you can skip pruning altogether, if you like.

Where to place your cuts can be confusing. I have had ones I didn’t cut back enough turn to octopuses (octopi?) and really look a mess, and this is inclined to happen on older specimens that have been cut back again and again. I’ve also cut old ones back too hard and had to suffer through some gawky recovery years.

The “secret,” if there is one: To get a good-shaped plant, you will often be cutting back to a mixture of oldest (thicker) wood and younger (last year’s) wood, which is counter-intuitive. The pruned structure will look odd, but try to think only in terms of creating a framework for emerging shoots that will then be topped with flowers. Your cuts indicate to the plant where it should (please) sprout from. Let go of the fact that the wood you’re leaving will be of varying thicknesses, not some perfect-looking architecture.

As for the oakleaf types, I either don’t deadhead at all or if they need pruning I do it right after bloom–not later. If they are overgrown, take out some of the oldest stems at the base, as with the blue mopheads. When I used to grow H. arborescens ‘Annabelle,’ I cut her to the ground each year (like the panicle types, she blooms on new wood, so how much you prune is up to you).

Want to hear the contrarian position on hydrangea pruning? As with all gardening, part-art and part-science, here is one, and it’s from a very impressively credentialed individual, Dick Bir of North Carolina State University, whose point of view is summed up here.

And then there’s just the matter of general pruning: Anyone can do at least a good job of basic pruning. Not doing anything is much worse than following these easy steps.

One time I never prune anything hard: in fall. Encouraging new shoots so late in the season is inviting damage to soft new tissue when frost comes. So I time all big rejuvenations for early to mid-spring. But each in its good time. Agreed?

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March 20, 2009

comments

  1. says

    I confess that I was feeling guilty (and scissor ready) because I did not prune anything last year. Thanks for the great advice. Now I know what not to do with my lilacs.

    • says

      Welcome, Elsa. When I am feeling overwhelmed I remind myself: Go out and look at the branches and see what the plant is trying to tell me. (Sometimes I still get overwhelmed, but usually it helps guide the way.) Glad to see you, and hope to see you soon again here.

  2. says

    Thanks for the tips Margaret. I’ll see if I can tell the difference on my Hydrangeas. Any suggestions for over grown Cranberry Viburnums? Every Spring I can’t bring myself to prune them and now they’re 12″ tall. I may have to bite the bullet this Spring and the be ruthless.

    Thanks for a terrific site.

    Russ

    • says

      Welcome, Russ. Funny you should ask…I have butchered overgrown cranberrybush viburnums and their close cousins, as I confessed in last year’s viburnum-pruning post, I think. Right now (or pretty promptly, before growth begins preferably) cut them down near the base. Brutal, yes, but they will regrow (or at least mine have). Whatever you do, don’t go halfway with them….what a mess. Brutish is better. See you soon again.

  3. Pam S. says

    Hi There – I’m in Washington, DC .Do you have any advice on when to prune a fig tree/bush (i.e., one of ours is rather bush-like with multiple trunks, and the other has one main trunk). They grow lots of leaves, but we are having trouble getting good fruit crops. We’re wondering whether some judicious pruning in the fall might lead to a stronger, denser growth with more fruit in the spring. We wouldn’t prune right now as whatever ever fruit there will be has already developed on the current branches and buds. We also wonder if there is anything to use as feed/fertilizer to help it set and ripen more fruit. By the way, I know that this is not just a geographic area problem as a friend has several figs that bear heavily all summer. His original plants came from Italy, sent by friends in the mail (basically just as “sticks!”). I am thinking that it may be all, as real estate agents say, an issue of “location, location, location!” The figs are located in safe, protected spots against walls (and thus winter over quite well), but perhaps they’re not getting enough sun per day?

    • says

      Welcome, Pam S. I have never grown figs, owing to my climate, though technically there are some I could try if I protected it in winter, like this one. SO I have no first-hand experience. Were I to try, I’d probably start on this wild but information-filled website, Figs4Fun, which has growing information and so on, and also this more horticultural how-to from the Royal Horticultural Society in England as a start, and see what it adds up to (full sun, heavy feeding, it sounds like, and according to the RHS a deliberate pinching/pruning system). The growers’ group recommends specifics on the fertilizer and soil ph. And you never know, I may do some homework and learn more along with you. See you soon again.

  4. Karen Z says

    Hi Margaret, love this information. I’m in Australia and I cut my buddlia davidiis back after flowering but I also have 2 that flower late winter (not late summer). They were here before we moved in and had probably never been pruned and the bases are very thick. We get cold winters but no snow. When should I prune and how much should I take off? Happy First Birthday! Karen

  5. Doretta says

    I happened on your website and i love it. I am learning allot about what I don’t have down here in new orleans to grow. All the things i lust after…peonies lilacs etc…you get the drift….no seasons but always flowers and green… much different gardening than yall…I am always amazed and infatuated with the differences…so it is a little like a foreign language reading about yall’s gardening..but the desire is the same!

    • says

      Welcome, Doretta. I have been to many gardens around Louisiana, and what I remembr most was the oakleaf hydrangeas, and how giant they grew there and how beautiful. (That was the first place I ever saw one, like 20 years ago.) Thanks for your visit and do come again soon. We will share our lilacs with you soon. :)

  6. Emilie says

    Hi, Margaret! My husband’s problems have begun to overshadow the pleasure of gardening. But I’ve cleaned up all the winter debris and even planted some seeds (lettuce, snow peas, parsley). I’m slowly bringing my neighbor’s lilac back to life. The few thick branches left by a terrible pruner years ago are dotted with thick buds. I’m wondering if I should cut it back even further to encourage growth lower down. There’s clearly a lot of life left in it that just needs a chance. I’m also wondering when and how one should prune holly (ilex). When, I assume, is now. But how when they’re fairly shapeless? Their maximum height at the moment is about 4½ feet.

  7. says

    Really great information and links, Margaret. I know a lot of gardeners will be bookmarking this page for later use. I put it in my ReadLater box myself. Always good to check when I’m not sure. However, I think I’ve got the rose pruning down after all this time. LOL.~~Dee

    • says

      Hi, Dee…and yes, I expect you might be on auto-pilot with the rose care over there. Here, not so much; I have to talk myself (out loud) through the angle of the cuts, since I have so few roses to practice on. Each to our own addictions, right? Happy spring.

  8. suzanne says

    Margaret:
    Love your site, what is your opinion on crepe myrtle in Northern NJ? Any particular species and if I have partial sun about 4-6 hours- is one species better than another for this area?

    • says

      Welcome, Suzanne. Local nurseries will be able to guide you as to cultivars that are a bit hardier, which is probably all they would dare stock (such as the various ones from the National Arboretum breeding program). Read the middle portion of this page from their site. I am so cold I do not even try them, but have seen magnificent ones on Long Island and elsewhere near NYC.

    • says

      @Suzanne: This one slipped by me, sorry. Spring! I have seen them grown in the NY metro area, particularly on Long Island where it is more temperate, especially some of the kinds that the National Arboretum introduced over the years for extra hardiness and other good traits. You might browse through them here. Often, though, in marginal areas they are grown more like “cutback shrubs” (either cut back by the gardener or the winter!) but they quickly regrow and bloom.

      You won’t get the wonderful trunk and bark if the plant gets hit by winterkill, of course.

      The information about which species and varieties are how hardy is on the page. The late Jim Cross of Environmentals Nursery on Long Island grew them beautifully, and they achieved tree proportions; details here.

      I would try to get one from a local source so that it’s a variety the nursery has tested locally. If you want that look of a tree with plumes of late flowers, you could try Heptacodium instead…not the same (and white-flowered) but sometimes called the northern crape myrtle. :)

  9. wicki Boyle says

    Margaret
    You say to deadhead the daffodils now because of the terrible heat. OK when I cut do I cut below that bulbous thing just under the throat of the flower or leave it and just snip the actual flower. I know the leaves feed the plant so do tell
    THanks
    WIX

    • says

      @Wici: I just snap off the spent flower iteself with my fingers (you can also use a snips/pruners of some kind) but I leave the entire flower stalk and all the foliage until about July 4, when it starts to wither of its own accord. The Flower-Bulb FAQ page has full information about this aftercare.

  10. liz says

    here are my pruning stories – i’ve inherited my family’s messy falling apart house in Brooklyn which came with an overgrown back yard which is contains a fig tree. it also had branches more suited to an octopus. it had grown figs in the past but had seemingly stopped. we loped of fbranches in an attempt to get rid of it and lo and behold! fruit in the late summer last year. have done some more judicious pruning – late fall last year and keeping my fingers crossed for more fruit this year. we don’t wrap it as i have seen advised in some articles. it seems OK with the cold NYC weather.
    paniculata hydrangea – hugely overgrown with only one flower last summer.totally confused about when and how to to prune plus i had had enough of the unruly bushes and plants so i chopped it all down to about 8 inches.waiting to see what happens.
    peony bush (which i love) had mildew so i pruned it way down and i see new growth coming in – hooray! need to move it to a better site.i hope doing it this spring won’t be a bad thing.

  11. Mary Jane says

    Planted my first Rose of Sharon last year; abt. 4′ tall. Do I prune her; ever?

    How abt. transplanting young mop-top hydrangeas? Is now OK? Thanks to you, I got my first paniculata last year and she’s coming back v. nicely. (She who will not be pruned.)

    Thanks for everything, have the best of Springs.

    PS You had a quick vegetable stew recipe this fall/winter that was a lifesaver.

    • says

      @Mary Jane: Rose of Sharon can be pruned to stay in bounds (or left t grow almost small treelike if you prefer). Prune to limits its size just before it starts to come alive and leaf out in spring, so now here. You can cut it back to a few feet tall, and it will regrow a couple of feet a year or more…or if really out of control, you can rejuvenate it even more severely, taking out stems or the whole plant to near ground level for a fresh start. So it’s about what yours looks like — keep it the shape and size you want it, from shrubby to quite tall.

      As for the transplanting, I do it when I can — early spring and early fall are my favorite times for moving things (because cooler, moister days usually) so yes, move it. I know, it can cause a hiccup…but better to get it where it belongs and let it start settling in.

  12. Photosensualis-Sally & Michael says

    We’re a little late climbing on board, but thanks for your inspiration and permitting us to visit your beautiful garden!
    Sally & Michael

    • says

      Welcome, Photosensualis (aka Sally and Michael). It was nice to see you, too, and I hope we will catch up again as this wacky season progresses. Brrr!

  13. Dana says

    Hello, Margaret! Novice gardener with a question for you: any thoughts on how or when to prune Mallows? I’m in Southern California, so in quite a different clime from yours, but thought perhaps you’d have some insight. So thrilled to have stumbled upon your website and podcasts — you provide a wealth of information and interest! I’m a newly minted fan. Best, Dana

  14. Amy Lewis says

    I have been experimenting with pruning Hydrangea ‘Limelight” and was not happy with my last years results. I pruned them back by 2/3 as I wanted to control their size. They line a driveway, 23 on each side. What I ended up with was tons of very elongated branches with very large blooms making them top heavy . I am thinking I will cut them back even harder this year…maybe 18″ but am feeling timid. Any thoughts.

    • says

      Welcome, Amy. The paniculata hydrangeas can be tricky to learn to prune to the shape you desire, even though it’s hard to kill them and they put on so much new growth each year.

      Start by reading the part about them in this Fine Gardening article. My pruning FAQ has a section on them, too, with a link at the end to the instructions from Dick Bir of NC State Extension.

  15. Barb says

    My witch hazel is happily blooming now. There is a good 30 percent of the shrub tht has no blooms and I wonder if these are simply immature and will blossom in later years…or are they sucker stems that need to be pruned. Any advice?

    • says

      Welcome, Barb. Do the twigs that are not blooming look different from the others (bark, how straight/thick they are, the directional they come from/point?). Sometimes on witch hazel and many other grafted shrubs, the rootstock starts sending up stems that need to get cut out completely to the base as they emerge, preferably. Could that be it?

  16. Barb says

    You certainly asked the right questions – the other branches are smoother bark and have almost no branching than those that are flowering. I’ll mark them now and when the flowers fade, they are going to be trimmed out. Last year we had some sort of fungus on this shrub and on some vibrunums. I plan to spray them when they leaf out – any advice for treating fungus organically? Thanks!
    -Barb

    • says

      Perfect, Barb — that’s what I suspected you would see/say. As far as fungus on Viburnum, of which there are various kinds I believe, I haven’t tried to treat/control it here, no. I see that Clemson has a bulletin that explains some types, their causes and what to do…looks like horticultural oil works for some issues but that sulfur sprays cannot be used on Viburnums, e.g. See if you can determine which issue you are having.

  17. Steve - Troy NY says

    thanks for the info. One thing about the paniculata hydrangea – after cutting back I frequently divide and multiply the number of bushes I have as a way to expand and control. I am finally going to follow your weigela advice and really cut them back. (again, a great website resource I look forward to seeing)

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