from the forums: pruning viburnums

WHEN TO PRUNE VIBURNUMS? That timely question was raised this week on the Urgent Garden Question Forums. “When is the best time to prune large viburnum shrubs?” asked Forum member ZSteinberg. “Two are double-file, three are American cranberrybush and I don’t know the names of the other three. Any general recommendations?”

I have grown a lot of viburnums over the years, and have pruned them at various times of year for one reason or another. Usually viburnums need relatively little pruning, assuming you planted the right cultivar in the right-sized space (for example, not ‘Mariesii’ among the doublefiles, shown, but ‘Watanabei’ if you only had a smallish area). Even the lightest form of pruning, the removal of spent flowers called deadheading, isn’t needed with most viburnums, since what you want is fruit after the flowers (unlike all that deadheading with lilacs, for instance, to prevent messiness).


POOR PLANNING TO BLAME

Most of the pruning I’ve had to do on viburnums was because I didn’t leave enough room for the plant to reach its eventual size, and poor planning (meaning my impatience to have a filled-in garden) caught up with me in time. I have cut several viburnums to the ground or thereabouts in very early spring, when they simply got too big for where I had placed them, and let them re-grow. My list of successful such butcher jobs includes the European cranberrybush (V. opulus) and its American counterpart, V. trilobum, and various leatherleaf viburnums (V. rhytidophylloides and rhytidophyllum). Some have had this treatment twice already in their lives with me. Poor dears.

But if all I really need is a little fine-tuning or gentle re-shaping, which is the norm, I time my cuts right after bloom. That gives the plants time to regrow and potentially set blooms, even, for the following year (depending on how far down I cut on which kind). Except dead, damaged or diseased wood removal, I do not prune anything hard late in the season anyway, viburnums or otherwise, letting the new shoots from spring pruning harden off and prepare themselves for winter (then letting winter first do its thing, which can sometimes be the catalyst for pruning if ice or heavy snow load snaps twigs).

Generally speaking, you are not shearing the plant but cutting back judiciously to just above a node with each clip of the shears so the plant can make new shoots in a somewhat natural-looking style. Of course always look for suspiciously vertical new shoots that jut from the base—stems that look unlike the rest of the plant, and like they couldn’t ever fit in. Remove those as they develop, which I find that they do once a doublefile or leatherleaf viburnum, in particular, gets to a certain size. Also watch for any vertical (again, suspicious-looking) water sprouts off the main branches, which I have had from time to time, more on V. sieboldii than others I think. See my basic pruning tips for a primer on this kind of stuff.

Again, easy does it.

“Viburnum pruning should be an exercise in restraint,” writes Michael Dirr, the famed professor of horticulture from the University of Georgia whose “Manual of Woody Landscape Plants” is the standard reference. Those with a particular interest in what I think of as the finest genus of shrubs (read why I say that) may want to Dirr’s recent book, “Viburnums: Flowering Shrubs for Every Season.” Hopefully, he’d forgive me treating the occasional member of the genus as a cutback shrub after goofing with my garden designs, just like the viburnums did. Mea culpa.

53 comments
June 3, 2008

comments

  1. Kimbo says

    Hi, I want to plant Viburnum Odoratissimum (Emerald Jewel) around my swimming pool to act as a privacy hedge. I will keep the height of the viburnums approx. 2 metres high. They will be against a fence. My question is how well will they grow if I keep them to a 1 metre width. I don’t want them to take up too much room and grow too wide therefore leaving less room around my pool. Thanks

    • says

      I have never grown it, Kimbo (not hardy here — it’s Zone 8 and I am Zone 5), but the Floridata site says you can shear it into a narrow hedge — how narrow, I don’t know. I would think you’d lose the flowers in keeping it that tight, or have to wait till after flowering to cut it back hard each year (and probably a couple of more times, since it wants to be a big plant). Sorry not to have more detail for you.

  2. moira says

    Hi, I live in CT and have two huge viburnums in my yard about 15 x 15 feet …they get a fair amount of sun. They are probably 25+ years old and have gotten very leggy. We have never pruned them but in the past few years they have lost their lushness. This year it was very warm in the NE so though it’s the end of april, everything is in bloom. How should I prune these shrubs and is it too late in the season? Help! we love these bushes and they have been consistently blooming and smelling great for years so we got very lazy. Thanks.

    • says

      Moira, I am thinking because you mention fragrance that they are Viburnum carlesii maybe? Or burkwoodii? Are they more tree-like or shrubby/bushy in structure?

  3. Wilbur Siegrist says

    Ihave a Mariesii that is 5 yrs. Bloomed niece each year. Never pruned. This year the one side is beautiful and the other side has no blooms and leaves are only half the size. I am in zone 6 and we had very warm March and the heavy frosts then in April. Could this be the cause? Any advice? Thanks

    • says

      Hi, Wilbur. In my recent experience, the doublefiles are becoming more and more prone to dieback from this canker. After many, many years with them, I suddenly lost several. They are also prone to various other issues (find the links in the right sidebar of this Illinois Extension factsheet). Sounds to me as if that portion of the shrub is weakened by something. It bears closer inspection of the branch’s wood, the trunk, etc. for signs of other clues, I think.

  4. Margo says

    Three times I have had to move viburnums for lack of space. You have to plant the correct variety and give them space. I love the Shasta’s but have had great luck w native simple viburnum trilobum near the coast of ri

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