Pruning Viburnum shrubs - Ask Extension
Dear Sirs/Madam:
I have attached a photo of some Viburnum shrubs that were planted 20 years ago. They are very large and need pruning. They are woo...
Knowledgebase
Pruning Viburnum shrubs #813855
Asked October 10, 2022, 5:49 PM EDT
Dear Sirs/Madam:
I have attached a photo of some Viburnum shrubs that were planted 20 years ago. They are very large and need pruning. They are woody in the center with limbs that appear dead, or have no leaves. When should I prune these and to what extent. Could you recommend a book on pruning as I have numerous plants, shrubs and trees that need pruning that I usually do at the wrong time. Thank you. Dan
Anne Arundel County Maryland
Expert Response
Hello Dan,
Although pruning is not required for the plant's health, if desired for aesthetics, you can reduce their size to some extent without causing the plants too much stress if you don't remove more than about a quarter (or at most maybe a third) of their current canopy size. While trimming more might be well-tolerated, it will delay the resumption of bloom and may make the shrubs more vulnerable to other stresses in the meantime while they regrow.
Viburnum is a diverse group with many species, so knowing which these are may inform when pruning is best. In general, those that bloom on old wood (that is, growth that formed the prior year) should be pruned after flowering if you want to avoid missing-out on blooms. If any bloom on new wood (growth produced the current year) then early-season trimming won't impact blooming much since buds develop later. In either situation, if you don't mind removing blooms for that year, then you can trim in early spring regardless of species. Don't prune these or any shrubs in autumn unless you're removing dead or damaged growth.
Leafless branches on the Viburnum could be caused by last year's cicada egg-laying damage, drought stress, a fungal Botryosphaeria infection, or other issues. While it's normal for interior wood to have few or no leaves due to the shade cast by the plant's own canopy, an entire branch that is leafless all the way out to its tips during the growing season may be dead or weak enough that it should be removed. How much of this older, inner wood that will leaf back out again after a more drastic pruning remains to be seen, even if it's exposed to more light as a result.
There is no one book that we'd recommend, but you can use Extension references like Virginia Tech's pruning guides (linked below, PDF files) as a starting point for many of the commonly-grown species: There's also the Principles of Pruning series by Iowa State University Extension geared towards pruning young trees. As a general guideline, if a shrub is spring-blooming, prune it just after bloom, and if it's summer-blooming or later, prune it in spring since flower buds would not have developed yet. Diseased wood can be removed at any time of year. Always have a good reason for trimming (especially for trees) since every cut carries the risk of wood decay entry before the wound can seal-over (don't paint or coat it with anything). If there are specific perennial, shrub, or tree species you want confirmation of a pruning time for, feel free to ask.
Miri
Although pruning is not required for the plant's health, if desired for aesthetics, you can reduce their size to some extent without causing the plants too much stress if you don't remove more than about a quarter (or at most maybe a third) of their current canopy size. While trimming more might be well-tolerated, it will delay the resumption of bloom and may make the shrubs more vulnerable to other stresses in the meantime while they regrow.
Viburnum is a diverse group with many species, so knowing which these are may inform when pruning is best. In general, those that bloom on old wood (that is, growth that formed the prior year) should be pruned after flowering if you want to avoid missing-out on blooms. If any bloom on new wood (growth produced the current year) then early-season trimming won't impact blooming much since buds develop later. In either situation, if you don't mind removing blooms for that year, then you can trim in early spring regardless of species. Don't prune these or any shrubs in autumn unless you're removing dead or damaged growth.
Leafless branches on the Viburnum could be caused by last year's cicada egg-laying damage, drought stress, a fungal Botryosphaeria infection, or other issues. While it's normal for interior wood to have few or no leaves due to the shade cast by the plant's own canopy, an entire branch that is leafless all the way out to its tips during the growing season may be dead or weak enough that it should be removed. How much of this older, inner wood that will leaf back out again after a more drastic pruning remains to be seen, even if it's exposed to more light as a result.
There is no one book that we'd recommend, but you can use Extension references like Virginia Tech's pruning guides (linked below, PDF files) as a starting point for many of the commonly-grown species: There's also the Principles of Pruning series by Iowa State University Extension geared towards pruning young trees. As a general guideline, if a shrub is spring-blooming, prune it just after bloom, and if it's summer-blooming or later, prune it in spring since flower buds would not have developed yet. Diseased wood can be removed at any time of year. Always have a good reason for trimming (especially for trees) since every cut carries the risk of wood decay entry before the wound can seal-over (don't paint or coat it with anything). If there are specific perennial, shrub, or tree species you want confirmation of a pruning time for, feel free to ask.
Miri
