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Garden Obstacles: Pruning

Updated: Jan 31

Even though we are gardening with native plants, sometimes pruning is necessary for their health or to control their size, especially in a residential setting. A simple rule of thumb: If it blooms in the spring, prune it immediately after flowering; if it blooms in the summer, prune it in the winter or early spring. Of course, there are plenty of exceptions to this rule.


What is Pruning and Why Prune?


Pruning is the selective removal of specific parts of a plant for the benefit of the plant. Pruning to maintain health and aesthetics may include removing dead, injured, or diseased parts.


Since we are discussing native trees/shrubs and perennials, we only need to prune when necessary. This would include overgrowing its space or being kept as a hedge. When pruning, we want to accentuate the natural features of the plant.


Some quick pruning lessons:

  • Broken or dead branches are not an issue when gardening for habitat and wildlife. Unless, of course, the broken or dead branches are a danger to a building or people.

  • Heavy bleeders like Acer (Maple), Betula (Birch), and Juglans (walnut) should not be pruned until summer or fall and only if necessary.

  • Never top a tree. This means never to cut the leader. Topping is only good for shrubs being grown as hedges.


Needled Evergreen Pruning:

  • Some of our native evergreens do not resprout new growth like some non-native conifers. For example, Taxus (yew) and Cryptomeria (Japanese cedar) have latent buds and will put forth new growth. Our native Juniperus virginiana (Eastern red cedar), Thuja occidentalis (American arborvitae), and Chamaecyparis thyoides (Atlantic white cedar) do not tolerate backcutting (cutting past the new growth into the old growth). If you must prune these trees, do so before the new growth emerges, or only prune within the needled portion of the tree.

  • Pinus strobus (Eastern white pine) may be controlled by cutting the new candles in the spring by half. This will make a fuller tree.


Deciduous (not evergreen) Pruning:

  • Never shear a shrub unless its intended use is as a hedge.

  • Overgrown, older shrubs may be cut back to the crown within 6-10" of the ground.* This will require another pruning in the summer (July) removing half or more of the new canes. Note: prune back to outward-facing buds. If you do not do this, the inner portion of the plant will become overly dense. An example are Viburnum dentatum (arrowwood) and Salix discolor (pussy willow). They are much happier shrubs if they get a rejuvenation pruning every 3 years or so. Pussy willows grow 4-6' or sometimes more per season, so don't be afraid to cut them immediately after they are done flowering. Of course, if you want a tree-form pussy willow, do not do this pruning method.

  • A kinder approach to older shrubs is to remove 1/2 of the branches down to the base. Remove the oldest stems, inward (facing) branches, and anything that takes away from the aesthetic of its natural form. Many of our native shrubs sucker and this is what we want them to do for wildlife habitat. For example, Aronia arbutifolia (red chokeberry) suckers to form a colony. For better fruiting, it is best to cut out the oldest stems. Remember it blooms in the spring so pruning should be done immediately after it flowers. if you are looking to control the height or to force it to fill out a bit more as it can be a bit leggy. Or you can let it behave naturally and never prune it.

  • An easier method is to remove 1/4 to 1/3 of the oldest branches over a 3-4 year period. This method takes longer but it allows the shrub to still look attractive during the process.


Broad-leaved Evergreens:

  • Ilex opaca (American holly) is very tolerant of pruning and will regenerate new limbs even if cut to the ground. I don't recommend pruning our hollies, because it will take away from their natural pyramidal shape. Of course, remove diseased or dead wood. You can lightly 'top' a native holly to have a shorter/fuller tree but that is a lesson for another day.

  • Rhododendron maximum (Great Rosebay) requires very little pruning. If necessary, prune immediately after flowering so you don't lose any of next year's flowers. Dead or diseased branches may be removed at any time. They may also be cut down to the crown in late winter or early spring, as noted above in deciduous pruning. It will be several years before the plant fully recovers. If you want to be less dramatic, you may also cut the stems to varying heights of 2-4' tall.*


Native Hydrangea:

  • Hydrangea quercifolia (oakleaf hydrangea): prune only in the summer immediately after the flowers fade because they bloom on old wood.

  • Hydrangea arborescens (smooth hydrangea): prune down to 12" tall in early March because they bloom on new wood.


Cornus sericea (red twig dogwood)

  • It is not a low-maintenance shrub. You must prune out old stems in the winter (Feb-mid March) or cut back the entire plant to rejuvenate it. As long as you prune it before bud break you will be fine. Many freak out of this, but if you want gorgeous red stems the following winter, you must prune them. Red twig dogwood can grow 3-6' per year depending on how happy it is.

Pruning Native Vines:

  • Clematis virginiana (woodbine): prune at any time during the growing season to maintain the shape and have a fuller plant. It does bloom on new wood so prune in late fall to early spring.

  • Lonicera sempervirens (coral honeysuckle): I cut mine back usually in late winter. It can be trimmed at any time during the season but right after its first flush of flowers is best so the rebloom will not be affected. Mine blooms through December.


Small Shrubs Acting as Perennials:

  • Callicarpa americana (American beautyberry): technically a woody shrub but it can be cut back to 6-18" from the ground every spring because it blooms on new wood.

  • Hypericum prolificum (shrubby St. John's wort): same pruning method as above.


Summer (long-day) and Fall Blooming (short-day) Perennials:

  • Summer blooming perennials (June-August) may be cut back no later than mid-May. I let mine get to be about 12" tall and then cut them by 1/2. They may bloom a little later in season but you will be rewarded with more flowers and this means more pollinators. Examples of summer bloomers are Phlox paniculata (garden phlox), Monarda species (bee balm, bergamot, etc.), Heliopsis helianthoides (false sunflower), and Helianthus species (woodland, swamp, and thin-leaved)

  • Fall blooming perennials (September-November) may be cut back by 1/2 to 2/3 from the ground no later than July 15. Doing this will produce a tidier and more floriferous plant that blooms when it's supposed to. Again, more flowers, more pollinators! Examples of fall bloomers are Aster species, Vernonia (ironweed), and Physostegia virginiana (obedient plant).

The most important rule is choosing the right plant for the right place. If you do this, maintenance will be kept to a minimum.


Photos (KMS Native Plants): First Row: Salix discolor (pussy willow), Pinus strobus (Eastern white pine), Ilex opaca (American holly); Second Row: Fagus sylvatica (European beech) pruned a hedge the same way the native beech would be pruned, Clematis virginiana (woodbine), Lonicera sempervirens (coral honeysuckle); Third Row: Viburnum dentatum (arrowwood) berries, Hydrangea quercifolia 'Ruby Slippers' (oakleaf hydrangea cultivar), Callicarpa americana (American beautyberry); Bottom Row: Hypericum prolificum (shrubby St. John's wort), Vernonia noveboracensis (NY ironweed), Heliopsis helianthoides (false sunflower.


For illustrations on the above-mentioned pruning styles, please click on the link below in the references.


I hope this helps you with some of your pruning questions. As usual, f you have any questions, please feel free to contact me at kmsnativeplants@gmail.com.


*If the hard-cut rejuvenation method is the option you choose, the plant will need a bit of TLC including mulching, extra watering, and some rich compost. This goes for all rejuvenation pruning.


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References:

  1. An Illustrated Guide to Pruning Ornamental Trees and Shrubs https://ecommons.cornell.edu/handle/1813/3573




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