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 late winter or early spring. Remember to properly clean your tools, as diseases may be moved from plant to plant.
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:
The most important rule is choosing the right plant for the right place.
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. These can be removed at any time.
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 (cutting the leader). Topping is only good for shrubs grown as hedges.
Never shear a deciduous (not evergreen) shrub unless its intended use is as a hedge.
Prune back to outward-facing buds. If you do not do this, the inner portion of the plant will become overly dense.
Deciduous (not evergreen) Pruning:
Overgrown shrubs may be cut back to the crown within 6-12" of the ground immediately after they are done flowering.* Viburnum dentatum (arrowwood), Salix discolor (pussy willow), and Cephalanthus occidentalis (buttonbush) should get a rejuvenation pruning every 3-5 years or so in the spring. Arrowwood grows 2’ per year and pussy willows grow 4-6' per year so don't be afraid to cut them. This style of pruning will require another pruning in the summer (July) removing half or more of the new canes to prevent crowding or rubbing branches.
Another option for older shrubs is to remove 1/2 of the branches down to the base. Remove the oldest stems, and inward (facing) branches.
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Cornus sericea (red twig dogwood) 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. If you want gorgeous red stems the following winter, you must prune them. Red twig dogwood can grow 3-6' per year.
Fruiting natives like Aronia arbutifolia (red chokeberry) and Vaccinium corymbosum (highbush blueberry) sucker to form colonies. For better fruiting, it is best to cut out the oldest canes. Sambucus canadensis (black elderberry) may be pruned to 2’ from the ground and remove any canes that are 2+ yrs old.
Small Shrubs Masquerading as Perennials:
Callicarpa americana (American beautyberry) and Hypericum prolificum (shrubby St. John's wort) are woody shrubs but they may be cut back to 6-18" from the ground in late winter/early spring as they bloom on new wood.
Photo (KMS Native Plants): C. americana berries in the fall
Needled Evergreen Pruning:
Juniperus virginiana (Eastern red cedar), Thuja occidentalis (American arborvitae), and Chamaecyparis thyoides(Atlantic white cedar) do not tolerate back cutting (cutting past the new growth into the old growth). If you must prune these trees, do so before the new growth emerges.
Pinus strobus (Eastern white pine) may be controlled by cutting the new candles in the spring by half. This will create a fuller tree.
Broad-leaved Evergreens:
Ilex opaca (American holly) does not require pruning but if you must prune, do it in the winter. Only remove diseased or dead wood. You may also thin out some of the upper branches, so the lower branches still receive light.
Rhododendron maximum (Great Rosebay) requires very little pruning. If necessary, prune immediately after flowering. 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 with a rejuvenation pruning. It will be several years before the plant fully recovers.*
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 12-18" tall in early March because they bloom on new wood.
Pruning Native Vines:
Clematis virginiana (woodbine): prune at any time during the growing season to maintain the shape and a fuller plant. It does bloom on new wood, so prune (cut back) in early spring.
Lonicera sempervirens (coral honeysuckle): cut back in late winter/early spring. It may be trimmed and shaped any time during the season but right after its first flush of flowers is best so the rebloom will not be affected.
Photo (KMS Native Plants): Late winter pruning of L. sempervirens (coral honeysuckle)
Summer (long-day) and Fall Blooming (short-day) Perennials:
Summer blooming perennials (June-August) may be cut back no later than mid-May. Cut them back by 1/3 to 1/2. They may bloom a little later in season, but you will be rewarded with more flowers and that means more pollinators. Examples of summer bloomers are Phlox paniculata (garden phlox), Monarda species (bee balm, bergamot, etc.), Eutrochium species (Joe Pye Weed), Pycnanthemum species (Mountain Mints), 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. Some say July 4th because it is easier to remember. 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 Solidago species (Goldenrod), Asters (Symphyotrichum, Doellingeria, Ionactis, Eurybia), Vernonia species (ironweed), Helenium autumnale (Sneezeweed), and Physostegia virginiana (obedient plant).
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. If you have any questions, please feel free to contact me at kmsnativeplants@gmail.com
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*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
2. Ingels, Jack E. Landscaping: Principles and Practices. Albany: Delmar Publishers, 1997
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