When do Small Trees Become Large Shrubs?
B
y midsummer, small trees and large shrubs grow upward, out, and bend over from the weight of leaves and fruits. Unfortunately, heavy, drooping branches invade sidewalks, patios, block views, and brush up against buildings and cars. Trimming back these stray branches in summer won’t harm them, although pruning woody plants is normally done in winter. Certain large species do this more than others, especially in the lush environment of a mulched and watered garden. These multi-
stemmed species (and their average unpruned mature heights) include buttonbush (Cephalanthus occidentalis 10–15), elderberry (Sambucus canadensis 8–10), indigo bush (Amorpha fruticosa 8–10), ninebark (Physocarpus opulifolius 8–10), Hercules’ club (Aralia spinosa 20–25), bladdernut (Staphylia trifolia 8–10), hazelnut (Corylus americana 8–10), smooth sumac (Rhus glabra 15–20) and winged sumac (Rhus copallina 10–12), arrowwood viburnum (Viburnum dentatum 6–8), smooth alder (Alnus serrulata 10–15), rough-leaved
SCOTT WOODBURY Horticulturist 18
July 2022 | kcgmag.com
dogwood (Cornus drummondii 15–20), and gray dogwood (Cornus racemosa 10–15). (If annually pruned, shrub heights will be about half these heights.) These are the species that have the potential to grow into small multi-stemmed trees if you let them go. The more shade they get, the taller and lankier they grow. This can be ideal if you want to see through them and enjoy the trunks and bark, because the mass of foliage is above the eye in this situation. You can further enhance this see-through effect by trimming
away the lower leaves and short side branchlets. But if your long-term goal is to keep these types of plants lower and shrubby, or create an eye-level screen, these are great native plant choices. To take advantage of their ability to screen, prune them every year or two. This should happen after plants are established (2 to 3 years), and involves removing 1/4 to 1/3 of the stems (the oldest) to the ground, every winter or two. This is a process called rejuvenation. It forces multi-stemmed woody plants to continuously gen-
Horticulturist Scott Woodbury is the Curator of the Whitmore Wildflower Garden at Shaw Nature Reserve in Gray Summit, Missouri, where he has worked with native plant propagation, design, and education for 30 years. He also is an advisor to the Missouri Prairie Foundation’s Grow Native! program. Find suppliers of native plants, seeds, and native plant services at www.grownative.org, Resource Guide.
