Hacking & Whacking - Dealing with Overgrown Shrubs
Posted: April 10, 2012
Shrubs are important components of residential and public landscapes. They are used to block views, create privacy, establish borders, and provide interesting foliage and flowers. Too often, shrubs are planted and then allowed to grow with little or no management. If pruned at all, they are typically subjected to periodic shearing. Eventually many shrubs grow too big for their site or for the plant structure itself. Now that winter is over, we see them everywhere we look: big, unruly, overgrown shrubs.
Rejuvenation pruning is the more severe of the two techniques, and not all species can tolerate it. Plants that are stressed or in poor health may not survive this severe level of pruning. In rejuvenation pruning, the shrub is pruned by cutting off all old branches at or near ground level. Healthy shrubs will respond by sending up multiple new shoots, and these will need to be thinned to reduce competition and maintain the natural form of the shrub. One benefit of rejuvenation pruning is its immediacy; when the job is done, that ugly overgrown shrub is literally gone. This is, of course, also a drawback since what is left behind is an unsightly stump, at least until new growth ensues.
Deciduous shrubs that can tolerate rejuvenation pruning include Tartarian and redstem dogwood, forsythia, rose of Sharon, hydrangea, privet, honeysuckle, elderberry, spirea, and lilac. Butterfly bush and Chastetree (Vitex) can be pruned annually in this manner once we are past danger of a hard frost. Callicarpa can be rejuvenated by pruning to 12 inches rather than cutting at ground level. Evergreen shrubs will not tolerate rejuvenation pruning.
Renewal pruning is a gentler approach to dealing with an overgrown shrub, but it is a process that takes several years. In renewal pruning, about one-third of older wood is removed each season over three years, primarily by using thinning cuts back to the crown or main stem. This approach maintains the overall shape of the shrub while reducing its volume and height over time. In response to this pruning, and as light is allowed to penetrate the canopy, many new shoots may be initiated. As in rejuvenation pruning, these new shoots will need to be thinned. Although renewal pruning takes longer to complete, the visual impact on the landscape is much less than rejuvenation pruning.
Many deciduous shrubs respond well to renewal pruning, including barberry, beautybush, cinquefoil, pyracantha, forsythia, honeysuckle, hydrangea, lilac, mockorange, privet (use a 4-year cycle), flowering quince, spirea, and weigela. Renewal pruning can also be used on some evergreen shrubs such as boxwood, cherry laurel, and rhododendron.
They say that an ounce of prevention is worth a pound of cure, and avoiding the problem of overgrown shrubs is easy to do. First and foremost, make sure to fit the plant to the site. Don’t force a shrub species to fit into a space that is too small for its natural growth pattern or vigor. Then maintain the proper size of shrubs using appropriate thinning and heading cuts as needed to manage shrub growth, size and health.
Information for this article was drawn from the Penn State Extension publication "Pruning Ornamental Plants," (PDF) prepared by James Selmer, Vincent Cotrone, Martin McGann, and Robert Nuss. More detailed information can be found in this publication.