When shrubs outgrow their space, get gangly in old age, lose aesthetic value from repeated pest attacks or environmental responses or otherwise detract from the landscape, gardeners may wish to renew, rejuvenate or remove them.
Shrub renewal refers to the process of selectively removing old or unhealthy stems and canes at ground level, leaving only young, healthy stems or canes. Lilacs are an example of a species of shrub that responds well to renewal pruning. Older lilac canes are often infested with ash lilac borer and are less vigorous than newer canes. Removing old canes allows the root system to put more energy into younger shoots and results in an overall healthier plant.
Renewal pruning also results in larger, more abundant blooms in most cases.
For most shrubs, renewal pruning should be done when plants are dormant in late fall, winter or very early spring. Early spring-flowering shrubs like lilac and forsythia can be pruned as soon as they finish blooming in midspring.
Shrubs that respond well to renewal pruning in addition to lilac are chokeberry, coralberry, upright cotoneaster, multi-stemmed dogwoods, elderberry, forsythia, honeysuckle, many hydrangeas, mockorange, privet, quince, shrub roses, bridalwreath (Van Houtte) spirea, weigela and others.
Some gardeners may choose to do a little renewal pruning each year, some may prune three to four years in a row then take three to four years off, and others may remove several canes at a time once, then wait several years to prune again. Do what makes you feel comfortable to get the plant healthy again in a time frame that works for you.
Shrub rejuvenation refers to the process of cutting the entire plant back to ground level. Rejuvenation offers the same benefits of renewal and is a quick one-shot method at refreshing an old overgrown or gangly shrub, but only works on some species.
Rejuvenation pruning should be done in early spring just before bud break. Cutting back shrubs to the ground in summer through fall will kill even some of the hardiest species.
Lilacs can be pruned through the rejuvenation method for a quicker refreshment than renewal pruning provides. Other shrubs that respond well to rejuvenation pruning are coralberry, multi-stemmed dogwoods, forsythia, honeysuckle, Annabelle hydrangea, mockorange, privet, weigela and others.
A few shrubs, including quince, will rejuvenate when pruned all the way to the ground, but will completely lose their shape and end up bigger and ganglier than they were to start. Always check on individual species before pruning with the rejuvenation method.
Removing a shrub is often an extensive task. Decide first if you can get by only removing the above-ground part or if you really need the entire plant out of the site.
If roots can be left intact, cut the entire plant back to the ground. This can be done any time of year, but you will likely see fewer sprouts coming back from the roots if the plant is cut back in mid- to late-summer. Other options to reduce the number of returning sprouts are to cover the area with black plastic for a few weeks immediately after cutting the plant back, or treat cut stems individually with stump killer of your choice. Read and follow all label directions if using a chemical.
Home remedies to kill plants and stumps such as salt, bleach, vinegar, gasoline and others should never be used. They are mostly ineffective and instead kill beneficial microorganisms in the soil. They can also leach into waterways.
If the roots have to go too, call Kansas One Call (Dig Safe) first to determine if underground utilities might be tied up in the roots. When the area is marked clear, cut the shrub down to ground level and grind out the roots with a stump grinder. A landscaper or arborist can do the grinding or you can rent a grinder from a rental supply store.
The final options for removing the shrub and its roots are pulling and digging. Both are labor intensive. Be careful to think about anything else in the way or that might be affected. A lot of shovels and spirits get broken trying to dig out shrubs.
The Kansas One Call number is 811, or you can register on its website, kansasonecall.com.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.