Roses

Q&A: When Should I Prune Shrub Roses?

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Shrub rose pruned back in early March. Photo: M. Talabac

Q:  When do I prune shrub roses? Is now okay? How far back do I cut?

A:  Although you probably won’t kill a plant by doing it now (November) it’s best to wait until late winter or early spring (late February to early March time frame for central Maryland). Pruning before the dormant season might reduce some winter hardiness, potentially contributing to stem dieback. If you pruned in fall and a drastic cold snap were to cause plant tissue damage during the winter, then the second trimming to remove the dead wood would shorten the stem even more, as opposed to delaying trimming until the worst of winter is past and only making one trim at the height you prefer.

The height to reduce the stems depends on personal preference, and recommendations vary, but one convention is to cut shrub rose stems down to about 15 or 18 inches off the ground, though you could go lower to 12 inches or higher to 24 inches. Roses bloom on new growth (except for many climbing roses that also flower on old growth), so pruning at the end of winter will not remove flower buds. If you delay pruning into April or so, though, you might postpone when those first flowers of the season appear.

If a rose is so rangy that it’s just in the way, like arching over a sidewalk or blocking a hose spigot, you can compromise and make a light trim now to tidy it up so the thorns don’t catch people and then do the main pruning in several months.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.

What’s Eating My Rose Leaves?

Maryland Grows1 Comment
roseslug sawfly damage on rose
Roseslug sawfly damage on rose. Photo: UME/Ask an Expert

Q: My rose leaves have white spots and holes in them. What causes this and how do I treat it? Is there a natural remedy that does not involve powerful chemicals?

Answer: It looks like your rose has symptoms of sawfly damage. Check the undersides of the leaves and look for tiny green larvae that look like little worms or caterpillars. These are the juvenile stage of an insect called roseslug sawfly.

Roseslug sawflies are neither slugs nor flies. They belong to the same order of insects as wasps, bees, and ants (Hymenoptera). Adult female sawflies use their unique ovipositor (egg-laying part) to saw a small slit in a leaf or stem where they lay their eggs. When the eggs hatch, the larvae feed on the leaf surfaces and cause an etched or scratched appearance. Some roseslug larvae chew through the leaves entirely. Damaged foliage turns brown and curls up as the season progresses.

bristly roseslug on rose leaf
Bristly roseslug (Cladius difformis). Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
bristly roseslug sawfly adult
Bristly roseslug (Cladius difformis), adult stage. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

In Maryland, there are three species of roseslug sawflies that cause damage to roses: the bristly roseslug sawfly, the roseslug sawfly, and the curled rose sawfly. Most of the feeding activity on roses in Maryland is seen in May and June, but some sawfly larvae can continue to be active until fall. Other insects, such as Japanese beetles, also cause chewing damage on rose foliage (typically in June-July).

rose-brown-leaves
Browning and leaf curling from rose slug sawfly damage. Photo: UME/ Ask an Expert

The best way to manage roseslug sawflies without chemicals is to monitor your plant(s) for damage symptoms early in the season (start looking in May) and manually remove any larvae (squish them or pick them off and discard them). A forceful spray of water from a garden hose targeted toward the leaf undersides can also get them off. Once dislodged, they cannot climb back up into the plant. Horticultural oil and Spinosad also work well against sawflies. Read and follow the product label instructions for the correct application procedures.

Two sawfly larvae are present on the undersides of rose leaves. Photo: C. Carignan

Predatory insects and birds help to manage sawfly populations naturally. Adding more flowering plant diversity to your landscape will provide food and habitat for beneficial animals that in turn help to reduce future pest problems.

Rose shrubs usually recover from sawfly damage eventually, as long as they are not struggling from other ailments or stressors such as drought.

Additional Resources

Sawflies | UME Home & Garden Information Center

Rosie Defoliators | Bug of the Week, University of Maryland, Department of Entomology

By Christa Carignan, Maryland Certified Professional Horticulturist, Coordinator, University of Maryland Extension Home & Garden Information Center. Read more by Christa.

Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask Extension.