Preparing roses for winter
Any discussion of how to help roses survive the vagaries of winter is sure to initiate a lot of different opinions ranging from “do nothing” to “bury plants completely” or “it can’t be done!” Personally, I believe many roses — namely shrub roses — can survive in cold climates with a little winter protection.
Roses can be killed or injured during winter in several ways: direct injury to tops or roots from extreme cold; rapid temperature changes; root injury from dry-out as a result of plants being heaved by alternate freezing and thawing; injury caused by mice under snow; and snow or ice breakage.
Injury from extreme cold can be avoided only by selecting hardy varieties. As a rule, roses with small blossoms tend to be hardier than the largest flowering types. Most hybrid tea varieties are less hardy than the grandifloras or floribundas. In addition, some climbing roses and many old-fashioned bush varieties tend to be hardy as are some series such as “Explorer” out of Canada. Hardiness depends on variety and type. However, this is based more on observation than actual hardiness studies, so gardeners must be willing to take chances an experiment with different varieties. But the good news is that proper winter protection can help plants survive.
For bush varieties, start by mounding soil 10 to 12 inches around the base of the plants. Then add another 12 to 16 inches of mulching material such as leaf mold, straw, hay, or pine needles over the mound to help stabilize soil temperatures. This extra protection means less freezing, thawing, and subsequent heaving. If you have many rodents around, you may want to skip the mulch materials as they provide a winter home for unwanted wildlife. Ideally, mounding should be applied in mid to late November. Earlier application may slow development of stem maturity and hardiness.
You may need to prune the canes back to the surface of the mulch for ease of covering, but don’t cut back any further. Wait until spring, so you can see which canes or parts of canes have died, then cut them back. If the winter is mild, or your mulching thick, you may have to cut back very little.
Climbing roses survive the winter best when you remove the canes from the fence or trellis and fasten them to the ground. Snow cover will protect them from extremely low temperatures. Where snow cover is undependable, mound snow or mulch over the canes on the ground. Remove the mulch as plants start to grow. Earlier removal may cause the rose stems to dry out. The common practice of wrapping stems and trellises with straw and paper or burlap provides, at most, a few degrees of protection on cold nights. It is less dependable than protecting stems with soil on the ground. You can also make a frame to catch snow if snow cover is reliable in your area.
Remember, these precautions will not always ensure survival and prevent injury. However, they usually will enable northern gardeners to grow some of the less hardy roses.
Dr. Leonard Perry is Extension Professor, Department of Plant and Soil Science at the University of Vermont. Visit his website at http://www.uvm.edu/~pass/perry/index.html