While tea roses and a few other types usually don’t survive in cold climates, many of the new series, as well as some of the older shrub rose cultivars (cultivated varieties), can survive cold winters with some protection. While these methods don’t guarantee that your rose plants will survive, they’ll surely help those that are marginally hardy.
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 drying out as a result of plants being heaved by alternate freezing and thawing; injury caused to stems by mice living under snow or in straw around plants; and snow or ice breakage.
Injury from the extreme cold can be avoided only by selecting hardy cultivars. As a very general guide, roses with small blossoms tend to be hardier than the largest flowering types. Most hybrid tea roses are less hardy than the grandifloras or floribundas. In addition, some climbing roses and many old-fashioned shrub cultivars tend to be hardy as are some series such as the Explorer roses that were originally bred in Canada.
Whether a rose survives, as with other perennials, depends in part on the microclimate”—the immediate area where it is planted. Adjacent to the warm south-facing wall of a building, or a slope facing north and exposed to winds, are all examples of microclimates. Even with a cold climate, or microclimate, proper winter protection can help plants to survive.
For shrub varieties, start by mounding soil or compost 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, or pine needles over the mound to help stabilize soil temperatures. This extra protection means less freezing, thawing, and subsequent heaving out of the soil. If you have many mice around, you may want to skip the mulch materials as they provide a winter home and ready food source in your rose stems. Ideally, mounding should be applied in mid to late November. Earlier application may slow development of stem maturity and hardiness.
If you have rabbits living in your landscape or nearby, you may want to surround your rose bush with a wire cage, especially if canes will be exposed and above the usual snow depth. Smaller mesh chicken wire usually is sufficient but can be chewed by a hungry rabbit. Heavier gauge rabbit fencing, or hardware cloth, provide better protection. You may want to install this first, then add your compost or soil within the cage frame.
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 is 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.
Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont