One of the questions I receive at the Extension Office this time of year is, “When is it time to cut back my roses for winter?”
Many of the modern and the old-fashioned shrubs or the climbing roses are quite hardy and do not need extra winter protection here in our region. Knock Out® roses also don’t need specialized winter protection.
Hybrid tea and grandiflora roses may be injured during severe central Kentucky winters or during fluctuations in temperature. When selecting roses for your landscape, always choose those that are able to tolerate the coldest temperatures in our area based on USDA hardiness zone maps. Frankfort is in Zone 6.
There are many methods to provide winter protection for roses. The whole idea of winter protection is to keep the plant uniformly cold and frozen all winter and prevent the damaging effects of alternate freezing and thawing.
Whatever method is chosen, don’t begin covering plants too early. Wait until a hard killing frost has caused most of the leaves to fall off of your roses. The microclimate where your roses are located is different than other‘s locations. You may also want to wait until the temperature has dropped into the teens for several nights.
The first step to protect roses for the winter is to be sure they go completely dormant. To accomplish this, stop fertilizing early enough so growth slows down. No fertilizer should have been applied after Aug. 15. To further encourage dormancy, stop deadheading or cutting flowers and allow the plant to form hips.
Before covering your roses at the end of the season, be sure to rake up and discard old leaves and other plant debris. Many disease-causing organisms overwinter in this material if left around the base of the bushes. Be sure to remove any damaged or diseased canes before winterizing.
Canes (or stems) may be pruned back to about 18 inches tall to make mounding easier. However, do not heavily prune your rose bushes at this time. Tying canes together to prevent wind whipping can also be done if you are in a particularly windy location or the canes are very thin.
MULCHING IS GOOD
Mulching is a good start for rose protection to moderate temperature extremes. The best form of winter protection for garden roses is to mound the base of each plant with compost or bark mulch that drains well. The mound of mulch should be 12 to 18 inches high.
Don’t use leaves, grass clippings, manure, or other materials that would remain wet since these can promote disease. Wet and cold is far more damaging than dry and cold. If these materials are composted and become a crumbly mix, they are appropriate winter coverings.
Soil can be used. Soil that is used to mound around plants should be brought in from outside the rose garden area. Scraping up soil from around the plant can cause root injury and lessen the plant’s chance for survival. After the soil mound has frozen, the mound can be covered with evergreen boughs, hardwood leaves, or straw to help insulate and keep the soil frozen.
A variation of the mounding method that may offer a bit more protection is one utilizing collars. An 18-inch-high circle of hardware cloth or chicken wire is placed around the plant. The collar is filled with compost, mulch or soil, allowed to freeze and then top mulched with straw. The benefit of the collar is that it holds the material in place all winter and prevents it from being washed or eroded away.
‘TUCKING IN' CLIMBERS
Less hardy types of climbing and rambler roses offer challenges with regard to winter protection. For marginal varieties, climbers may need to be removed from their supports and bent to the ground, then covered with six inches of soil and mulched. When laying climbers on the ground for covering, one needs to be very careful not to injure or crack the stems.
As the weather gets colder their long stems are not as pliable, and they are easily cracked resulting in the loss of that cane. Another method that can be used is to physically pack straw around the canes while they are still attached to the trellis or support. The straw is held in place with twine to keep it in place over the winter.
Finally, always remember that healthy roses are much more likely to make it through severe winters than are roses weakened by disease, drought, insects, or nutrient deficiencies. Also, the decisions that are made when preparing the site for roses really governs what kind of success you will have in winter survival.
A rose that is planted in poorly drained soil will suffer and often not survive the winter when that same rose, planted in a well-drained site, will flourish. Healthy plants that have been appropriately cared for have a much better chance of making it through a long, cold winter.
Mounds should be carefully removed in the spring after danger of frost is past. Don’t be too anxious because new tender shoots can be injured by a light freeze. Keep some straw or mulching material handy to cover plants in case of late frost.
For more information, log on to http://www.ca.uky.edu/agc/pubs/id/id118/id118.pdf or call the Extension Office and ask for information on winterizing roses. The Extension Office can be reached at 695-9035, or email DL_CES_Franklin@email.uky.edu.