Here in Minnesota, you must protect roses not only against low winter temperatures, but also against fluctuating temperatures, particularly in spring.
The first step in avoiding winter injury is to keep your roses healthy during the growing season. Roses that have been fertilized and sprayed for insects and diseases are more likely to escape winter injury. Plants that have lost their leaves early in the fall because of disease or nutrient deficiencies are more susceptible.
Fertilize a final time in mid-August, using 0-20-20. Use no nitrogen to avoid encouraging new growth when the plants should be slowing down for winter. Protect all but the hardy roses by mounding or tipping them in mid-October. Mounding is easier, but tipping allows you to save more of the plant from year to year.
To mound roses, cut them back to eight to twelve inches. Cover them completely with soil. Cover each mound with a couple feet of leaves or straw. A chicken-wire cylinder will keep leaves and straw from blowing off.
To tip roses, tie the canes together. Then dig a trench out from the base of each plant. Loosen soil around the roots with a garden fork, and tip each rose into its trench. Use the soil you removed to cover the trenches. Then add leaves or straw, just like mounding. Finish by covering with chicken wire to hold everything in place.
In April, begin to uncover mounded or tipped roses by removing the leaves or straw as they thaw. In two to three weeks, roses should be completely uncovered and lifted upright. Water them well and trim off dead or damaged wood. You're on your way to a new growing season of beautiful flowers.
For more information contact your county office Extension Service Master Gardeners.
© 2011 Regents of the University of Minnesota. All rights reserved.
The University of Minnesota is an equal opportunity educator and employer.