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Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved
Roses are by all odds the most popular flowering shrub in America. They enjoy the same popularity in Utah and getting through the winter is sometimes a real challenge.
The best scenario for roses is to cool down gradually and stay cold but not too cold throughout the winter. Since no one can predict what winter is going to do, look at the how’s and where’s of rose care to help them survive the winter.
Winter damage on roses takes several forms. Low temperatures below 10 degrees will kill exposed canes on hybrid tea roses. Repeated freezing and thawing ruptures the plant cells and cause them to loose water and die. The freeze/thaw cycle is also damaging. When water freezes it expands, when it thaws it contracts. This heaves the plants out of the ground, severing the root system.
Strong winter winds also cause additional damage. It dries out or desiccates the canes. It is likely to break off the canes or sever the plant roots as they sway in the wind.
More rose injury occurs due to freezing, thawing, and heaving action throughout the winter than severe cold temperatures.
Snow is not harmful to roses; in fact, it helps insulate the soil and the plant from temperature extremes if it covers the plants. However if the plants collect too much snow on the canes, the weight might break off the canes.
The amount of winter protection your roses need depends on the kinds of roses and on your individual microclimate. Where winter temperatures regularly reach 10degrees F. or lower, all modern roses need some sort of winter protection. Hybrid teas, grandifloras, and to a lesser extent floribunda roses need protection. Old-fashioned roses, species roses and most shrub roses are hardy without winter protection. The best winter protection starts with healthy plants. Maintain healthy plants throughout the growing season by keeping them watered and pruned and by controlling insect s and diseases. If your roses have yellow leaves with dark green veins, treat them with an iron chelate. Chlorotic plants are far more likely to be winter killed than those that have healthy green leave throughout the growing season. The whole practice of winter protection is not to prevent the cold from reaching the plants, but to keep them cold. Now that leaves are frozen and the soil is frozen in many locations, it is time to winterize your plants. Start by cleaning up the area. Although you will delay the final pruning until next spring, remove any broken dead or diseased branches. Next, cut the candelabras off the tops of the canes. These are the spent blossom clusters. They will die over the winter and they are adept at collecting the snow and the also act as wind sails.
When you have finished, tie the canes together loosely with a string or piece of yarn. This helps prevent wind whipping and cane breakage. Wait until the soil freezes until you finish the final step of mulching in the plants. This step usually takes place in late November.