For rosarians in climates where winters are cold, October can be the saddest month. Chances are, you’ve already had the first frost and for the most part, the roses just aren’t very pretty anymore. Further, we’re leaving the flowers on the plants so they will form hips, helping the plants transition into dormancy. You may notice that the canes are starting to turn a purplish color, indicating that dormancy is starting.
Dormancy, of course, is a good thing. Virtually all roses are hardy perennials, so dormancy hardens off the plants so they can survive a cold winter. “Hardening off” in this context means that the plant parts are losing much of the water in their cells and the cell walls are thickening. Think about it; when water freezes, it crystallizes and those sharp ice crystals puncture cell walls. A cell with a punctured wall is a dead cell and lots of dead cells means a dead plant.
Mother Nature is smart and in cold climates, she transitions perennial plants into dormancy by allowing them to shed much of their turgidity when the days get shorter and the weather cools. Of course, the rosarian can screw it up royally by pruning at this time, which encourages the sap to run, or by applying winter protection materials too early, which keeps the plants warm, rather than allowing them to harden off. So, unless you want to cut an absolutely perfect flower, which is why you’re growing roses in the first place, leave the plants alone. They’ll harden off all by themselves.
As you may have noticed, some roses are hardier than others. Rose hardiness can include many different factors, but none of them is an absolute. The truth is that every variety of rose, whether it’s a climber, a hybrid tea, a floribunda, or a miniature, can be more or less hardy than another variety in the same category. Every winter is different as well. A rose you’ve always thought of as tender can come through a mild winter like a champ, or a really tough rose might die to the ground in a rough winter. That’s why Hardiness Zones are seldom assigned to roses. There are just too many variables.
Generally, however, own-root roses survive cold winters better than budded roses do. This is because own-root roses were propagated by cuttings, so they don’t have a bud union, that woody knob on the majority of rose plants. Most roses, however, are still propagated by budding, which is a form of grafting. The bud union is the point from which all the new canes will grow, so it’s important to protect that vital, vulnerable part of the plant. In cold climates, we plant the bud union a few inches below the level of the soil, so it’s protected from severe cold and wind.
Perhaps even more important, a rosebush that’s healthy going into fall has a much better chance of surviving winter than one that was devastated by disease all summer. Roses and other plants need their foliage to photosynthesize, so if the plant has been defoliated by one of the common and easily preventable rose diseases, it may not be strong enough to transition into dormancy and store enough energy to wake up again in the spring. It is best to keep roses disease free throughout the growing season.
Cold-climate rosarians should apply their winter protection materials between mid-November and Christmas, or six to eight weeks after the first frost in your Hardiness Zone. It’s important that you don’t do anything to your roses until they’re fully dormant.
So, if roses go dormant all by themselves in cold climates, why do they need winter protection? When I was a young rosarian, I tried to keep my roses warm over the winter. I wrapped them in everything from tar paper to carpet padding, and still I lost plants. One of my problems was poor drainage, which I’ve remedied now by raising my rosebeds, but my biggest downfall was in not realizing that I should have been trying to keep the plants consistently cold – not warm!
We have many sunny days throughout the winter, causing the surface of the soil to thaw and the exposed parts of the roses to warm up. Then the sun sets, and the temperature drops to well below freezing and it is these frequent thaw/freeze cycles that damage roses. The sap starts to run during the day and then it freezes at night, killing cells. The winter protection materials you apply keep the important plant parts from thawing during those warm days, allowing them to remain cold and dormant.
Ann Hooper is a certified American Rose Society Consulting Rosarian.