Prepare roses in late fall for best results
Back in late fall, after a hard frost, you should have raked up any dead leaves and removed any leaves from the bush. This prevents you from spreading diseases, like black spot. Then, you should mulch around the base of your bushes and up over the bud union. In locations where it gets windy, you can either wind prune, which amounts to pruning rose bushes to about 18 inches high, or you can tie your canes together to keep them from knocking about in the wind. The main goal in winter is to keep the rose bushes from undergoing multiple freeze-and-thaw events. It’s better for the bush to be completely frozen throughout the winter, than for it to freeze then thaw during one of those balmy February days, then freeze again.
Spring or winter pruning
Additionally, in winter or in spring, depending on where you live, and how busy you are, you can perform a more serious spring pruning. This activity consists of pruning the bushes down to around 8 to 12 inches tall (unless you have climbers or ramblers, which can be left longer), clearing out dead canes and diseased or dying shoots. This is also a good time to remove branches that cross other branches, have developed into unattractive or obstructive shapes, or appear to be root stock suckers.
Even though we call it spring pruning, we like to perform this task before spring buds start to appear. For one thing, it’s much easier to see what you’re doing. For another, pruning before budding gives you a chance to do some shaping, if necessary. Again, when you perform this task depends much on your location and the weather, as well as your schedule. Roses are extremely forgiving.
In some extreme locations, gardeners may mulch on top of the rose bush completely, up to several feet over the top of the bush. Some people use burlap sacks or straw, and then load compost or other mulch on top of that. Any mulching you can do will help protect the bushes from the freeze and thaw cycle. The University of Illinois has an excellent article on winterizing your roses.
Use the right kinds of mulch
Use what you have on hand for mulching, but if you use leaves, keep in mind the various considerations for different types of leaves. Remember that decomposing leaves will actually draw nitrogen from the soil. As a consequence, in spring, after you clear away any leafy mulch from your bushes, you may need a reasonably good dose of nitrogen fertilizer around the base of each bush to make up for any loss over winter. Not a high dose, but just a fertilizer you might use on your lawn, for instance.
Certain leaves can be problematic
Also, leaves of certain trees, such as walnut trees, are not good for mulch. Additionally, fresh mulch you may get from tree trimmers, especially hemlock mulch, while not poisonous (Socrates drank his final tea from a different type of hemlock), freshly chopped mulch can heat up and pull nutrients from the soil.
Cages can be handy
According to numerous articles online, you can also use more hardware-based means to protect your bushes. You can cover the entire bush in mulch, then wrap chicken wire or gopher cloth around the mound. This also lets you add more mulch on top, and protects your mulch from washing away in any rains, or getting disturbed by animals.
Mulch according to the climate
Of course, if you grow roses in more temperate climates, say in San Diego or Phoenix, you may get away without mulching your roses over winter, and simply make sure you prune properly. In any case, basic mulching is always a good idea, and in drier climates, it can help keep the ground from drying out too much.
Some varieties fare better than others
According to some experienced Rosarians, old varieties on their own stocks often fare better in winter than do more modern hybridized roses, grafted onto root stock. Whenever there is a bud union, there is a risk of freezing and cracking at the union. Varieties like the rugosas have thrived in numerous locations from the Middle East to Northern England for perhaps thousands of years. As such, they have evolved to withstand some extreme weather.
Climbers, ramblers, and trees, oh my
In extreme weather conditions, meaning snow and ice, you may need to take extra precautions with your climbers, ramblers, and rose trees. Jackson and Perkins recommends covering the base of all three types of rose bush with a substantial amount of mulch–at least a foot to two feet over and around the base and bud union. For climbers and ramblers, tie the canes together, and if you get really wicked winters, wrap the canes in burlap, tying them to keep them covered, and move the wrapped canes down onto the ground, when possible. For rose trees, dig out some of the mulch and soil on one side of the tree, then gently bend the tree down to the down, covering it with burlap and mulch.
Take your chances
For most casual rose growers, this may be more work than you are willing to undertake. In that case, just make sure you mulch over the base of your bushes, covering the bud union, and hope for the best. In the worst case, you may lose the bush. But, it’s likely that the bush will survive and you may get off with a bit more pruning to do in spring. Roses are incredibly hardy plants and will survive a lot of extreme weather. However, if you have a rose that has sentimental value: your grandmother planted it, for instance, you may want to consider taking the extra precautions to protect the rose bush against the ravages of winter storms.