Hi, Well it depends on what kind of roses you have. If you are growing tough, shrub roses, they can be left alone or with just a light mulch of shredded bark or leaves. If you have more tender types such as hybrid teas, floribundas, and grandifloras, I would mulch them with some additional soil around their bases. The key here is that if your nightly temperatures regularly stay in the 20's or below, then your roses need to be protected. And, with these types of roses, your goal is to protect the graft of the rose (the swollen part of the stem at surface level). And, the best way to do this is to mound soil up around the plant to a depth of about 12 inches to protect that graft. In the early spring, after nightly temperatures stay above freezing, you can gently remove that extra soil and use it someplace else in the ground. Do not hoe up soil from around your roses because you can damage the plants' shallow root systems. Bring in fresh soil for winter protection.