I live in West Toronto. I used rose collars and mulch to protect my roses last Fall. The soil is sandy and I can dig in a spade depth near the roses. When should I remove the mulch?
Rose collars can generally be taken off once the soil thaws and the ground is workable without danger of causing compaction. Sandy soils have the advantage of good drainage, and therefore warm up and drain faster in the spring, than clay soils. However, pay attention to the weather forecast to avoid sudden changes of environment, especially low night time temperatures, as this may be harmful to your rose if you have removed the mulch.
I have added the following link from Landscape Ontario for future reference: http://landscapeontario.com/rose-care-throughout-the-year