Overwintering tree form knockout roses
In zone 5b do I need to treat knockout tree roses the same as a regular tree rose? Meaning oil spray and covering root and graft?
Cook County Illinois
I would agree with that. I normally recommend using dormant oil in late winter, before growth begins, but I can't see a major problem with using it according to label directions after the foliage has dropped off.
Bring in some mulch to cover the lower trunk up passed the graft union. If another "polar vortex" is predicted, you can heap more mulch and leaves over the bush to give it some extra protection, but that shouldn't be necessary for a normal winter.