I unsuccessfully grew it in zone 5.

I assume you are asking for someone else. It will be very helpful to give more information about where this person is. A western zone 4 is very different from an eastern one. It is more like an eastern zone 5.

Thank you both. I am moving next spring to a small town on the St. Croix River, north of Minneapolis. Alchymist is one of my favorites in my current zone 6 garden and I have considered digging it and taking it with me. As I recall it took a couple of years to get going, but now, after five years it is a very vigorous plant with many gorgeous blooms in the spring.

Madgallica - I'm curious to why you say a western z4 is more like an eastern z5?

I have had this rose for a couple years In zone 6a. It had winter kill almost to the ground in a spot facing the weather, so I moved it to a protected spot on its 2nd year. It grew well until vole damage, it’s still alive.

Because that is how the roses behave.

When I first started on rec.garden.roses, there were a lot more cold climate people, and we tended to grow a lot of the same roses. So it wasn't hard to compare how varieties performed differently in different climates. Roses that normally die back to the ground here, did much better further west in drier places with comparable winter temperatures. So my rule of thumb was that you picked up about half a zone between here and Illinois, and another half zone between Illinois and Colorado.

*Why* this is true has been puzzling me ever since. Part of it is probably that many plants prefer drier winters, and can handle more severe temperatures if kept dry. This is very common zone-pushing knowledge. Our comparatively short, cold summers may also play a part.

Thanks - I've never lived in the midwest or east. What you say makes sense.