No garage?

Snuggle it up against the house. In 6b, a garage or unheated structure can get too warm, and the rose won't stay dormant. Too warm is worse than too cold.

If it gets below zero, you may want to bring it inside for a day or two. Other than that, it should be fine outside.

Don't prune it back until next spring.

I over winter about 30 pots in my backyard every year in Michigan zone 6b for the last 15 years. It is the south facing back wall of my house. I line them up along the wall, wrap them in burlap and bury them in leaves. Make sure there are leaves under them and all around each pot to the ground. This helps to insulate them. I do not put them in this winter storage until they go completely dormant. For me that is after Thanksgiving usually. Since they are outside and open to the elements I do not need to water them but if they are covered and can't get rain then they will need to be watered at least once a month all winter.

I heard you can bury the pot in ground and cover with mulch and dirt, the dig it up in spring. Sounds like a lot of work to me :)

Yes, you can sink the pot depending on the size and if you have a big enough spot to do so. I have done that with some small one gallon pots that I had my seedlings in. It is a lot of work both fall and spring and it is VERY important to carefully mark where the edges of the pot are buried. The first time I did this I didn't know to do that. In the spring I had no real idea of where each pot was and accidentally sunk my shovel directly into the center of one of the pots! The poor rose was a goner :( .

I agree with Seil. One year I put a pot against our house and lost it. I think the temperature fluctuation was the problem. Last year I left another pot out but covered with lots of oak leaves and it survived. We don’t have much leaves this year in our new yard so I plan to sink my pots in a trench then cover the top with soil. Our winter is not very wet but I heard mulch can cause rot and other problem so will try garden soil instead.

-Stacy

I’m a bit warmer, so this might not apply. I’ve had potted roses for more than a decade. I position them along a west wall that is well protected and that’s it. I've never lost one and only rarely get any dieback. I have done the chicken wire and leaf bit with a hydrangea but it’s a pain and really ugly. This year everything gets benign neglect.

Southern NH here and a little colder than you but not much. I haven't had much luck with overwintering in planters. I have grown Black Cherry in the past and like most floribundas I found it to be not so hardy, so I don't have much hope it in an unsheltered planter.. This is a bit of trouble, but roses growing in planters will lift our pretty easily with the root ball intact. If you have a spot in your yard that will accommodate, you could give it a temporary winter home. Dig a hole and line it with landscaping fabric (to make the spring transplant easier). Mound soil high among the crown of the plant. Pluck it out and put it back in the planter in the spring.

I grow some roses in planters as annuals and this might be something for you to consider. Black Cherry is a really nice rose and it's getting hard to find, so it's worth attempting to overwinter it.

Best of (Irish) luck!

Di