It doesn't matter much. Leaving the ground exposed allows the soil to heat up on warm sunny days--or chill down during a cold spell.

I leave the old mulch and let it rot into the soil. Most people do. Applying a layer of new mulch helps suppress fungi.

You should put your state and climate zone into your signature. We can help more if we know whether it is cold enough to warrant the collars, and whether you are in a blackspot area or a rust/mildew area.

OK, I see on another thread you are in Wisconsin. A couple of HT-like roses that are hardier and more blackspot-resistant than most HTs are 'Earth Song' and 'Mother of Pearl.'

Thanks so much! Will be looking these two HTs up. I just did. Love, love, love the look of the Mother of Pearl. Not so crazy about the antique type roses which the Earth Song is. My favorite are what look like the long stem roses people get from a florist. Most of my HTs look like those. My favorite were the purple ones (can't think of the name off-hand), but two bushes did beautiful for about 4 years each, then died.

Michael, I think my zone is 5, although in Milwaukee, Wisconsin--it was a lot colder this past winter than a zone 5. So should I keep it a zone 5? Thanks!

I never dispose of our old mulch but let it rot into the ground. I just keep putting down new mulch over top of it when needed...

I used to just keep putting down new mulch over the old--but after years it wasn't completely rotting into the ground & it was nasty, so I raked it all off & started anew. Now, like I said, I use the mulch in the rose collars when I winterize.

You don't need to change your zone because of an atypical winter.

Another rose you might look at is 'Les Sjulin'. It is definitely high centered, but doesn't hold form as long as most HTs.