Cass writes:

I think I pulled the collar off all at once. That removed the first
increment of mulch. Then I just hosed it off a little every few days. I
always kill any shoots under the mulch if I even think about touching
them, so I use the hose. Took about a week. Good luck with your late
BR's.

Okay, I'll try it. I've got plenty of cardboard at work that should do the job
well. The last bare roots arrived in June when we were having daily rain
storms. They washed off the mulch for me until I got tired of putting it back
on. I did loose two of those roses, not to lack of moisture, they drowned.
Their pots didn't drain properly and by the time I caught it, they were already
too far gone. But I didn't feel too bad, 17 of 19 survived.