I think I messed up bad, this was the first year I winterized roses (I
live in
Michigan). I cut them down to about 6 inches from the ground and then
placed
old plastic pots on top of them. I then cut slits in the top and filled
them
with black pine mulch. When I removed the pots yesterday I found the
roses in
terrible shape, the stems seem to all have rotted. I think I really
screwed up

This does not sound like something one just makes up on the fly so I have to
ask -- who/what told you to do this?

To properly winterize your roses (assuming you really need do anything)
simply covering the bulbous part of the stem (the bud union) with mulch will
generally suffice. In more severe climates, you may need to use a rose
collar and/or protect the canes however even these solutions do not
completely cover the entire plant with mulch. Additionally, timing on this
is important as well.

My roses have already begun to leaf out and grow stems (haven't seen any
buds yet) and I'm down in zone 6a. If you haven't seen any growth by the
end of the month, then I'd say it's time to dig them out and buy
replacements.

James