Theo Asir wrote:

No rose that I know can tolerate a Zone 1
unprotected. The rose w/ the greatest cold
tolerance is the species rose Rosa Acicularis
which grows at the poles and
even it is Zone 2 rated.

Also the Rugosa roses
are known to tolerate -35F tempretures without
protection.

Yes, Rugosas do well here, often unprotected, and we have a thriving
population of "wild" roses--not sure exactly what they are, but they're
everywhere.

Thirdly keeping roses dormant inside heated/unheated
garages or basements is a common problem.
It is not a function of how long you kept it in frost,
as it is the garage tempreture. You indicated in another
post that you garage gets up to 50F. This is way
too warm for a dormant rose. the tempreture needs to be
@ about 25-30F to keep the rose dormant.

Thanks, I wasn't sure if they could stay under freezing like that and
survive.

If you can turn down the heat to the garage
get one of those cushioned play mats from toys'r us
and place the roses one that. This will ensure the
pots don't freeze from contact w/ the ground.

What a great idea! I wonder if that blue insulation foam would work as
well. The hard part about the garage is that the furnace is there and
even when the space heater part is off, it can be pretty warm just from
the furnace. Maybe I'll try building an insulated rose box in the
coldest corner of the garage this fall--try to protect from both extremes.

Alternately you could withhold water and keep
the soil just moist. This too helps keep a rose
in dormancy. DO NOT let it go dry.

Would you suggest covering it with something nonpermeable like a plastic
bag (assuming I could get it around the thorns without poking it full of
holes!). Or would this encourage mildew or parasites too much?

Thank you for such helpful answers and suggestions! My grandfather was
an expert rose man, and I'm sad that I've come to roses too late for him
to have helped me out.
Kim