Question
I live in Minnesota (Zone 4)
About 5 years ago I planted a couple of shrub roses. I believe they're called "Knockout"
They seemed to flourish with minimal winter protection.  Until this year.
This spring I trimmed back all the old stems to about 8-to-10 inches high.
Some of the stems are green a few inches above ground but no new leaf growth is coming.
Sould I give up on them?

Answer
Knockout is rated very highly and is hardy past your zone so it should come back for you.
If a rose doesn't go into the winter hardened off then it will be half dead in the spring. Using fertilizer after the end of June in your area keeps the canes from hardening off enough to get through the winter. Also somtimes the fall weather freezes and warms up and that also causes problems. However roses can come back from one inch of cane. All this does is delay the normal time of blooming. I would fertilize them now but pull back by the end of June then don't cover or winterize them until you get a hard frost. The definition of a hard frost is when both the soil is below freezing as well as the air. Covering them sooner tends to make a greenhouse effect on the plant.
Hope this helps. Lynnette