I bought a small mini-rose
at a grocery store, and it dropped all it's leaves. The stem stayed green, so I watered every time I remembered (not terribly often, but enough I guess) and it began sprouting new leaves in spring
. As a really shot-in-the-dark guess, I think it lost the leaves from too little light, because I kept it indoors. It's still growing
slowly (now outside in bright shade), and hasn't bloomed, but it's surviving. Each season, I'll try and find a slightly sunnier spot for it.
Perhaps, if the change in light over the roses
was large, that's why they dropped their leaves?
Anyway, the moral is, if it's green, don't give up!