I'm afraid I cannot answer your question, but I do have an alternative. Where I live (Azores Islands) we simply put a branch in the ground and about 40 percent of the time new roots will develop. If this is an option, you might try it.

[img]http://home.judson.edu/academic/spinner/rose/light&darkrose.jpg[/img]
Confederate Roses are being cultivated from cuttings of about twelve to fifteen inches taken prior to the first frost cuttings were placed in glass jars till they had enough roots and follage on top. Then potted and planted when fear of frost has past.
I found this on the www...
Toni