Blackberry cuttings sprouted but not rooted
I cut some green blackberry cuttings and put them in rooting hormone, then Miracle-Gro potting soil, and kept them moist. This was in January. The cuttings all sprouted leaves early on, but they never opened (just have sprouted leaf buds all along the stems now) because at one point I let them go dry. After that I kept them moist, though. They are now brown on the outside instead of green.
When I checked today (these are for a trade), not a single one has roots. Some do have teeny fuzzy "hairs" (they stick straight out about 1/16 of an inch, which is the only way I could see them) growing around the part that's been in soil. None have even callused, like my woody Rose of Sharon cuttings did (and which do have roots now).
Any advice? Should I give up?