I’m interested in this as well. My blackberries only seem to put up 1 or sometimes 2 new primocanes. I haven’t had much experience with blackberries but over the last few years this has been the case.
Black raspberries sprout new canes usually from the crown, they don’t sucker like other rasps or blackberries. You ought to see a few new canes over the next month or so. I’m seeing new red and yellow rasp and blackberry canes now, but no black rasp canes yet, but it’s still a bit early.
For me, my blackberries send up lots of canes, and to lesser degree red/yellow rasps, and the black rasps the least.
@BG1977 – I have a black raspberry (not sure what variety)… it was supposed to be a fall gold… but obviously not. That is what mine looked like on 4/18. It has several primocanes coming up from the crown… and others here suggested I just wait a month or so and the keepers would be more obvious then, and the ones to prune out too.
Back in March, it had done some tip rooting, and I got some props from that… but when I checked it mid April, there were some root shoots up too. Below is what one of those looked like.
It was close enough to my row to keep… so I will probably keep 3 of the best primocanes from the crown, and possibly this root shoot too.
I am in zone 7a, southern middle TN… and may be a little ahead of you. With more time you may see more primocanes off the crown, and possibly some root shoots too. Good Luck !