II would leave the red raspberries alone. Blackberries' main shoot can be cut off at 3 to 3½ feet high to get more side shoots.

The main reason I ask is to get more and bigger fruit. My blackberries are big but there are not many. My raspberries are small (not tiny) and I get a fair amount. I should have mentioned that in my first post sorry.

One might think that removing old canes that won't produce fruit will increase fruit production, if just because the plant isn't wasting resources on canes that aren't going to do anything. Just FYI, I'm pretty sure that blackberries that don't get much sun will not be productive, fruit-wise. Full sun is important.

Mine probably get 6 hours of sun - maybe a little more.

Do you know if you have biennial vines or a mix? All of your plants may not produce the same way, and may need to be pruned differently. Need to figure out the best way to prune for each type.

Isons Nursery basic info.

I have a mix.