In terms of the modern blackberries that fruit on primocanes, you could do it either way. 😄 The floricane crop will be harvested in late spring/early summer, whereas the primocane crop is harvested in late summer/early autumn. Double cropping does not reduce the yield of primocanes, and if you cut down the canes after the primocane crop, the next year you’ll get a bigger primocane crop. So, for those primocane fruiting varieties, you could grow them either way and still have berries.
In terms of the modern blackberries that fruit on primocanes, you could do it either way. 😄 The floricane crop will be harvested in late spring/early summer, whereas the primocane crop is harvested in late summer/early autumn. Double cropping does not reduce the yield of primocanes, and if you cut down the canes after the primocane crop, the next year you’ll get a bigger primocane crop. So, for those primocane fruiting varieties, you could grow them either way and still have berries.