Blackberries are a welcome treat on a hot summer day. But left untended, blackberry patches can become a riot of brambles with little fruit. A well-tended blackberry patch is easy to harvest, the canes are healthy and productive and you will get bigger and juicier berries than from an untended patch. Thornless and regular (brambles with thorns) blackberries are pruned in the same way. The first-year vegetative brambles, called primocanes, are tipped or pruned back to produce sturdier canes with lots of lateral branches. The canes that produce fruit, 2-year-old floricanes, are pruned to the ground after harvest. Blackberries are biennial plants; this means they produce fruit on 2-year-old canes. You must have both 1- and 2-year-old canes growing together to harvest fruit yearly.
Prune thornless blackberries for the first time after planting. Remove dead or broken canes cutting them off at the ground. If your blackberry plant has more than eight canes after removing the dead and broken canes, select the strongest four canes to keep and prune the rest back to the ground. Prune the remaining four canes back to 6 inches.
Cut primocanes (first year vegetative canes) back to 48 inches in June or July. If you are growing erect (non-trellised) thornless blackberries, cut primocanes back to 30 inches.
Remove floricanes (canes that have borne fruit) after harvesting all the fruit. Use loppers or a pruning saw to remove canes at the ground.
Remove excess primocanes when you remove floricanes. Select the strongest 4 to 8 canes to bear fruit the next year and cut the rest back to the ground.
Cut back lateral or side shoots to 12 inches in early spring before the thornless blackberry starts to leaf out.