How to Trim Raspberry Plants

Prune summer bearing raspberries immediately after the crop has been harvested. Cut the fruit-bearing canes to ground level. The Washington State University Extension recommends thinning the new canes, or primocanes, to 10 to 12. Once pruned, tie the new canes to a trellis in preparation for next year's harvest.

Prune fall-bearing raspberries by cutting all canes back to ground level in the fall once the plant has gone dormant. According to Washington State University, this prevents winter damage to canes and reduces the risk of insects and disease. The University of Illinois suggests waiting until March or April before cutting canes back to the ground and notes that this delays fall fruiting, but increases yield.

Prune black and purple raspberries in the summer by cutting back the top 3 to 4 inches of each cane once they have reached a height of 2½ to 3 feet. This encourages side shoots that also produce fruit. Once canes have produced fruit and harvesting is complete, cut old canes back to ground level. Thin the remaining canes by removing any that are less one-half-inch in diameter.