To maximize yields, raspberries must be properly pruned in spring and summer. The pruning procedures for red, black, and purple raspberries are based on the fruiting characteristics of the plants.
Summer pruning of raspberries, though overlooked by many gardeners, is vital. After the last summer harvest, promptly remove the old fruiting canes of all raspberries at the soil surface and destroy them. Removal of the old fruiting canes helps control diseases. Their removal also permits more light to reach the new shoots, resulting in higher yields.
Pinch out or cut off the shoot tips of black and purple raspberries when the new shoots reach a height of 36 to 48 inches. Remove about 3 to 4 inches of the shoot tips. This pinching encourages lateral shoot development and increases the fruiting surface area. Since all new shoots will not reach the desired height at the same time, it will be necessary to go over the planting about once per week from late May to late July. Shoot tip removal can be discontinued at the end of July. Those canes which develop after July will be small, weak, and unproductive and should be pruned out the following spring. (The new shoots of red raspberries should not be pruned in this manner.)
This article originally appeared in the June 16, 1995 issue, p. 87.