To maximize yields, raspberries must be pruned in spring and summer. The pruning procedures for red, black, and purple raspberries are based on the growth and fruiting characteristics of the plants.
Though overlooked by some gardeners, summer pruning of raspberries is extremely important. After the last summer harvest, promptly remove the old fruiting canes at the soil surface. To help reduce disease problems, the pruned material should be removed from the garden and destroyed.
Pinch out or cut off the shoot tips of black and purple raspberries when the new growth reaches a height of 36 to 48 inches. Remove approximately 3 to 4 inches of the shoot tips. Pinching encourages lateral shoot development and increases the fruiting surface area, resulting in higher yields. Since all new shoots will not reach the desired height at the same time, it is necessary to go over the planting approximately once each week between late May and late July. Discontinue shoot tip removal at the end of July. Canes that develop after July are small, weak, and unproductive. These small, weak canes can be pruned out the following spring.
This article originally appeared in the June 16, 2000 issue, p. 71.