The shoot tips of purple and black raspberries should be pinched or cut off when the new growth reaches a height of 36 to 48 inches. Remove the top 3 to 4 inches of the shoots. Pinching encourages lateral shoot development and increases the fruiting surface area, resulting in higher yields. Since all the new canes will not reach the desired height at the same time, it will be necessary to go over the planting about once a 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.