Pruning Raspberries in the Fall
Question: Should I cut down my raspberry bush now or wait until next year? C.W.
Answer: Raspberry pruning depends on the type of berries you’re growing.
Ordinary red and yellow raspberries should be pruned twice a year. In fall remove all of the canes that produced fruit this year. Any older canes should be removed too. These canes will not produce fruit again and can be a source of diseases and insects. Pruned canes can be backyard composted, burned, buried or sent to a municipal composting facility. Before the buds swell in spring, but after the worst of winter cold is past, thin out the remaining canes. Remove at the ground level all weak, spindly canes. Keep the largest canes which will bear the most fruit. Fruiting canes should be spaced at six to twelve inch intervals for row grown raspberries. Canes supported on a wire trellis should be pruned to five to six feet tall. Cut unsupported canes back to three to four feet high.
Fall-bearing, also called ever-bearing or primocane-bearing, produce two crops of berries per cane. New shoots bear fruit in fall at the tip of the cane, and again the following spring lower on the cane. For this type of raspberry, leave the canes uncut in fall. In early spring before growth begins thin out the weak canes. Cut other canes back by about a quarter of their height. Using this alternative, you will get a small crop of raspberries in the early summer on the old canes and a bigger crop of fall berries on the new ones.
Another option for ever-bearing raspberries is cut all the canes back to the ground after fall harvest. New canes will sprout the following spring and bear in fall. The large fall harvest more than compensates for the lack of fruit in early summer.
Black and purple raspberries are pruned in fall after harvest is completed. Remove all canes that bore fruit this and past years by cutting off at the ground line. After pruning, only new canes, which have not produced fruit, should remain.
Before growth starts in spring, choose four or five large healthy canes on each plant to be fruit producers. Completely remove all other canes. On the remaining canes prune the side branches back to 12 inches long on black raspberries or 18 inches long on purple raspberries.
When the canes on your purple raspberry reach 30 inches tall (24 inches for black), pinch/prune 2 to 3 inches off the top growing tip of each cane. Pinching forces growth of side branches for more fruit production and easier picking.
Check out the publication: Growing Raspberries http://hort.uwex.edu/articles/growing-raspberries-wisconsin