Proper pruning of raspberries is essential to obtain top yields. Pruning produces higher yields by increasing berry size. It also helps control diseases. Pruning procedures are based on the growth and fruiting characteristics of the plants.
The growth and fruiting characteristics of raspberries are unique. The plant's roots and crown are perennial, while the stems or canes are biennial. A raspberry plant may grow and produce fruit for many years. However, individual canes live only 2 years and then die.
The shoots of purple, black, and summer-bearing red raspberries are strictly vegetative during their first growing season. The following year, these same canes flower, produce fruit, and then die.
The growth and fruiting characteristics of fall-bearing red raspberries are slightly different. Fall-bearing varieties naturally produce two crops. The first crop is produced in late summer or early fall at the tips of the current season's growth. The following year, a summer crop is produced on the lower portions of these same canes. After the second crop, the canes die.
A number of yellow raspberry varieties are also available. The growth and fruiting characteristics of yellow raspberries are similar to red raspberries. The only difference is fruit color.
All raspberries should be pruned in spring (March to early April). The spring pruning procedures for the different types of raspberries are outlined below.
Summer-Bearing Red Raspberries
Remove all weak, diseased, and damaged canes at ground level. Leave the most vigorous canes, those approximately 1/4 inch in diameter when measured 30 inches from the ground. After thinning, remaining canes should be spaced about 6 inches apart.
Also, prune out the tips of the canes which have died due to winter injury. Cut back to live tissue.
Red raspberries sucker profusely. Plants should be maintained in a 1- to 2-foot-wide hedgerow using a rototiller or spade.
Fall-Bearing Red Raspberries (Two Crop System)
Follow the same pruning procedures as described for the summer-bearing red raspberries. This procedure allows you to obtain both a summer and fall crop.
Fall-Bearing Red Raspberries (One Crop System)
Prune all canes back to ground level in early spring. While the summer crop is lost, the fall crop should mature one to two weeks earlier.
Maintain the plants in a 1- to 2-foot-wide hedgerow.
Total crop yield is typically larger utilizing the one-crop system versus the two-crop system.
The pruning of summer-bearing and fall-bearing yellow raspberries is identical to their red raspberry counterparts.
Black and Purple Raspberries
Remove the small, weak canes, leaving only four or five of the largest, most vigorous canes per clump or plant. Cut back the lateral branches to 12 inches in length for black raspberries and 18 inches for purple raspberries.
The pruned material should be removed from the garden area and destroyed.
This article originally appeared in the February 7, 1997 issue, p. 9.