Proper pruning of raspberries is essential. Pruning produces higher yields, helps control diseases, and facilitates harvesting and other maintenance chores. Pruning procedures are based on the growth and fruiting characteristics of the plants.
The growth and fruiting characteristics of the raspberry plant are rather unique. The plant's roots and crown are perennial, while the stems or canes are biennial. Each spring, purple, black, and red raspberries produce new canes from buds located at the base of the previous year's growth. Red raspberries also produce new shoots from buds located on their roots. The individual canes live 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. With the exception of fruit color, the growth and fruiting characteristics of yellow raspberries are identical to red raspberries.
All raspberries should be pruned in March or early April. Late winter/early 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. If the canes have suffered little winter dieback, remove the top 1/4 of the canes. Cane-tip removal or "heading-back" prevents the canes from becoming top heavy and bending over under the weight of the crop.
Red raspberries sucker profusely from their roots. To prevent the planting from becoming a wide, unmanageable thicket, red raspberries should be confined to a one- to two-foot-wide hedgerow. Shoots growing beyond the one- to two-foot-wide hedgerow should be destroyed 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 pruning option provides both a summer and fall crop.
Fall-Bearing Red Raspberries (One Crop System)
Prune all canes back to ground level in March or early April. While the plants won't produce a summer crop, the late summer/early fall crop should mature one to two weeks earlier. Also, total crop yield is typically larger utilizing the one-crop system versus the two-crop system. Maintain the plants in a 1- to 2-foot-wide hedgerow.
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 (side) branches to 12 inches in length for black raspberries and 18 inches for purple raspberries.
When pruning is completed, remove the pruned material from the garden area and destroy it. Removal and destruction of the pruned material helps control raspberry diseases, such as anthracnose and spur blight.