Properly Pruning Raspberries & Blackberries
According the University of Maine Extension web site, "Pruning is a vital part of maintaining a healthy raspberry planting. This practice greatly inhibits the spread of raspberry diseases and improves fruit quality and yield. During the summer months, regularly remove al
l new canes that emerge outside the desired plant row width of 12 to 18 inches. This improves light penetration and air circulation for the canes in the middle row that will fruit next year. Also remove any canes that show obvious signs of insect or disease injury. In the late winter or early spring, before the buds break, remove all of the old canes that fruited the previous year. These have gray, peeling bark and branches (they are dead and won’t fruit again). Again, remove canes that have emerged outside of the desired 12- to 18-inch row width. Maintaining this narrow row width will assure adequate light penetration and air circulation to promote healthy cane growth and reduce disease problems. Only the most vigorous canes, those with the greatest height and basal diameter, should be left in the row. Continue thinning until only four to five canes per foot of row length remain. These remaining canes should be attached to the trellis wires with twine. Finally, remove all of the plant waste from the field. Plant waste can harbor diseases and insects that may attack the healthy canes.
Everbearing or fall-bearing red raspberries bear a late-season crop on first-year canes. If they are pruned in the same manner as the summer-bearing types, they will bear two crops per season; one in the summer on the second-year canes, and one in the fall on the first-year canes.
Everbearing raspberries can also be managed to produce only the fall crop. Simply mow all the canes down early each spring. During the summer, cut down any new canes that develop outside the 12- to 18-inch row width and thin the remaining canes to about six inches apart, leaving the sturdiest. This technique greatly reduces pruning labor, but also eliminates the summer crop. Unfortunately, most everbearing cultivars, such as Heritage, produce the fall crop too late in the season to escape damage from frost in most of northern New England.
Blackberries should have the growing tips of the new canes pinched off when they reach four feet. This encourages the canes to form side branches, or laterals, which will bear the fruit in the following year. Remove all canes that fruited following harvest. In the early spring, thin the remaining canes, leaving only five to seven of the sturdiest per hill. Cut the side branches back to 12 buds (usually about 12 inches in length) and tie the canes to the wire or post for support.
Remove all plant waste from the field after pruning and destroy it, preferably by burning. Leaving dead canes in the planting will encourage the spread of diseases."
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