Q: When is the best time to prune my blackberry bushes? Our winters here in zone 5 are often harsh. — James M. Milliken, St. Frances, KS
A: Some blackberry varieties, such as ‘Brazos’ from Texas and ‘Marion’ and ‘Boysen’ from the West Coast, are not reliably winter-hardy in your area. If your berry plants suffer heavy winter damage, pruning isn’t the remedy. Replace them with varieties that are hardy in zone 5 and have an erect growth habit. I recommend ‘Navajo’ because it’s thornless; ‘Cherokee’ is dependable, too, though prickly. If you haven’t yet pruned your blackberry row this season, get to work before the plants emerge from dormancy. First, remove any canes (stalks) that fruited last year by cutting them off at ground level; brittle, dead-looking canes won’t leaf out again. Next, remove the spindliest of the greenish new canes, leaving the thickest about 6 inches apart in the row. Also clear away canes that have sprouted outside the row, which should be no wider than 18 inches at its base. Finally, shorten the remaining canes to 4 or 5 feet, and trim side branches to 18 inches. Pruned this way, erect varieties won’t require the support of a trellis.
Blackberries have perennial roots, but their canes live for only two seasons — sprouting in spring, attaining full height the first season, then blossoming and fruiting the second season. Once fruiting is over, in the summer, you can cut the spent second-year canes to insure that they won’t snatch sunlight and water from the new canes you want to encourage. Then, shorten the new canes to 4 or 5 feet to foster emerging side shoots. Raspberries, both red and black, require the same basic pruning, with a few differences. Raspberries are smaller plants, so keep each row only 12 inches wide at the base, and tie the canes (less rigid than blackberries’) to a horizontal wire stretched 4 to 5 feet off the ground. Prune the tips of the canes 3 to 6 inches above the wire.