Dormant bramble care
Fertilizing and pruning brambles needs to take place before plants leaf out, which means if you haven't yet done so, now is the time. There are three production "systems" for brambles. One for red and yellow raspberries, one for black raspberries and erect blackberries, another for semi erect blackberries.
Red and yellow raspberries- prune twice per year. In early spring, before buds begin to swell, thin all weak canes so that 6-8 strong canes remain per square foot. Cut the remaining canes back to 5-6' if providing support, 3-4' without support. Second pruning is done after harvest. Remove all fruited canes.
There is a system that's been developed for fall bearing red raspberries (Heritage and Caroline type) only. It's very simple and easy. Simply mow off all the canes at ground level each spring, before bud swell. This eliminates much hand labor and eliminates the need of a trellis. However, only one crop (late summer) will be harvested.
Black raspberries and erect blackberries- Prune several times per year. In early spring, prior to bud growth, thin so that there remain 4-6 canes per hill or canes are spaced 8" apart in a hedgerow. Remove old-fruited canes and weak canes. Tip lateral branches of black raspberries back to 8-12", and purple raspberries and erect blackberries back to 12-18". (Lateral branches are where fruit will be produced)
During summer, pinch back tips after they have reached desired height, about 3' tall. If trellised, they can grow somewhat taller. This step is essential as all fruit is produced on lateral growth. Tipping back will encourage lateral growth. As canes grow, continue to tip back.
Semi erect (thornless) blackberries are pruned twice. In early spring, select the best 6-8 canes and prune out weaker ones. Remove any winter killed canes and any lateral branches up to two feet from the soil line. Cut back remaining laterals to 12-18" in length. If the cane is too long, cut back to give room to other canes. Second pruning can be done after harvest when you remove canes that have fruited. Because thornless blackberries are not as winter hardy as thorny blackberries, later pruning is recommended. As new canes develop during the summer, tie them to a trellis support system, as cane growth can reach 12-15 feet in length.
A new type of blackberry has been developed. There are three varieties: Prime Jim, Prime Jan and Prime Ark. These berries can be managed similar to the Heritage type red raspberries. Simply mow them off each spring, before bud break, and they will produce a "late summer" crop. This minimizes the amount of pruning required.
Fertilizing of brambles can occur now. The rule of thumb is to apply 2# of a 12-12-12 or similar fertilizer per 100 feet of row. For non suckering brambles (those that grow from a single hill) apply ½ cup per plant.