In the Garden:
Southern California Coastal & Inland Valleys
Pruning and trellising your boysenberry canes in winter will encourage a bumper crop.
Pruning Fruit Trees and Vines
January is the time for pruning deciduous fruit trees and cane berries. The basic guidelines for pruning trees during their winter dormancy are to remove crowded or crossed branches; to open the center for good light exposure and airflow; to repair structural weakness; and to remove vigorous, vertical-growing branches (watersprouts). The height or width of the tree can also be reduced. Take care not to leave stubs or overprune in any single year, as this encourages excessive new foliage and less fruit.
Pruning cuts that are under 1-1/2 inches across don't need protective covering. Just be sure to prune on a day that's dry and sunny so the natural callousing of the tree can properly seal the wound. Paint wider cuts with an off-white or sand-colored interior latex paint that has a matte finish, not a glossy one. Avoid black asphalt substances or dark-colored paint, especially on south-facing surfaces, because they will concentrate the sun's heat and kill the tissue that the tree is trying to heal.
Pruning citrus trees requires a different approach. They only need minor pruning of dead or crossing branches. Heading back branches -- cutting off only portions -- will stimulate more bushy growth and remove wood that would have blossomed and set fruit this coming season.
Cane berries are most easily pruned when all their leaves have fallen off and the buds have just begun to fill out. The dead canes and the plant structure are obvious, and the thorns are more easily avoided. When clipping away all the dead growth at the bases of the plants, be careful not to injure the new pink shoots. After anchoring the top of the branch at the top horizontal trellis, prune each strong cane about 6 inches above.
Spread and re-anchor the upright canes evenly along the trellis in order to keep the area open for good ventilation and promote the even spread of developing foliage. I use my Mom's old spring clothespins, which are easily readjusted to pull the cane taught without the hassle of untying and retying string or retwisting wire.
This pruning and trellising procedure will encourage strong growth of fruiting vines but not of unnecessary foliage. Although cutting down all dead and growing vines at the soil level in a clean sweep is an easy approach, it encourages weak bushy growth with only a few berries setting very low on the plant.
An acceptable variation of this easier approach would be to clean-cut half of the berry vines every two years. Then, you'll always have a year-old patch to bear fruit the following summer, and can clear the other patch by clean-cutting.
I've avoided the whole thorny issue by replacing my folks' original plants with thornless varieties of boysenberries. Any time one reverts to thorniness, I gleefully rip it out.
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