A reader asked me why his blackberries didn’t fruit this year. Since blackberries are less cold hardy than raspberries, the flowers might have frozen with a late cold spell. Or, bees may not have been available to pollinate the flowers. On the other hand, ill-timed pruning could be the culprit.
Blackberries grow best in full sun and well-drained soil, high in organic matter with a pH of 6.0 to 6.5 where they are protected from strong hot or cold winds. Hot summer winds can dry out the fruit. Cold winter winds cause winter injury, such as cane breakage or drying out the base of the plant. Blackberries should not be planted in an area where you have grown potatoes, tomatoes, peppers, eggplant, other caneberries or strawberries in the past three years because of the potential for disease.
Blackberries are classified as erect or trailing, based on the way they grow. Although erect blackberries are somewhat self-supporting, both types benefit from trellising. Knowing a plant’s growth habit helps you prune for maximum fruiting.
Blackberry roots live for many years. The canes, on the other hand, grow one year (primocanes) and produce fruit the second year (floricanes). Floricanes die after fruiting and should be removed after harvest. Primocanes need to be thinned for the next year. During summer, when an erect type is 3 feet tall, remove the top 1 to 2 inches of the primocanes. This encourages branching for increased fruiting the following year. Don’t top trailing types. Also, shorten the side branches of erect varieties, but not of trailing ones.
After harvest, remove the fruiting canes of both types. In late winter, when plants are dormant, thin the erect-type primocanes to three or four of the strongest-looking canes per plant. Prune lateral branches on these canes to 12 to 18 inches long.
For trailing types, cut out the floricanes after harvest and thin primocanes to eight shoots per crown. In late fall, after laying trailing canes on the ground, mulch over them to protect them from the cold. Mulch the crowns of both types to protect them from winter drying.
Whenever pruning, remove dead or weak wood at the same time. Seal all cuts with white glue (cheap school glue works well) to prevent cane borers from getting in the stem and killing the plant.
The next free Grow Your Own class at Cooperative Extension is October 3, 6 to 8 p.m., on “Hillbilly Gardening – Gardening Creatively and Frugally” at 2621 Northgate #12. Call 887-2252 to reserve your spot, or email email@example.com.