Blackberry pruning immediately after harvest. Click image for larger view. Fertilization is limited to nitrogen. It is best applied in small frequent amounts in a band along the row, beginning at bloom. An initial soil test will indicate some deficiencies as well as pH. If soil pH is over 8.0, blackberries can show iron chlorosis, which is corrected with soil applications of Fe 138 Iron Chelate or foliar iron sprays every three to four weeks.
Irrigation is essential for new plantings and mature bearing plants.
Drip irrigation lines can be buried at planting time, or laid on top of the ground beside the plants and covered with mulch. Begin irrigation in March or April and reduce watering by September in order to slow new growth and allow hardening of the canes. Infrequent winter irrigations may be needed during drought years. Weed control is necessary to maximize yields and minimize harvesting problems. If there are perennial weeds in the planting area, these should be killed before planting.