If you are planting erect thorny blackberries, it is more economical to set root cuttings that are about pencil size in diameter and 4-6 inches long. In light sandy soils, plant the cuttings 4-6 inches deep. On heavier clay soils, plant the cuttings 3-4 inches deep. Plants grown from good root cuttings are strong and will come into production as early as one year old sucker plants. If plants are dry upon arrival, soak the roots in water for several hours before planting.
Mixed fertilizers are satisfactory for blackberries.
For best results, apply fertilizer in early spring when growth starts and again in summer just after harvest. For late-ripening thornless blackberries, apply the fertilizer mix no later then July. This is to avoid forcing a late season growth that will be subject to winter injury. For the first year or two, before the root systems of the plants develop fully, spread 3-4 ounces of fertilizer mix in a 12 inch radius around the base of each plant. Mulching reduces the frequency of watering and aids in the control of weeds and grasses that compete for moisture and nutrients.