Do not apply high rates of granular fertilizer after late June or winter injury can be increased. If vigorous nursery matured tissue cultured plants and compost is incorporated, a low rate of nitrogen should be used. When using injected fertilizers in microirrigation systems, use one half the rates suggested. Where rainfall equals or exceeds daily evaporation in August and September, irrigation should end in mid-August. Broadcast 40 to 70 pounds of actual N in the second year and later years based on vigor of the current years' fruiting canes height and diameter.
Red raspberries can be seven feet high for optimal production.
Thornless blackberries may require less fertilizer. Use low rates on vigorous plants growing on silt loam soils with high organic matter. As the drive row distance decreases the amount of linear feet per acre increases. Thus, higher amounts of nitrogen may be required for narrow rows. You may wish to adjust the amount of actual nitrogen by these amounts.