Blackberries and raspberries require about 1.25 pounds of ammonium sulfate per year, per plant or 0.25 pound of actual nitrogen per year, per plant. Apply fertilizer just prior to an irrigation by banding the fertilizer out 12 inches from the plant. Apply all the fertilizer in the winter or in smaller increments during the growing season, with one application in spring, two applications in midsummer and one more in fall.
In some climate zones, potassium and phosphorous may be limited and may need to be added to the soil. Soils will need to be tested.
Fertilizing tips
If you use manure, compost, or another source of organic fertilizer, apply it in the late fall or early winter.
Inorganic fertilizers out of a bag should be spread over the surface of the soil in the row in early spring just when growth is starting. If plants lack vigor, apply additional fertilizer at bloom.
