At least half of the nitrogen should be in organic form, which becomes available to the plants over a period of time. One of the best nitrogen sources is ammonium sulfate which helps acidify the soil.
Ammonium sulfate, at the rate of 2 oz should be spread in a circle around each plant about 6 to 8 inches from its base just before the buds begin to swell the second spring. The use of excessive nitrogen should be avoided. Fertilization should be based on results for soil and foliar analysis.
The fertilizer should also contain about 2% magnesium oxide represented by a fourth number, such as 10-10-10-2.
Fertilization of blueberry bushes