Blueberries require a very acidic soil, so before considering how to fertilize the bushes, you need to answer some important questions. A soil test should be done to find out its pH. The Ph level is the most important factor for the success of growing blueberries. It should fall between 4.5 and 5.1; if tt is too high or too low, corrective measures need to be taken, preferably before bushes are planted. Other considerations affecting fertilizer are soil heaviness and level of the water table.
Test the soil with a test kit or take a sample to a county extension center for testing. Provide samples of soil from at least 12 inches below ground as blueberry roots will grow 12 to 16 inches.
Add elemental sulfur to the soil if the results show the pH is too high. If your soil is sandy, you will need 3/4 lb. for each pH point over 4.5 per 100 square feet. You will need 1-1/2 to 2 lbs. in loamy soil, and 3 or more lbs. in clay soil. This should be done at least six months before planting. Retest the soil right before planting. If sulfur is added at planting, carefully work it into the soil around the bushes at least 10 away from the trunk.
Use 1 oz. of 10-10-10 fertilizer one month after planting. Place it in a ring around the base of the plant but not touching the trunk. Water in well. Increase to 2 oz. the following year and through year four, and then increase to 1/2 lb. per year. Apply the fertilizer in April each year.
Apply 1 or 2 oz. of ammonium sulfate each spring before the growing season begins. This will help keep the pH down and supply the bush with nitrogen.
Mulch with clean straw or wood chips around the plants but not touching the trunk. This will help keep weeds down, retain moisture and add nutrition to the soil as it decomposes.