Highbush blueberries produce as many as 15 pounds of berries yearly when mature, but need special soil conditions in order to thrive. Most soil types including heavy clay can be amended to provide the right level of acidity, high organic matter and good drainage blueberries require. Few pests or diseases affect this American perennial, but yields suffer unless plants receive frequent irrigation and deep mulch.
Test the pH of the soil several months before planting blueberries. County Agricultural Extension Services test soil samples for landowners. Soil type and calcium level affect the amount of sulfur or aluminum sulfate needed to bring the PH between 4.5 to 5.2, the correct acidity for blueberry plants. Ask the extension agent for the recommended treatment levels for growing highbush blueberries on your planting site. Ninety days after application, test the acid level again to be certain the treatment worked.
Mark planting sites in a north to south row, leaving 6 feet between plants. Leave enough space between rows to allow transportation of mulch to the bushes. With a spade or posthole digger dig planting holes 24 inches deep and 18 inches across. Mix one gallon of wet peat with the excavated dirt before proceeding with planting.
Check the highbush blueberry plant for root damage and prune out any injured roots. Make a mound of dirt in the bottom of the planting hole tall enough to support the bush at the same level it was planted in the nursery. Spread the roots of the bush out over the mound. Push the remaining dirt and peat mixture into the hole, pressing firmly over the roots of the bush to eliminate air spaces. Water thoroughly to settle the soil in place.
Mulch the new plant six inches deep with straw, pine needles or hardwood sawdust. Pull the mulch back at least three inches from the stem of the blueberry bush. Highbush blueberry roots very shallowly, with new roots spreading out beneath the mulch at the surface of the ground. Deep mulch protects the bush from heat stress and maintains a constant moisture level. Mulch decays gradually--when the layer drops to three inches in height, add more.
Never place extra fertilizer in the planting hole when planting blueberries. Add phosphorous or potassium only if soil tests show deficiencies in those elements. In late April after planting dress each bush with one ounce of ammonium sulfate. Spread the fertilizer in an area a foot and a half wide around the bush, but not touching the stem. Repeat the application in June and again in July. In following years as the bushes mature, increase the ammonium sulfate amount by 0.1 pounds per year of growth. At maturity the plants receive 0.3 pounds of ammonium sulfate fertilizer twice a year--once during the bloom and again a month and a half later in the season.