By Maureen Matt, Butte County Master Gardener, April 24, 2015
Blueberry varieties are often self-pollinating, but fruit set will increase and berries will be larger if two varieties are planted together, so bees can travel and cross-pollinate.
Like azaleas, blueberries belong to the family Ericaceae, and prefer acid soils with a pH of 4.5 to 5.5. Soil sulfur can be worked into the soil six to twelve months before planting, and side-dressed as needed in subsequent years. Peat moss too can be used to adjust acid levels. Soil testing kits are available at local nurseries and, used yearly, can spot when soil corrections are needed.
Most blueberries are deciduous shrubs that grow 4 to 6 ft. tall. Plants can be spaced 3 ft. apart for an informal hedge, or 4-5 ft. apart for individual shrubs. Place year-old blueberry plants in a sunny location. Two plants per person is advised, and some for the birds, unless you net your bushes. Because their shallow roots are 3-4 ft. wide, the soil should be dug this wide and at least 1-2 ft. deep. Amended soil in raised beds also works well.
Lightly roughen up the outside surface of a root-bound plant. Set the soil line of the trunk slightly above soil level to prevent settling. Cover soil with 4-6 inches of mulch to conserve moisture, prevent weeds, and add organic matter. Bark mulch (not cedar), pine needles, acid compost, and sawdust all work well.
Blueberries' shallow, fibrous roots need adequate drainage. Irrigate with soaker hoses, mini-sprinklers, or drip lines. Water is critical from berry development through harvest, also during bud formation in July and August. The amount of water will depend on soil type, drainage, and weather; too much water can result in root rot. For these reasons, frequent testing of soil moisture is recommended.
Take care to prevent over fertilizing. When needed, usually in early and late spring, gently rake back mulch and spread fertilizer on top of soil. Replace mulch and water well. Use a 10-10-10 mix or something similar containing ammonium sulfate and potassium sulfate, both of which are acid-forming. Sprinkle one and one-half tablespoons within 12-18 inches of each plant four weeks after planting. Double fertilizer amounts yearly up to a maximum of five tablespoons per plant.
Organic fertilizers like blood meal, cottonseed meal, fish meal, and alfalfa meal can be used instead of commercial types at a rate of 1 lb. per plant, beginning at the initial planting.
It takes at least three years for a blueberry plant to become established and healthy. Remove all blossoms in the first few years to prevent small berries and spindly growth. Blueberry plants have a naturally bushy form, but the number of branches should be limited to the age of the plant, up to a maximum of six to eight branches for old bushes. Yearly remove one to two branches so that none are over four to six years old.
Southern highbush varieties include the early-ripening Misty, O'Neal and Jubilee; the early to mid-season Sharpblue; and the midseason varities Southmoon and Sunshine Blue. For more information, see http://ucanr.org/sites/gardenweb/Berries/Blueberries.