The Highbush Blueberry Plant
Highbush blueberries are perennial, long-lived, deciduous, woody shrubs. They belong to the family Ericaceae, which also includes such plants as cranberry, azalea, rhododendron, and heather. Like the other ericaceous plants, blueberries thrive in acid soils and do best in soils with a pH between 4 and 5. Cultivars require from 120 to 160 growing degree days to ripen fruit.
The highbush blueberry is a shallow-rooted plant, characterized by a lack of root hairs. The fine, fibrous roots of the blueberry require an open, porous soil for ease of growth. Blueberry roots are associated with mycorrhizal fungi in the soil. These fungi aid the blueberry plant in nutrient absorption. Many of the soil management practices recommended for blueberries may actually benefit the fungus, not the plant.
Root growth begins in spring when soil temperatures reach about 43 F; often this coincides with bud swell. Root growth continues through late spring, but slows during fruit development and maturation. Most root growth occurs from after harvest through fall, until soil temperatures fall below 43 F. Most blueberry roots are found within the dripline of the bush and in the upper 18 inches of soil.
In general, the climate and soils between the coastal ranges and Cascade Mountains in Washington and Oregon are ideal for blueberries. There are, however, areas where soils are not suitable, such as areas of compact clay soils that allow very poor internal drainage and root penetration. Coarse sandy or gravelly soils present problems because of their poor nutrient and water-holding capacity. There is potential for commercial blueberry production in some regions of Idaho; site selection and cultivar are important.
Cultivated blueberry plants usually require 6 to 8 years to reach full production and are 5 to 10 feet high at maturity. Vegetative growth begins in the spring with bud swell. Shoots grow in flushes, showing rapid growth, then stopping as the apical bud aborts. A bud near the tip of the shoot will continue to grow. Shoots may have from one to several flushes during the season.
In mid-summer, shoot growth slows and several buds along new shoots differentiate into flower buds for next year’s crop. Flower bud formation begins at the shoot tip and continues downward. Flower buds are large and almost spherical, whereas vegetative buds are pointed, small, and scale-like. Each flower bud contains from 5 to 10 potential flowers.
Flower bud formation continues until temperatures become too cool in fall. Both flower and vegetative buds require a period of dormancy, from 850 to 1,000 hours between 32 F and 45 F, before growth begins again the following spring.
New canes develop from the crown (base) of the blueberry plant in early spring. These shoots are extremely vigorous and often are the “renewal” wood for subsequent years’ production.
Blueberry plants flower in spring, with flowers at the tip of canes and the tip of the cluster opening first. If pollination does not occur within 3 days after flower opening, fruit set is not likely to occur. Thus, growers should saturate the planting with bees at bloom time. Although blueberries are self-fertile, cross-pollination increases fruit production for many cultivars, resulting in earlier ripening and larger fruit. With better cross-pollination, more seeds develop, resulting in larger fruit.
Fruit development occurs for about 2 to 3 months after bloom, depending on cultivar, weather, and plant vigor. Sugar content of fruit will increase during maturation to about 15 percent when fruit is ripe. Fruit size continues to increase after fruit turns blue, due mainly to water uptake. Drought conditions during fruit ripening will reduce fruit size and may affect flavor. Irrigation during fruit filling and ripening is thus important.
Ripening is closely related to fruit quality. During ripening, changes in cell walls result in berry softening; this softening improves palatability, but also increases fruit susceptibility to physical damage.
Accumulation of sugars during ripening increases sweetness. Sugar content does not increase after harvest, but acids are broken down during ripening, thus decreasing tartness. Fruit flavor, much of it associated with the skin, increases during ripening, but not after harvest. Postharvest shelf life of blueberry fruit is increased by rapidly cooling fruit after harvest.
Yields can be as high as 20 tons per acre (T/A), although yields of 7 to 8 T/A are typical of mature plantings. Note that yield data in table 3 are from an average of all fields, including immature plantings.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks.