Highbush Blueberries

General Information

There are two types of blueberries grown in New England. Highbush blueberry (Vaccinium corymbosum) is discussed here. For information on lowbush blueberry (V. angustifolium, V. myrtilloides), contact Lily Calderwood at the University of Maine Cooperative Extension in Orono, Maine.

New England is considered the northern edge of the climatic zone in which highbush blueberries can be grown. As a result, a number of disease problems associated with cold stress, particularly canker diseases, are more common here than in other blueberry growing areas. High soil acidity (low pH) and relatively high organic matter are essential for optimum production.

Blueberry has very specific soil requirements, dictated by its unique root structure. The blueberry root system is composed primarily of fine, fibrous roots near the soil surface. These fibrous roots lack root hairs, so the root system has a relatively low absorptive capacity. Blueberry roots are unable to penetrate compacted soils and have limited tolerance to excessively wet or dry soils. The shallow root system is sensitive to both high and low temperature extremes.

Ideal blueberry soil is a well-drained, yet moist sandy loam soil with a pH of 4.5 to 5.2. If pH reduction is necessary, elemental sulfur can be broadcast and incorporated in advance of planting. Soil organic matter levels should be augmented through the use of pre-plant green manure cover crops and the addition of peat moss at planting. In addition, a layer of organic mulch (wood chips, bark, sawdust, pine needles) 3 to 4 inches thick helps to protect roots from high temperature injury in summer and cold temperature injury in winter as well as reduce moisture stress and suppress weeds.

Fertilizer is generally applied in a split application, reducing the risk of root burn and pollution runoff that can accompany a single large application. Half of the total fertilizer needed is applied at bloom and the other half is applied one month later. Late applications of nitrogen fertilizers (after July 1) should be avoided, because they can promote fall growth, delay hardening, and increase chances of winter injury. Since nitrogen is generally the only nutrient needed, ammonium sulfate (21% N) or urea (45% N) are used as the principal fertilizers.

Proper pruning maintains the productivity of highbush blueberry plantings. Young bushes do not need pruning during the first 2-3 years, but after that, bushes should be pruned annually when dormant, prior to budbreak in the spring. Damaged or old canes that are no longer producing strong new wood should be removed at ground level. The goals of pruning are to establish a balance of canes (or main stems) of different ages, to remove non-productive wood, and to allow good airflow to minimize pest and disease problems. Check with your Cooperative Extension office for details of proper varieties and cultural techniques for highbush blueberry.