Both the harshness of Minnesota's winters and the composition of the state's soil make growing blueberries a challenge for Minnesota gardeners. Choosing the right plants and getting creative with soil preparation, however, can bring a bountiful blueberry harvest to the north country.
Blueberries need acidic soil with a pH level between 4 and 5. Acidic soil is rare in Minnesota, but amendments can bring soils with native pH levels between 5.5 and 7 to a level of acidity that will work for blueberries; add 4 to 6 inches of acid peat to the top 6 to 8 inches of sandy soil to increase its acidity. Adding 1 or 2 pounds of sulfur to 100 square feet of soil will lower its pH by one point, as well.
Soils with pH levels above 7 are common in western Minnesota, and those soils probably cannot be made acidic enough for blueberries. Instead, plant blueberries in raised beds filled with a mixture of 2 parts acidic compost and 1 part loamy soil.
Site Conditions and Planting
In late April or early May, plant blueberries in a location with well-drained soil and that gets sunlight for at least three quarters of the day. Space plants 3 to 4 feet apart, and cover the top of the roots with 3 to 4 inches of firmly packed soil. Cover the base of the plant with 2 to 4 inches of mulch, and maintain the mulch through the growing season.
The University of Minnesota has developed seven blueberry cultivars that are suitable for growing in Minnesota. They are "Northblue," "Northcountry," "Northsky," "St. Cloud," "Polaris," "Superior" and "Chippewa." Another cultivar that can withstand Minnesota winters is the University of Michigan's "Northland."
These varieties are half-high bushes, which are crosses between northern highbush blueberries (Vaccinium corymbosum) and lowbush blueberries (Vaccinium angustifolium), and they're hardy in U.S. Department of Agriculture hardiness zones 3 to 7. Southern Minnesota falls into USDA zone 5, and the northern part of the state is classified as USDA zone 3, so they should survive in all parts of the state.
Fertilization and Watering Needs
Water frequently to keep the soil around the plant moist, but avoid overwatering so that the soil does not become saturated. In typical conditions, plants will need about 2 inches of water a week.
A single application of fertilizer early in the season will encourage plant growth and fruit production. Don't fertilize after the plant has finished blooming and setting fruit, as late fertilization encourages late-season growth, which can leave the plant vulnerable do cold damage during the winter.
Blueberries prefer acid fertilizers, such as those intended for azaleas and rhododendrons, and you should choose a fertilizer that has ammonium sulfate as its source of nitrogen rather than ammonium nitrate.
A month after planting, use 1/10 pound of a 12-12-12 dry fertilizer per plant, and then use 2/10 pound at the beginning of the bloom period in the second year. In the third and subsequent years, use 3/10 pound at the beginning of bloom, and then follow up with two applications of 2/10 pound spaced six weeks apart.
Pests and Diseases
Blueberries are not especially vulnerable to insects or diseases, but planting them where there's good air circulation around their leaves will help to reduce the chance of infections. Animals are a bigger problem, however; birds will eat the berries, and rabbits may eat new growth during the winter. Lightweight netting over the plants can help to keep the birds away, and wire cages around the bushes will fend off rabbits.