Jan Maas: Growing blueberries in Northern Minnesota
Blueberries are becoming an increasingly popular fruit to grow in our Northern Minnesota region. Their health benefits are well known, being rich in antioxidants as well as providing 300 percent of the recommended amount of vitamin C in each one cup serving. Blueberry bushes are also attractive in the landscape with glossy green leaves in summer that turn a rich red in the fall.
Blueberries do require special growing conditions. They need a well-drained, loose, highly organic, acidic soil with a pH between 4.0 and 5.0. To check the pH of your soil, do a soil sample and send it to the University of Minnesota soil testing facility or you can purchase a pH meter and do the test yourself. If your soil has a pH of less than 7.0, it can be amended to bring it down to the necessary number. A pH greater than 7.0 would be too difficult to amend, but a raised bed filled with acidic soil would work fine. If the soil pH falls between 5.0 and 7.0, the soil can be amended simply by adding 4 to 6 inches of peat to the top 6 to 8 inches of soil; doing this also adds organic matter. Adding sulfur compounds also will acidify the soil. Remember that all soil amendments need to be done before planting the blueberries. If the soil requirements are not met, the blueberries will grow poorly and leaves turn yellow.
A mostly sunny to full sun site, preferably away from large trees, is required for strong growth. The roots are shallow and an inch of water per week is required to maintain growth. Mulching helps to keep soil moisture from evaporating and soil temperatures cool. Pine needles are a good choice for mulch since they are already slightly acidic, but straw or peat can also be used.
There are a number of blueberry cultivars available. Be careful when you select one and make sure it is hardy in our zone 3 area. There are several that were developed by the University of Minnesota that are suitable. If you purchase your plants locally, the nursery will be able to direct you to proper cultivars. It is helpful to plant two cultivars for cross pollination to increase the size of berry production. Plant the bushes in late April or early May about four feet apart. Put them deep enough into the planting holes so the roots can be covered with three to four inches of soil, water them thoroughly, tamp the soil firmly around the plant, and apply mulch.
Blueberries are long lived plants, lasting 30 to 50 years. During the first two years of growth, help them to get established by removing blossoms thus allowing them to put their energy into root and top growth. The bushes are slow growing and may take 8 to 10 years to reach maturity. They will need fertilizing to maintain plant health. Use an acid producing fertilizer that is suitable for azaleas or rhododendrons. Ammonium sulfate is a good choice, follow manufacturer’s instructions on how much to use. Do not fertilize after the blooming period as this may encourage late growth in the fall that may be susceptible to winter injury. Pruning in early spring will help to keep the bushes shapely and strong. Fruit is produced on one-year-old wood so maintaining four to six healthy main branches is important to continue good fruit production.
Blueberries are fairly insect pest and disease free if kept healthy. However, birds can wipe out a crop if netting isn’t used and rabbits and deer enjoy nibbling on the shoots so appropriate measures are necessary.
Master Gardeners will answer your gardening questions via a voicemail service. Call 444-7916, leaving your phone number, name and the nature of your question. A master gardener will give you a call to speak with you personally. Seek horticultural information on the University of Minnesota Extension www.extension.umn.edu/gardeninfo