If you are thinking about planting blueberries next spring, now is the time to begin preparing your planting beds. Blueberries need acidic soil with a pH of about 4.5 to 5.5. Our Inland Northwest soils tend to be in the 6 to 7 pH range. Soil pH affects nutrients available for plant growth, especially iron. Plants that are grown in pH 7 soils or higher will turn yellow and become stunted. Changing soil pH to meet the blueberry’s needs is a slow process that can take three to 12 months to complete depending on soil temperature and moisture.
The first step in preparing the soil is to get a soil test to determine the existing soil pH. This can be done using either a soil test kit bought at the garden center or by sending soil samples to a lab. The simple home kits aren’t as accurate as tests done in a lab. Basic lab tests can run from a few dollars to as much as $50. It’s best to use labs based in the Western U.S. because of the types of tests they run. If the pH comes back in the 6.5 to 7 range, then it’s better to grow the blueberries in raised garden beds or large pots where you can engineer the soil mix.
The best soil mix for a blueberry bed is a blend of equal parts of commercial garden soil, compost and either peat moss or fine conifer bark. The peat moss and conifer bark tend to be acidic and will be a good starting point for getting the pH to the right level. Because blueberry roots are very fine, the compost helps hold water.
Mix in 3 to 4 pounds of elemental sulfur granules per 100 square feet of bed to further lower the pH. Over the winter, soil bacteria will break down the sulfur into a form that can be drawn up by the plants. Granular elemental sulfur is available at local independent garden centers. In the spring before you plant, check the pH again and add more sulfur if needed. Reapply granular sulfur every two years.
Blueberries need a sunny spot that gets some late afternoon shade. Stay away from south-facing walls as they can get too hot. Don’t plant them next to concrete foundations or walls as the lime from the concrete can leach out and adversely affect the pH.
Blueberries need regular watering applied by a drip system set on an electronic timer. Mulching the bed with conifer wood chips will help retain moisture, prevent weed growth and help with pH levels. Once established, fertilize the plants regularly with rhododendron food.
For the best production, blueberries need two different varieties of early, mid- or late-season plants for proper pollination. Early season plants start producing in July while late season plants will start in early September. Be sure to choose plants that are hardy to USDA Zone 5 or lower. Once planted, the bushes will take about three years to begin producing.