I have several blueberry plants that didn’t blossom or fruit. I sprinkled aluminum sulfate and ammonium sulfate on them. Now the leaves are falling off and they seem to be going dead. Did I burn them? Will they come back?
There are two basic types of blueberries – highbush and lowbush. Highbush are the cultivated blueberries that grow best in a line extending from Muskegon to the lower end of the Saginaw Bay. Lowbush are the wild blueberries that grow throughout the state and are about 20 inches tall. Blueberries are considered to be a long-term crop as it takes between 8 and 12 years for them to reach maturity. With proper care, they can live for 20 to 40 years. I wonder how old your plants are and if they have ever produced flowers or fruit? Blueberries have fairly specific soil and climatic requirements for good production. Let’s go through these requirements and see if we can solve the mystery of no flowers and no fruit.
First, blueberries must have acidic soil with a pH below 5.5 and do best in soil with a pH between 4.5 and 5. Your soil should be tested before planting and regularly thereafter. If your soil pH rises above 5.1, add elemental sulfur or aluminum sulfate. Several pounds of sulfur or aluminum sulfate are needed per 1,000 square feet to lower the pH one unit. Ideally, your soil should have good drainage with a water table 14 to 22 inches below the surface. Blueberries need a consistent water source throughout the growing season but don’t like “wet feet.” When choosing plants, it is recommended that you choose a 3- or 4-year-old bare-root or container-grown plant, as younger plants have more difficulty getting established enough to maintain their winter viability and will take longer to bear fruit. Young plants are also fertilized differently than the older plants. Again, a soil test is preferable but in the absence of a soil test, these are the recommendations:
- Planting year – 2 to 4 weeks after planting, sprinkle 1 ounce of 20-0-10-5 (NPK magnesium) within 10 to 12 inches of the plant.
- Years 2-3 – Spread 2 ounces of 20-0-10-5 in a 2-foot diameter around the plant.
- Years 4-5 – Spread 3 ounces of 20-0-10-5 in a 3-foot diameter around the plant.
- Years 6-7 – Spread 4 ounces of 20-0-10-5 in a 4-foot diameter around the plant.
- Years 8-9 – Spread 5 ounces of 20-0-10-5 in a 4-foot diameter around the plant.
- 10th year to mature bush – Spread 3 ounces of 20-0-10-5 in a 4-foot diameter around the plant.
On an established planting, apply the fertilizer around the drip line of the plant. On sandy sites, you may want to use two applications of fertilizer: half before bud break and half at petal fall. This will help reduce leaching. If 20-0-10-5 fertilizer is not available, use urea or ammonium sulfate.
Blueberries are self-fruitful and will set fruit without cross-pollination but they do require “busy bees” for pollination and fruit set. Native bees will do the trick in the backyard garden. Regular pruning is necessary for a high yield production. The most fruitful canes are 4 to 6 years old and 1 to 1-1/2 inches in diameter. Bushes should have 15 to 20 percent young canes that are less than 1 inch in diameter, 15 to 20 percent old canes that are 2 inches in diameter and 50 to 70 percent canes that are of intermediate size. Prune the plants when they are dormant (fall to spring). In early spring, you have the advantage of being able to see the canes that were damaged during the winter. There are a number of diseases that can plague our Michigan blueberries and your local extension office can provide you very specific information on each of them.
Now back to your mystery… How old are your plants? Have they ever set flowers or fruited? If not, maybe they need more time. Blueberries are very susceptible to early fall and late spring frosts. What is your soil pH? You can contact your local extension about having a soil test done. Take a good look at the canes. What needs to be pruned? How is your drainage and do your plants get consistent water? Don’t give up! You will likely be rewarded by a little more detective work and patience.