This week Iowa State University Extension garden experts respond to common questions related to growing and caring for blueberries. Gardeners with additional questions can contact the experts by emailing or calling the ISU Extension horticulture hotline at firstname.lastname@example.org or 515-294-3108.
Blueberries can be grown successfully in Iowa. However, they do have special growing requirements.
Blueberry plants require a sunny location and a well-drained soil high in organic matter. Avoid wet, poorly drained sites. Blueberries are susceptible to root rots in poorly drained soils.
Soil pH also is important. Blueberries require acid soils with a pH of 4.0 to 5.5. Since the pH of most Iowa soils is above this range, the soil pH must be lowered to successfully grow blueberries.
Home gardeners can lower their soil pH by adding sphagnum peat moss to the soil. Sulfur also can be used to acidify the soil. Sulfur should be incorporated into the soil a year before planting, as it reacts slowly with the soil. Aluminum sulfate should not be used to acidify the soil, as large amounts of this material can be toxic to blueberry plants.
When using sphagnum peat moss to acidify the soil, dig a wide, shallow hole. Set the plant at the same depth it grew in the nursery, then backfill with a 50:50 mixture of soil and moist peat (moisten dry peat before mixing with soil).
Highbush and half-high blueberries can be successfully grown in Iowa.
Highbush blueberries perform best in central and southern Iowa. Plants develop into 6- to 8-foot-tall shrubs. Suggested varieties for gardeners in central and southern Iowa include ‘Patriot,’ ‘Blueray,’ ‘Bluejay,’ ‘Bluecrop,’ ‘Rubel,’ ‘Jersey’ and ‘Elliott.’
Half-high blueberries possess greater cold hardiness and are the best choice for gardeners in northern Iowa. Plants are relatively small (varieties commonly grow 2 to 3 feet tall) and produce small to medium-size berries. Suggested varieties are ‘Northblue,’ ‘Northcountry,’ ‘Northsky’ and ‘St. Cloud.’
Plant two or three blueberry varieties to ensure good pollination and maximum fruit set.
Blueberry plants should not be allowed to bear fruit the first two years after planting. Any blossoms that form should be removed. Removal of the flowers maximizes vegetative growth and increases yields in later years. Blueberry plants should come into full production by the fifth or sixth year. Gardeners can expect to harvest five to 10 pounds of fruit per plant from mature highbush blueberries. Half-high blueberries generally produce two to three pounds per plant.
Established blueberry plants can be fertilized with an acid-producing fertilizer, such as ammonium sulfate, in early spring. Apply one-half to one pound of ammonium sulfate per 100 square feet of garden area. Ammonium sulfate supplies nitrogen to the plants and also helps to maintain soil acidity.
Blueberries have shallow, fibrous root systems. Plants quickly become stressed during hot, dry weather. To help retain moisture and control weeds, apply 2 to 4 inches of mulch around blueberry plants. Sawdust, wood chips, pine needles and shredded leaves are excellent mulching materials. During dry weather, water plants every seven to 10 days.
Phytophthora root rot can be a serious problem in poorly drained sites. Phytophthora root rot can be avoided by planting blueberries in well-drained soils. Outside of root rots, blueberries generally have few insect and disease problems in Iowa.
Birds can be a problem as they may devour much of the crop. While scare devices may be helpful, netting is the most effective way to protect the fruit from birds. Netting should be placed over the plants when the fruit begin to turn color. Hang the netting over some type of support structure with the bottom edges of the netting buried or anchored to the ground.