Pollination of Blueberry Plants

Blueberry Flowers

• Each year, blueberry plants produce clusters of small flowers at the end of plant stems. These bell-shaped flowers, with white, pink or greenish petals, hang open-end down. Each flower contains 10 male stamens, encompassing pollen-bearing anthers, surrounding a single long female style. The ovary is contained at the base of the style. Due to the bell form of the flowers and the general stickiness of the pollen, wind does not effectively pollinate blueberries.

Insect Pollinators

• Major insect pollinators include bees, moths, flies, butterflies and beetles. Of this list, bees are most responsible for blueberry pollination. Some research suggests that honeybees alone account for about 80 percent of the insect pollination of agricultural crops today. There is good reason for this. Honeybees live in large colonies that consist of tens of thousands of bees. These colonies are easily managed and moved around crops. Commercial blueberry operations require supplemental hives of honeybees because there are not sufficient quantities of naturally solitary native bees available for pollination.

Bee Density and Distribution

• Two honeybee hives per acre is generally sufficient in small, isolated blueberry fields. If there are surrounding fields of potentially competing flower species, up to three hives per acre is recommended. Within large commercial field operations, three to five hives per acre is fairly standard. Blueberry flowers within 100 yards of bee colonies will experience the highest levels of pollination. Consequently, proper hive distribution is necessary to ensure consistent levels of fertilization throughout a field. Ideally, colonies should be placed approximately 500 feet apart from one another in all directions.

Pollination Assessment

• Most flowers are fertilized within three days of their opening. They must be fertilized within a week of opening if fruit set is to occur. Flowers become brown and unattractive immediately following fertilization. The overall plant should appear less flowery and more green. The ovary of each flower matures into a berry approximately two or three months after flowering.

Considerations

• Successful harvests depend on weather conditions, climate, disease, weed as well as insect pollinator prevalence. Failure to produce ample crops, however, is often the result of poor pollination. Currently there are no accurate means of predicting native bee behavior. Population numbers may vary significantly each year. In general, the presence of native bees has dramatically declined in the past few decades, due to pesticide use, habitat loss and population fragmentation. As a result, blueberry growers have become increasingly reliant on managed honeybees for pollination.