Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Northern highbush blueberry bushes can produce berries even when there is no or limited pollen movement by bees. Some of the flowers can turn into berries, even if there are poor pollination conditions or low bee activity during bloom. However, often these berries will be small, slow to ripen, and may drop off early. For maximum potential yield, it is important that the flowers are visited by bees during bloom to transfer sufficient pollen while the flower is still viable so that fertilization can occur, leading to seed set, berry expansion, and larger berries.
In addition, some varieties benefit from cross pollination. Fields should be planted with a combination of varieties that bloom around the same time and that are compatible. For cultivars dependent on having cross-pollination for full yields, this can provide a 10-20% increase in yield from the improved fruit set and berry size.
Flowers of blueberries are generally less attractive to honeybees than other flowers due to the relatively low nectar. Because of this, move bees into blueberry fields after 5% bloom but before 25% percent of full bloom to avoid movement to more preferred flowering plants. Placement near to the blueberry field can also help to keep them focused on the crop.
Research has shown variation across northern highbush cultivars in their needs for bee pollination due to the relative attractiveness of different cultivars and their degree of self-compatibility. Experience shows that a minimum of 2 hives per acre are needed. In some cases, 5 hives per acre are recommended (such as for Jersey and Earliblue). Some growers are using up to 8 colonies per acre to ensure good pollination if spring weather is cool and there are only a few good days for honeybee activity. A rule of thumb is that you’ll need 4 to 8 honeybees per bush in the warmest part of the day during bloom to get blueberries pollinated.
Figure: Honeybee pollinating a blueberry flower.
Bumblebees are very efficient at pollinating blueberry, with activity at lower temperatures than honeybees, faster visits to flowers, and higher rates of pollen transfer per flower visit. A single visit of a bumble bee to a blueberry flower can deposit sufficient pollen to get full pollination, whereas three visits are needed by honeybees.
Blueberry information was adapted from https://bee-health.extension.org/pollinating-highbush-blueberries/