Background
As a fruit-producing plant, the cranberry requires pollination of its blossoms. Without pollination, no fruit will form. The cranberry flower’s main pollinator is the bee. On commercial bogs, honey bees – originally imported to North America from Europe in the 1600’s – are typically the primary pollinator. Two honey bee hives (the equivalent of up to 80,000 bees) are required for every acre of cranberries. Hives are rented and usually arrive at the marsh in mid-late June. As a rule of thumb bees should arrive when 10% of the cranberry blossoms have opened. The honeybees forage for nectar, which they convert to honey. They also seek pollen, which supplies their protein needs. As bees visit blossoms, their bodies brush against flower parts, picking up and dropping off pollen. In this way, their foraging results in pollinated blossoms. These bees are sensitive to adverse weather conditions and will not visit the plant during a rainstorm or high wind.
Unlike the honey bee, the bumblebee is native to America and served as the original cranberry pollinator. The bumblebee is a very efficient pollinator but, because the colony is considerably smaller than the honey bee colony (200-300 bees per hive) it is used as a supplemental pollinator. Less impacted by poor weather conditions, the bumblebee will pollinate in the rain.
Although honey and bumble bees are critical to cranberry pollination, it is nonetheless very important that the grower not keep the bees on the marsh too long. Once the peak cranberry bloom has passed, bees will move on to visit and pollinate other plants, including flowers of the elderberry, sumac, and goldenrod. This lesson includes a graph that illustrates this idea. It’s important to note that, as a simplified model, it does not necessarily correlate to specific weeds and specific dates. Instead the graph has been kept simple so that students can grasp the main idea.