Strawberry Pollination: a Complex and Tricky Business

Of course, a strawberry should taste sweet, but we buy with our eyes before our taste buds. Part of the visual appeal is the bright red coloring. We are also trained to appreciate the typically long, cone-shaped berry. And the shape of the berry is heavily dependent on pollination.

A strawberry flower contains both male and female parts (not unlike many other fruits such as apple). The male components, which ring the outside of the flower, must shed the pollen into the flower center. Here, the 400 or so pistils (female flower part) accept the pollen and fruit will be set. Each small seed on the outside of the berry is the remnant of the female flower. If pollen grains fail to reach each pistil, the fruit becomes disfigured or does not reach its full size. Rarely do we see this in the marketplace as growers would never permit this disfigured product into the stores — poor pollination results in lower marketable yields.

Each individual pistil (female) must be pollinated with a pollen grain (from an anther) from same or nearby flower. Photo: University of Maine Extension

With the flower containing both sexes, pollen should easily move to where it needs to go. Wind and rain can do a pretty good job of getting it scattered throughout the flower. With some varieties, that is all that is needed.

Other varieties need some help, and there is a big role for insect pollination in strawberries. Dr. Heather Grab, of Cornell's Entomology Department, has been looking into the role of pollinators in strawberry production. She has stated that insect pollination can reduce malformations and improve berry size by 40% or more. Also, insect pollination is found to increase sweet flavor, extend the shelf life of fruit, and even reduce the prevalence of grey mold.

Past research has shown that it is not just one pollinator that creates a full, well-developed berry but rather many groups. Some of the smaller, native bees tend to forage at the base of the flower where space is small and tight. Larger bees, such as the bumblebee, can't fit into those spaces and tend to land onto the top of the flower and deposit pollen on those flowers that would be located on the berry tip.

The tarnished plant bug will feed on seeds in developing fruit (that already have been pollinated) which can cause fruit malformation, a similar look to poor pollination. While still edible, it looks unappetizing.

Poorly pollinated berries can be deformed, like insect damage from the tarnished plant bug. Photo: Dr. Heather Grab, Cornell University

If growing strawberries, consider the natural habitats around the farm. While honeybees can be brought in (or a neighbor has them), our outside edges provide a wealth of nesting sites and alternative flowers for foraging.