Begonias, impatiens, and other popular annual flowers can draw in pollinators— but only if you pick the right cultivars
Annapolis, MD; May 13, 2024, Entomological Society of America—While wildflowers and perennials are a must for supporting pollinators, there’s no denying the popularity of many annual flowers for their colorful, visual appeal. Annuals are often thought of as pollinator “deserts,” but a new study suggests choosing the right varieties can give annual flowers a role in nourishing bees and other pollinating insects in home gardens.
In a two-year study, researchers at Michigan State University observed pollinators visiting 25 different varieties, or cultivars, of the six most popular annual flower species in the United States, finding significant variation in apparent pollinator attractiveness between cultivars, even within the same flower species. Two begonia cultivars, “Cocktail Brandy” and “Ambassador Rose Blush,” and the impatiens cultivar “Accent Coral” drew in the most pollinating insects among all those tested. Results of the study are published in the Entomological Society of America’s Journal of Economic Entomology.
“For homeowners and other customers of garden centers, it means that they can choose cultivars of some of their favorite flowers that provide some support for pollinators,” says David Smitley, Ph.D., professor emeritus in the Department of Entomology at Michigan State University (MSU), and lead author of the study.
Popular among people, but what about pollinators?
Among all flowering plants sold at garden centers in the United States every year, more than half are annual flowers, totaling nearly $2 billion in sales value in 2020, according to data from the U.S. Department of Agriculture. Nearly half of those sales—more than $900 million—are from the top six annuals: petunias, geraniums, pansies, begonias, impatiens, and New Guinea impatiens. (This group made up six of the top seven annuals in the United Kingdom in 2021, as well.) These were the flowers Smitley and colleagues chose to study, driven by a lack of previous experimental research on pollinator attraction to them.
To begin to fill this knowledge gap, the team chose three to five cultivars of each of the six annual flower species, for a total of 25 cultivars, to evaluate alongside four other benchmark flower species known to be attractive to pollinators. Smitley and MSU colleagues Colin Oniel, Erica Hotchkiss, and Erik Runkle grew six groups of the annuals (150 plants in total) in mixed plots at a horticultural facility at MSU in the summer of 2017 and again in 2018, with the benchmark species nearby. From early June to late August, the researchers visited the plots regularly to collect insects on the flowers, recording which cultivars they were visiting.
With help from bee taxonomist Jason Gibbs, Ph.D., at the University of Manitoba, and statistician Jared Studyvin, Ph.D., at the University of Wyoming, the team then identified the insects to genus or species and analyzed the visitation rates to the flowers, comparing results between flower species, between cultivars within each species, and against visits to the known pollinator-friendly benchmark flowers.
Smitley says he was surprised by the results, which showed significant variation in pollinator visitation among cultivars of the same flower species and that some cultivars were attractive enough to warrant choosing for supporting pollinators in home gardens.
Variation in the varieties
Overall, pollinator visits to annual flowers were low compared to the benchmark flowers in the study. This was as expected—wildflowers and perennials maintain their strong appeal to pollinators because their nectar and pollen production hasn’t been bred out of them in favor of flower appearance. But even among the annual cultivars, some showed “modest” attractiveness to pollinators, and much more than other cultivars.
For instance, the begonia cultivars “Cocktail Brandy” and “Ambassador Rose Blush” attracted pollinators at more than triple the rate of the lowest tested begonia cultivar. The impatiens cultivar “Accent Coral” was…
