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Sunday, April 9, 2017

Native flowers for pollinators

More complications in the search to provide habitat and food for pollinators emerged from a fascinating lecture I attended last week organized by Grow Native Massachusetts. Annie S. White spoke about her research comparing pollinator preferences for flowers of native perennials versus “native cultivars.” 

Annie counting pollinators in her test plot

Cultivars are plants that have been deliberately selected or bred for desirable characteristics, such as different flower forms or colors. 

    Annie’s research filled an important gap for gardeners who want to do the best thing for pollinators. When we shop at the garden center, we’re often choosing between cultivars of native plants. For example, purple coneflower, Echinacea purpurea, is so popular that breeders offer dozens of cultivars. 

Are my purple coneflowers the native species or a look-alike cultivar?

Instead of the plain daisy form with deep pink petals, you can have a range of colors and flower forms, going as far as showy (or ugly, depending on your taste) double flowers that don’t look much like the unimproved natives. 

Echinacea 'Summer Flower Pink'--highly modified from the native species

You may not be able to buy the straight species at all. Were we right in assuming that these cultivars were just as valuable to pollinators?

    Annie spent summers standing in her experimental plots counting the pollinators that visited the flowers. Her study of eleven New England native species and their cultivars found that the more the cultivars differed from the native species, the less they offered to pollinators. In the case of purple coneflower, pollinators liked the native flowers best, accepted a white-flowered cultivar with little difficulty, 

A white coneflower cultivar is good enough for this bee

but eschewed a double-flowered variety and a sterile hybrid. 

    Double flowers are often sterile, because stamens have morphed into extra petals. So the pollinators get no pollen from these flowers. No wonder they’re not attracted to them. 

    Annie did a lot of detective work to uncover the origin of the native cultivars she studied. I was surprised that several turned out to be hybrids, or crosses between two species, although they were not labeled as such. 

     To make things more complicated, even seeds may not be accurately labeled. A study of sundial lupine seeds (Lupinus perennis)  recently found that only two out of ten sources were providing the true native species. The rest were seeds of naturally-occurring hybrids between the natives and cultivars that either escaped from cultivation or were intentionally planted along highways. 

Wild Maine lupines have interbred with cultivars

     Interestingly, the majority of Annie’s plants were pollinated by bees, with bumblebees leading the way, honeybees next, and a mix of native bees third. Only two percent were pollinated by butterflies and moths.

     For us amateurs, what’s a reasonable procedure for choosing plants that benefit pollinators? First we have to make sure the plants we buy haven’t been treated with systemic insecticides such as neonicotinoids that kill bees and other pollinators. Then we have to do our best to find native species or cultivars that have been only slightly modified. 

This black-eyed Susan cultivar must be close enough to the native species to attract pollinators

Easier said than done. I hope Annie’s research heralds a new awareness among growers so that in future we’ll be offered plants that are truly pollinator-friendly.


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