Over the last few days I was attending an annual horticultural trade show in Columbus, Ohio. I met up with some colleagues at The Cincinnati Zoo and Botanical Garden, which has spearheaded a program — Pollinator Watch — to observe and document plant and pollinator interactions.
Each year they evaluate hundreds of trees, shrubs, perennials and some annuals to understand the best plants for attracting the broadest number of species of pollinators. This article will highlight their “best of the best” in 2023.
The following are some of the top-ranked perennials for pollinator abundance, which was “measured by counting insects within a 1.5 square feet section of the plant for 10 seconds. In order to qualify, plants had to be observed at least four times during the bloom season.”
The rattlesnake master, Eryngium yuccifolium, was the top-ranked perennial, native to most of the states in the southeastern U.S. and the Midwest, occurring as far west as Nebraska, Kansas, Oklahoma, and Texas. In the summer, the stems are covered in thimble-like white flowers. “Yuccifolium” suggests the yucca-like foliage that forms at the base. In the garden, it will seed serendipitously throughout the garden. Unwanted seedlings can simply be weeded out.
Eryngium leavenworthii is a closely related native annual noted for being a magnet to pollinators and having iridescent blue-purple flowers. It is native to Texas, Arkansas, Oklahoma, Missouri, and Kansas.
While not native, there are several selections of the perennial onion that are top pollinator attracting plants.
They are characterized by a mounding tuft of bright green foliage. In the summer, stems are covered in globe-like clusters of pink flowers that are born in profusion. Like all other members of the onion family, they are truly deer resistant. Top cultivars included Allium “Millenium,” Summer Peek-a-Boo “Lavender Bubbles,” “Serendipity,” and “Summer Beauty.”
Also, excellent for deer resistance are the hyssops, Agastache. Reaching about 3 feet tall, these mint relatives are covered in spikes of blue to purple flowers in the summer. Agastache “Blue Fortune” was top ranked for attracting pollinators. In the garden, it has great “flower power” and combines well with Echinacea, coneflower; betony, Stachys “Hummelo” and the various mountain mints, Pycnanthemum. “Purple Haze,” “Little Adder,” and “Black Adder” also ranked high.
Considered one of the very best native perennials for attracting pollinators is the mountain mint, Pycnanthemum muticum. While it is a spearmint and peppermint relative, it is by no means as aggressive and invasive in the garden. However, it can quickly form a mass. Reaching 2.5 feet tall, the green foliage supports attractive white bracts in the summer. Amongst the bracts are tiny lavender flowers that allure a myriad of native bees, flies, wasps and other pollinators. Because of the mint-like fragrant foliage it has proven to be completely deer resistant.
Several native hydrangeas were top ranked including the smooth hydrangea, Hydrangea arobrescens “Haas Halo,” considered by many to be one of the “best of the best” of all pollinator plants. And, two selections of the oakleaf hydrangea, Hydrangea quercifolia performed well, including the diminutive “Pee Wee” and another compact form, “Sikes Dwarf.” The oakleaf hydrangeas are noted for their red oak-like leaves which turn shades of purple and red in the fall and for the abundance of cone-like white flowers that cover the shrubs from June into July.
At the end of their pollinator study, they included some helpful tips for attracting pollinators. Sunny conditions are good for pollinators. Planting a diversity of plants will aid in a diversity of pollinators. By planting certain native plants, specific native pollinators that have co-evolved with that plant will be present. Install a water source for pollinators, such as a bird bath. Let your garden stand for the winter. Insects lay eggs in stems of perennials and in fallen leaves. And, every year, if possible, shrink your lawn which will provide more pollinator habitat.
Andrew Bunting is vice president of horticulture at the Pennsylvania Horticultural Society and vice president of the Swarthmore Horticultural Society.
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