By Elaine Mills, Extension Master Gardener
Photos © Elaine Mills
Gardeners who want to plant more perennials for pollinators will be interested in the results of a 2013 plant trial conducted by Penn State Extension, Bees, Bugs & Blooms. Three species native to our Mid-Atlantic region were ranked among the best plants for flowering longevity, and they also did well in attracting desirable insects.
Clustered mountain-mint (Pycnanthemum muticum), which had the lengthiest period of peak bloom at 10 weeks (July to September), also ranked first for sheer number of insect visitors –78 – during a two-minute period. In subsequent testing, it consistently ranks the best for diversity of pollinators, attracting native bees, beneficial wasps, beetles, skippers, and small butterflies. This plant grows about 1 to 3 feet tall and bears dense, flat-topped clusters of tubular pink flowers in bright shade to sun. Its leaves have a lovely silvery appearance. Like other mints, it can spread to form colonies, but its rhizomes run close to the soil surface, making it easy to control. Deer dislike its aromatic foliage.
Smooth oxeye (Heliopsis helianthoides), an upright, clumping wildflower, also ranked well for length of bloom time. Its 2-inch to 3-inch yellow, daisy-like flowers bloom for most of the summer into early autumn. At 3 feet to 5 feet in height, this plant is best used at the back of garden beds, although its stems can be cut back by as much as one-half in May to reduce its final height. As with mountain-mint, it blooms best in sunny locations, and it is also deer-resistant. This species is highly supportive of wildlife: Its nectar attracts butterflies and native bees, birds consume its seeds, and its stems provide winter cover for beneficial insects.
Swamp milkweed (Aslepias incarnata) also ranked well in the trial for both pollinator diversity and sheer number of insect visitors, and Penn State Extension continues to recommend it highly. This perennial is best known as one of the three locally native milkweeds that serve as host plants for Monarchs, but its nectar also attracts bees, hummingbirds, skippers, and a variety of butterflies. It is a 4- to 6-foot multi-stemmed plant with flat clusters of pink to mauve flowers from June to August. As its name suggests, swamp milkweed prefers moist to wet soil, but it can tolerate some drought once established. Deer seldom severely damage it.
All these plants can be found in the Extension Master Gardener demonstration garden at the Glencarlyn Library in Arlington. Smooth oxeye is planted in the newly renovated Pollinator Garden, and clustered mountain-mint is one of two mints located in large adjacent containers. There is a tall stand of swamp milkweed next to the blackberry plant growing on the fence bordering the Children’s Garden.