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Diggin’ In: Ragwort’s tiny yellow flower adds color in shady, swampy areas

April 11, 2016

Along with daffodils, golden ragwort welcomes spring with bright yellow flowers covering swampy areas now until early summer, according to native plant expert Helen Hamilton.

Known scientifically as Packera aurea, the native perennial grows one to three feet tall, with only a few deeply-cut leaves on the stems. Leaves at the base of the plant are heart-shaped, and form a large rosette.

"After the flowers fade, the leaves spread to form a nice groundcover that persists over most of winter," says Hamilton, past president of the John Clayton Chapter, Virginia Native Plant Society, and retired biology teacher living in Williamsburg, Va. Learn more about the native plant society at www.vnps.org.

Ragwort grows naturally in bogs, wet woods, floodplains and meadows in eastern North America, Hamilton continues. The plant thrives in full shade with acid, rich soil, in zones 3-9. It spreads easily by seed and underground roots, forming large attractive colonies.

"Ragwort grows under trees where nothing else will thrive," she says.

"In a home-based woodland garden or a perennial border in the shade the masses of golden yellow look wonderful with bluestar (Amsonia tabernaemontana) and red columbine (Aquilegia canadensis). Deer also avoid golden ragwort because the leaves contain toxic chemicals."

Hungry small bees and flies emerging from winter frequently feed on ragwort, and carry its pollen to nearby flowers. Those feeding insects include green metallic sweat bees.

Beneficial sweat bees

Some bees in the Halicitid group are attracted to the water and salt in human perspiration — thus their nickname, "sweat bees."

"They usually do not sting, unless disturbed, and the sting is minor, like a tiny pinprick," says Hamilton.

These are very small bees, less than half-inch long, and are usually overlooked because most have drab brown or gray bodies, she adds. Some species, however, have vivid, shiny green bodies that are easy to spot.

"These metallic green bees are most visible collecting pollen and feeding on nectar in the disk flowers of the Aster family, which includes golden ragwort, and on goldenrods."

Sweat bees are found worldwide, and are particularly abundant in North America, with 45 species in Virginia, ranging from brilliant green to dull brown in body color, continues Hamilton.

"They are everywhere — in backyard gardens, open fields and parks," she says.

"It’s impossible to over-estimate the importance of these very small bees — they are responsible for most of our familiar summer flowering plants. Without their activity, feeding on nectar and collecting pollen, most flowers would never set seed for the next generation. These bees are generalists, visiting a variety of flowering species, and collecting pollen in baskets or in bristles all over their bodies."

The metallic green bees are in the genus Agapostemon, represented by 14 species in the eastern United States, according to Hamilton.

"Like bumblebees, sweat bees do ‘buzz pollination,’" says Hamilton.

"By rapidly moving flight muscles, disconnected from their wings, they generate sonic vibrations that cause pollen to be released from some plants, like tomatoes and blueberries."

Sweat bees are more numerous than most bees, except for the non-native honeybee, and although they do not produce honey, their services as pollinators of garden flowers, fruits and vegetables are immeasurable, Hamilton adds.

To encourage populations of sweat bees, leave patches of bare soil for nesting habitat, and plant lots of different wildflowers, especially those with long blooming periods, from early spring through fall such as wild petunia, blue vervain, Maryland golden aster, summer phlox and Joe pye-weed.

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