Diggin’ In: Field thistles an underappreciated addition for home gardens

August 24, 2015

Field thistle is not the kind of plant you usually find in a home garden.

Yet maybe it should.

"Field thistle is very attractive to goldfinches, hummingbirds and clearwing moths," says native plant expert Helen Hamilton of Williamsburg, Va. She is past president of the John Clayton Chapter, Virginia Native Plant Society, and co-author of "Wildflowers and Grasses of Virginia’s Coastal Plain."

Scientifically called Cirsium discolor, the prickly plant with deep-cut leaves is a biennial (lasting two years), forming only a low rosette of spiny leaves, according to Hamilton. After the first year, the plant grows three to eight inches tall, on light green, hairy stems without spines. Spiny leaves alternate on the stem, green on the upper side and white underneath. Cirsium discolor is sold by Prairie Moon nursery at .

Rose-purple flower heads appear at the ends of stems August through November. The base of the flower head is roundish and covered with bracts that look like fish scales. The golden tint to the flower-head base is one of the distinguishing characteristics of the three common thistles.

Two other species of thistles are common, Hamilton says. Blooming June through November, the introduced bull thistle (C. vulgare, native to Europe) has a very prickly rose-purple flower head, and the stem is winged with spines. The other native, yellow thistle (C. horridulum), blooms earlier, March through June with a yellow flower head.

Thistles are asters, but there are no rays, only disk flowers, Hamilton explains. Many Aster family members, like sunflowers and daisies, have both ray and disk flowers. Birds and insects seek nectar by poking their bills or proboscises around the tubular ray flowers. Look closely at these flower heads, to see the style (female reproductive part) emerging from the surrounding cylinder of anthers.

Field thistle grows wild in nearly every county in Virginia, in roadsides, fields, meadows and ranges from Quebec west to Manitoba, south to North Carolina, Mississippi, Louisiana and Kansas.

"This is an easy plant to grow, preferring full sun in loamy soils," she says.

"It does well in the back of the perennial bed or in a meadow. Since it blooms so late in the year, the masses of the pink flowers covered with visiting goldfinches furnish lots of color to the fall landscape. Goldfinches eat the seeds and line their nests with the ‘thistledown,’ tufts of hair on the seeds that serve as parachutes."

Field thistle is the host plant for the painted lady butterfly — its caterpillars feed on the foliage. Many bees are important pollinators for the flowers, and one is a specialist — the thistle long-horned bee (Melissodes desponsa) only visits members of the Cirsium genus.

The painted lady is found on every continent during some part of the year, except South America, according to Hamilton. In North America, they probably spend winter in Mexico.

"They live almost everywhere, especially meadows, parks and gardens," she says.

"In our area (in Virginia), males perch on bare ground in open areas. After mating, females lay eggs on the tops of host plant leaves, and the caterpillars live in silk nests on the leaves."

Painted lady is also known as the thistle butterfly, since native thistles are the favorite food of the caterpillars. Other host plants include hollyhock, mallow and various legumes. The adults feed on nectar from plants three to six feet tall, especially thistles, but also asters, cosmos, blazing star, ironweed and joe-pye-weed.

Painted lady butterflies are similar to the American lady (Vanessa virginiensis). Brian Taber, of the Coastal Virginia Wildlife Observatory, says that painted lady is not as common.

There are some subtle differences on the tops of the wings, he says, "but the best distinguishing feature is that there are two large eyespots on the hindwing below for the American and four small eyespots there for the painted."



McClatchy-Tribune Information Services