Cirsium horridulum aka Bristly Thistle

Cirsium horridulum is a spiny herb in the daisy family, Asteraceae. Its common names include purple thistle and yellow thistle. Its native range runs from the eastern United States to Honduras, including the Bahamas. In the United States, it grows from southern Maine to Florida and west to Texas. It lives in fields, savannas, roadsides, and other disturbed ground. It also grows along shores and salt-marsh edges. Plants may be annuals, biennials, or short-lived perennials.

Plants usually reach 2–5.5 feet [0.6–1.7 metres] tall. Some reach 8 feet [2.4 metres]. Growth proceeds at a moderate pace. Upright green stems branch and have a winged look. Hairs and many sharp spines cover them. The plant forms a basal rosette of deeply lobed leaves. These measure about 0.7–2 feet [0.2–0.6 metres] long. Smaller leaves grow alternately along the stems. Their edges bear spines, and white woolly hairs cover their undersides. The foliage is green and deciduous, with a coarse texture.

Flower heads top the branched stems from May through August. They reach about 0.25 feet [0.08 metres] across. Each head holds disc flowers within a ring of spiny bracts. Flower colors include pink, purple, yellow, and white. Their nectar draws pollinators, and hummingbirds also visit the flowers. Each small, flat brown achene holds one seed. A feathery pappus helps the wind carry the seeds. Birds eat the oil-rich seeds and gather their tufts for nests.

Choose an open site with full sun for cultivation. The plant also tolerates some shade. It accepts many soil types but grows best in sand. Good drainage suits it, with conditions ranging from dry to moist. Established plants withstand spells of drought. Despite its coastal habitats, it fares poorly in salt or brackish water. NC State lists it for USDA zones 5–10. Sow seeds in fall or early spring. Leave them uncovered, since light helps them germinate. Keep the seedbed moist until seedlings emerge.

This thistle suits meadows, naturalized sites, and butterfly gardens. It hosts little metalmark and painted lady butterfly larvae. Native bees use its dead, hollow stems as nest sites. Cut dead stems to 1–2 feet [0.3–0.6 metres] and leave them standing for bees. Allow those stems to break down in place. Plants need little upkeep and have no major reported pest or disease problems. Their spines discourage deer and rabbits but can hinder garden work. Plants may spread into lawns and flower beds, so place them with care.