Trichostema dichotomum aka Bastard Pennyroyal

Trichostema dichotomum, or blue curls, is an annual wildflower. It belongs to the mint family, Lamiaceae. Its native range includes southeastern Canada, the central and eastern United States, and the Bahamas. It grows in dry, open woods and sandy clearings. It also grows near rock outcrops. This plant completes its life cycle in one growing season.

Plants stand 1–3 feet [0.30–0.91 metres] tall and spread 1–2 feet [0.30–0.61 metres]. Their growth rate is moderate, and their form is upright. Fine hairs cover the straight, square stems. The simple green leaves grow in opposite pairs. They have an oval shape and smooth, toothless edges. Hairs also cover the leaves, which can feel slightly sticky. Deep veins give the upper leaf surface a slight crease. Crushed leaves release a lemon scent, but the stems lack scent.

Flowers appear from August to November, with blue, purple, or white blooms. Long, curved stamens give blue curls its name. Each two-lipped flower has four upper lobes and one larger lower lobe. The lower lobe may show white shading and dark spots. Flowers form cymes, which join into a branched panicle. Each cyme holds three to seven flowers. Pairs of leaves surround the cymes and single flowers. Flowers grow smaller toward the top of each cyme. They open early, then shed petals and stamens around midday. Four green nutlets remain after the flowers fall. These turn dark brown as they ripen. Fruit occurs from September through December.

Grow blue curls in full sun with at least six hours of direct light. It suits sandy soil that drains well. NC State lists neutral soil and moist to occasionally dry conditions. Its listed USDA range covers zones 7–11. Grow new plants from seed. A strong plant can form hundreds of flower clusters and many seeds. These seeds can sprout on their own, creating extra work where space is limited.

Blue curls suits native gardens, meadows, borders, and naturalized areas. Gardeners can plant it in small groups or larger masses. Native bees and beetles visit the plant. Its late flowers add color through summer and fall. The plant turns tan in fall and can serve in dried arrangements. NC State reports no insect or disease problems. Its main noted concern is keeping self-sown plants under control. The supplied sources do not establish human edibility or safety for people and pets.