Clinopodium arkansanum aka Limestone Calamint

Clinopodium arkansanum, or limestone calamint, belongs to the mint family. Its native range spans southeastern Canada and the central and eastern United States. It grows in temperate regions, from Ontario south toward Texas. In Missouri, it grows in the Ozarks on limestone glades and bluffs. It also grows on bald knobs, wet meadows, and stream gravel bars. These sites include both dry ground and places with more moisture.

This low perennial forms a dense mat of leaves. Garden plants reach about 1 foot [0.3 m] tall and wide. Rhizomes and creeping runners help the plant spread across the ground. The runners, called stolons, take root where their nodes touch soil. Their leaves range from oval to elliptic in shape. Upright flowering shoots rise above this low layer of growth. These shoots reach 0.7–1 foot [0.2–0.3 m] tall. They bear small, narrow leaves in opposite pairs. The foliage has a scent.

Small, two-lipped flowers range from white to pale purple. Missouri Botanical Garden lists the bloom season as June through July. Chicago Botanic Garden lists later bloom, from July through October. The flowers add color above the low mat of leaves. They also attract butterflies to the planting. The plant's low form suits the front of a border. It also fits rock gardens, open woods, and native plant areas. Gardeners can use it as groundcover or let it naturalize.

Give limestone calamint full sun for best growth. It also tolerates light shade and some poor soils. It prefers neutral to slightly alkaline soil with good drainage. Even moisture suits it, but established plantings can tolerate dry soil. Some plants grow well in the dry ground of limestone glades. It also tolerates shallow, rocky soil. Both gardens list it as hardy in USDA zones 4–8. Missouri Botanical Garden describes it as easy to raise from seed.

This plant needs little routine care. It can spread through runners and by sowing its own seed. Cut it back after bloom to keep the planting neat. This also removes worn foliage and helps limit unwanted seedlings. Missouri Botanical Garden reports no serious insect or disease problems. Deer and rabbits tend to leave it alone.