Zinnia grandiflora aka Rocky Mountain Zinnia

Zinnia grandiflora belongs to the daisy family, Asteraceae. Gardeners call it plains zinnia or Rocky Mountain zinnia. Its native range spans the central and west-central United States into Mexico. U.S. records include Arizona, Colorado, Kansas, New Mexico, Oklahoma, and Texas. It grows in dry ground with sand, loam, or gravel. These sites often have a limestone base. Sources describe it as a perennial that can also grow as an annual.

This small plant forms a dense, rounded mound. It grows about 0.33–0.67 feet (0.10–0.20 metres) tall and wide. Its growth rate is slow. Many green stems branch from a woody base. This gives the plant a small, shrub-like form. The stems have no scent. Narrow green leaves grow in opposite pairs along them. The leaves look like short needles and lack hairs. When flowers fade, the foliage still forms a low green mat.

Yellow flower heads bloom from May through October. The flower description gives their width as about 0.08 feet (0.025 metres). A broader size listing allows larger heads. Deep yellow rays surround an orange-brown centre. The long season adds colour through summer and into fall. Bees, moths, and butterflies visit the flowers. The fruit is an achene. The plant spreads by rhizomes, which help it cover bare ground.

Give plains zinnia full sun and soil that drains well. It also accepts some shade, but cannot cope with wet ground. It tolerates drought, heat, strong wind, and cold. NCSU lists it for USDA zones 4–8. Sand, shallow rocky soil, and well-drained clay can suit it. Hot driveways and south-facing slopes are useful planting sites. Steady moisture can make the plant fuller and its blooms brighter. This does not remove its need for good drainage.

Use it in borders, rock gardens, containers, or pollinator gardens. Its spreading roots can help hold soil on sandy or steep slopes. It needs little upkeep and resists deer and rabbits. NCSU reports no major problems, but also links southern blight and bacterial wilt. Propagation options include seed, division, and stem or root cuttings. Divide plants or take cuttings in spring. Seed can be hard to obtain because cleaning may break it. NCSU lists it as non-toxic to cats, dogs, and horses. The supplied sources give no evidence of edible parts.