Santa Fe Botanical Garden

Common name: Hartweg's sundrops, western sundrops

Family: Onagraceae (Evening Primrose)

Synonym: Calylophus hartwegii

Distribution: Central and Southwestern United States, Northern Mexico

Habitat: Prairies, plains, pastures

Hardiness: USDA Zone 5 (-20 to -10 °F)

Life form: Herbaceous perennial

Occurrence in New Mexico: New Mexico native plant

Growing Conditions: Hartweg’s sundrops grows in prairies, plains, meadows, and pastures from Wyoming and Nebraska, south to Arizona and Texas, and into Mexico. It is not particular about soil type and will grow in loam, sand, and limestone or caliche type soils. It prefers well draining soils, but will tolerate clay. It thrives in heat and does well on rocky slopes and rock gardens. It does well in full sun or partial shade. It flowers best if given regular water when planted in full sun, but is very drought tolerant. Deadheading will prolong the flowering. It dies back in winter and re-sprouts in spring; cut back during dormancy to improve appearance. Hartweg’s sundrops is propagated by seeds, but is difficult to germinate. Sow in fall, stratify for 1-3 months before sowing in spring, or scarify seeds before sowing.

Description: Hartweg’s sundrops is a bushy plant, 12-18 inches tall and 24 inches wide. The stems are upright or drooping, usually branched, and become woody with age. The leaves are smooth, linear or lance-shaped, up to 2 inches long and less than ½ inch wide. Clusters of small leaves often grow in the axils of the stem leaves. Blooms emerge from the upper leaf axils in spring and summer, with cup-shaped flowers that open in the evening and close by the next afternoon. Each 2-inch wide flower has 4 yellow petals that dry to a pinkish color, red-spotted sepals, and 8 stamens surrounding a flat, 4-sided stigma. At the base of the flower, the petals and sepals are fused to form a ½-2½ inch long floral tube (hypanthium). Flowers develop into cylindrical seed capsules up to 1½ inch long. Plants spread by rhizomes and by reseeding.