Tender perennial that is winter hardy to USDA Zones 7-10. In St. Louis, it is grown as an annual in moist, organically rich, well-drained soils in full sun to part shade. Soils should be kept uniformly moist. Best bloom occurs in cool summer climates. Flowering may slow down considerably in the heat of a St. Louis summer where part afternoon shade is best. A summer mulch retains moisture and helps keep soils cool. Sow seeds directly in the garden 1-2 weeks before last frost date or indoors 6-8 weeks earlier. Set out seedlings or purchased plants just before last frost date. Pinch young plants to promote bushiness. Deadhead spent blooms to encourage additional bloom. If flowering significantly decreases in the heat of the summer, cut back plants to encourage later bloom. If sited in a sheltered location with a southern exposure, plants may survive a mild St. Louis winter. Cuttings may be taken in late summer for overwintering.
Nierembergia scoparia, commonly called cupflower or tall cupflower, is a shrubby tender perennial that grows in a dense spreading mound to 12-30” tall. Cup-shaped, pale blue flowers (to 1” wide) cover the plant with bloom from early summer to fall. Finely-cut, stiff, linear to spathulate leaves to 3/4” long. Stems of this plant branch out to form a shrubby mass of foliage. The Royal Horticultural Society currently considers this species to include the formerly recognized N. frutescens.
Genus name honors 17th century Spanish Jesuit professor of natural history and author Juan Eusebio Nieremberg (1595-1658).
Specific epithet means broom-like.
‘Purple Robe’ is a compact, violet-blue-flowered cupflower cultivar that grows to 6” tall and spreads along the ground to 12” wide. ‘Purple Robe’ has been listed and sold as a cultivar of several different Nierembergia species.
No serious insect or disease problems. Susceptible to tobacco mosaic virus. Watch for slugs and snails.
Bedding and edging. Beds, mixed borders, rock gardens or along walks. Containers, hanging baskets and window boxes.