Nierembergia, or cupflower, is a heat-loving, compact mounding plant that is smothered in flowers from early summer through fall. A tender perennial that survives only in zones 7-10, it is easily grown as an annual in colder areas.
The genus Nierembergia (nee-rem-BERG-ee-uh), native to Argentina, is named for Juan Eusebio Nieremberg, a 17th century Spanish Jesuit theologian and naturalist. The taxonomy of this genus (in the potato family or Solanaceae) is rather confused, so the species for cupflower may be listed as caerulea, frutescens, hippomanica or scoparia. It grows neat, spreading mounds about 12-15 inches across. The fine textured foliage is produced on multiple stems, with stiff, linear leaves to 1/2″ long. The one inch white or bluish-purple star-shaped, saucer-like flowers have lemon yellow centers. Their color does not fade even in the brightest sun.
Use Nierembergia for edging, in borders, rock gardens, or containers, including hanging baskets and window boxes. They thrive in this hot environment, spilling out to soften the edges of the stones and hiding the scraggly bases of the other plants.
Start Nierembergia from seed sown indoors 8-10 weeks before your date of average last frost. Barely cover the seed; it should germinate within 2-3 weeks at 70°F. Keep moist until emergence, then the plants can be kept on the dry side. Young plants grow very slowly, but grow more quickly once transplanted. Transplant outdoors 6-12 inches apart (after hardening off) just before last frost date in moist, organically rich, well-drained soil in full sun. Mulch to help retain moisture and keep the soil cool. Plants are drought tolerant once established. Stem cuttings can be taken in late summer to hold the plants over the winter.
There are only a few varieties commonly available:
- ‘Mont Blanc’ is a profuse bloomer with brilliant white flowers on plants only 6 inches high that spread to 12 inches wide. The small cup-shaped flowers face upwards. It was an All-America Selection winner in 1993, and reportedly has better heat tolerance than the species.
- ‘Purple Robe’ has blue-violet flowers. The plants are about 8 inches tall.
– Susan Mahr, University of Wisconsin – Madison