Nierembergia linariifolia aka Blue Cup Flower

Nierembergia linariifolia is known as cupflower or blue cups. It belongs to the nightshade family, Solanaceae. Its native range runs from south-central Bolivia into southern Brazil and northern Argentina. It grows in a subtropical climate in the wild. This tender perennial often serves as a summer annual. Kew classes its growth form as a subshrub.

Plants form small clumps with upright, branching stems. The foliage also makes a spreading mound with a fine texture. RHS describes plants about 0.7 feet (0.2 metres) tall. Its broader garden range reaches 1.6 feet (0.5 metres) in height and spread. Plants grow fast and reach full size within one to two years. The small, pointed leaves are simple and fall seasonally. RHS describes soft hairs on the stems. The leaves give the mound a fern-like look.

The flowers form open cups with yellow centres. Their colour ranges from light blue to violet and purple-blue. They cover the plant through summer, making flowers its main garden feature. Missouri Botanical Garden gives the bloom season as May until frost. These low plants suit beds, border edges, and paths. They also fit rock gardens and small planting spaces. Pots, hanging baskets, and window boxes offer other ways to grow them. Gardeners can use them as ground cover or plant them in groups. Deer tend to leave them alone.

Grow cupflower in sun, though it also accepts part shade. Choose a sheltered spot with rich soil that drains well. Keep the soil moist rather than letting it dry out. It accepts sand, loam, clay, and chalk soils. RHS also lists tolerance of acid, neutral, and alkaline soil. Its UK hardiness rating is H3, for mild or coastal sites. Missouri Botanical Garden lists USDA zones 7–10. NC State gives the warmer range of zones 8–11. In colder places, gardeners grow it as an annual.

Routine pruning is not needed, but the plant needs some care. Slugs and snails may damage it, and virus diseases can occur. Missouri Botanical Garden names tobacco mosaic virus as a risk. It otherwise reports no serious insect or disease problems. Seed offers a way to raise new plants. Start seed indoors eight to ten weeks before the last frost. NC State also lists direct outdoor sowing in spring or fall.