Common Name: lobelia
Type: Herbaceous perennial
Native Range: Southern Africa
Zone: 10 to 11
Height: 0.50 to 0.75 feet
Spread: 0.50 to 1.00 feet
Bloom Time: April to June
Bloom Description: Blue to violet with yellow to white throat
Sun: Full sun to part shade
Suggested Use: Annual
Tender perennial that is winter hardy to USDA Zones 10-11. In St. Louis, it is grown as an annual. It is best grown in organically rich, evenly moist, well-drained soils in full sun to part shade. In St. Louis, plants are best sited in part shade. If grown from seed, start indoors 8-10 weeks before last frost date. Can be difficult from seed, however, and many gardeners simply purchase plants in cell/six packs from local nurseries each spring. Appreciates regular fertilization (every 2 weeks) throughout the growing season. Best bloom is in late spring to early summer. Like pansies and linaria, these plants perform beautifully in cool spring weather, but begin to rebel at the onset of hot and humid summer weather. In the event foliage and flowering significantly declines in summer, consider cutting back plants to encourage a fall bloom or simply removing them from the garden.
Lobelia erinus, commonly called edging lobelia, is noted for its profuse bloom of intensely colored flowers. It comes in both upright and trailing varieties, typically growing to 4-9” tall. Loose clusters (racemes) of two-lipped, tubular flowers (to ½” across) bloom throughout the growing season in cool climates, but often decline significantly in St. Louis summers. Flowers have large, fan-shaped lower lips characteristic of the lobelias. Cultivars feature many different flower colors, including blue, violet, purple, red and pink, often with yellow or white eyes. Narrow, linear, serrate stem leaves (to ½” long) may be flushed with bronze. Flowers are attractive to butterflies.
Genus name honors Matthias de l'Obel (1538-1616), French physician and botanist, who with Pierre Pena wrote Stirpium Adversaria Nova (1570) which detailed a new plant classification system based upon leaves.
No serious insect or disease problems. Mid-summer die back is usually the most serious problem.
Trailing forms are best used in hanging baskets, containers or window boxes which enable the flowering stems to cascade downward over the sides. In mixed basket/container plantings, stems can also be easily removed as they succumb to hot summer weather. Upright varieties are best for edging and bedding. A good plant for rock gardens or butterfly gardens.