The genus Lobelia belongs to the Campanulaceae—or bellflower family—and comprises more than 360 species that are either half hardy annuals or perennials. According to the South African National Biodiversity Institute, this cosmopolitan species thrives in tropical and subtropical areas. This herb features angled and branched stems and flowers with five petals.
Lobelia as an annual, such as edging lobelia (Lobelia erinus), reaches a height of 4 to 12 inches. As an edging plant, the species works well for rock gardens. Cascading flowers feature tiny purple, blue or white petals. Blooming begins early in spring to fall.
Perennials such as cardinal flower—Lobelia cardinalis L.—grow to about 1 to 6 feet high. Dark green, deciduous leaves have autumn foliage. Aromatic cardinal flowers befit a perennial garden. Bloom time runs from May to October. Other perennials feature tiny blue, violet blue or yellow spiky flowers. The oval-shaped fruit contains small seeds.
Native to North America, habitat of the lobelia includes sheltered to exposed rocky slopes, coastal mountain slopes, dry grasslands, pastures, fallow land, clearings, woodland floors and edges of forests. As a weed, lobelia grows along roadsides, ditches or marshes.
Lobelia prefers moist, humus-rich, heavy clay soil. Other soil types include loam and sand. Optimal pH is slight acidity between 6.0 and 7.5. Light exposure includes sunny or part shade, such as the understory of woodlands.
Propagation of lobelia occurs by seed or division of clumps in spring. Perennial seeds benefit from a refrigeration period of about three months. Place seeds with soil in a black bag. Sow stocked seeds indoors on vermiculite or prepared seed beds. Seeds should stay in a moist layer for seven or eight weeks at 40 Fahrenheit. Germination occurs in about two to three weeks. To avoid rotting, water the seedling from below.
After the final spring frost, transplant seedlings when very small. For small lobelia, spacing can be about three inches apart. For larger lobelia, spacing may be two feet apart. With a low tolerance of drought, lobelia requires regular watering to keep the soil moist, especially in dry periods. Seed capsules open as seeds mature. Seeds collected in a sealed refrigerated container can store well for up to three years.
Pollinators—organisms that transfer pollen grains from the male reproduction organ or anther to the female pistil—include a variety of bees, butterflies and birds. Ruby-throated hummingbirds and hummingbird flower mites also consume lobelia pollen and nectar.