Lobelia siphilitica, also known as a great blue lobelia, is a herbaceous, short-lived perennial in the Campanulaceae, or bellflower, family. It is native to the central and eastern parts of the U.S. and Canada. This plant tolerates very cold temperatures and can live in water-logged soil. Gardeners may use great blue lobelia in bedding or containers. The plant is fairly easy to grow and to propagate. Some Native American tribes used this plant medicinally.
This species grows best in U.S. Department of Agriculture Hardiness Zones 3-9 and can tolerate temperatures as low as -40° Fahrenheit (-39.9° Celsius). Great blue lobelia prefers full sun or light shade. The plant has high water needs and grows well in areas where the soil does not dry out completely including bogs and swamps. It prefers soil with a pH level between 6.1-7.5, or mildly acidic to neutral.
The herb may grow to a height of 24-36 inches (60-90 cm). From August through October, the great blue lobelia produces spikes of blue, irregularly shaped, two-lipped blooms. Each serrated leaf grows to be 3 to 5 inches (8-12 cm) long.
Gardeners and landscapers may use these plants areas that are continually wet. The plants may also be used in wildflower or container gardens. Hummingbirds, bees, and butterflies are attracted to great blue lobelia. The plant relies on these birds and insects for pollination because it cannot self-pollinate.
Propagation of the great blue lobelia is done using seeds, taking cuttings, or by dividing clumps of mature plants. Seedlings can be started inside and transplanted outdoors 8-10 weeks following germination. When planting in a garden bed, they should be spaced between 18-24 inches (45-60 cm) apart.
To propagate using cuttings, two node stem cuttings 4 to 6 inches (10.6-15.2 cm) long may be taken before the plant blooms. The cut ends must be treated with a rooting hormone and then placed in a mixture of sand and perlite. If the cuttings are covered lightly, given plenty of light, and kept moist, the roots should sprout in two to three weeks. Clumps of well-established plants can be divided either in the fall or spring. The offshoots must be kept moist and replanted immediately.
Iroquois, Meskwaki, and Cherokee Indian tribes used the great blue lobelia to cure medical and psycho-social issues. The Iroquois used the plant as a cough medicine. In the Meskwaki tribe, the roots were ground and secretly put into a dish that both the husband and wife were sure to eat. This was thought to prevent divorce. The Cherokee used the roots to make an infusion to stop nosebleeds and pulverized the entire plant to make a poultice for headaches.