The great blue lobelia (Lobelia siphilitica} is a short-lived perennial that is native to eastern and central North America, including Canada and the United States. It is also called the Blue Cardinal flower and is related to the Red Cardinal Flower (L. cardinalis), another North American native plant.

Native Americans had many medicinal uses for this plant. They used it to treat respiratory ailments as well as like aspirin to treat muscle aches. They made a strong tea with the mashed plant to treat venereal disease and gargled with it to treat coughs. The tea was also used to fight bewitchment and to end quarrels among couples and renew their love.

Care should be taken when ingesting this plant. It contains toxic alkaloids which can induce nausea, vomiting, diarrhea, excessive salivation, weakness, exhaustion, dilation of the pupils, convulsions, coma, and even death. All parts of the plants contain these alkaloids.

The flowers can also be white

The great blue lobelia is hardy in zones 4 – 9. It grows 3 to 4 feet tall and 1 to 1 ½ feet wide. The leaves are attached directly to the stem, lancelike and 2 to 6 inches long and 2 inches wide. The flowers are bright blue but can also occasionally be white. They have five petals The three lower petals are fused. They are usually pollinated by bumblebees which are large enough and strong enough to force the petals apart and enter the flowers. Bloom time is August through October. Great blue lobelia will self-seed but not so prolifically that they become a nuisance.

The great blue lobelia prefers partial shade but will grow in full sun. It likes moist to wet soils. It is often found swampy forests, roadside ditches, floodplains, and the banks of lakes. Keep it well-watered in your garden or grow it in that low area of your yard that always seems to be wet.

The plants have a large central taproot which often grows offsets in the form of small rosettes around the base of the plants. You can use these to divide your plants. Use a garden fork to carefully dig up your plants and a sharp knife to cut off each small rosette, making sure that each rosette has both roots and foliage. Plant the divisions 8 to 12 inches apart. It is recommended that you divide your plants in the spring.

Like many native plants, the great blue lobelia is easy to grow from seed. The easiest way to do it is to allow your plants to go to seed in the fall, dropping their seeds directly into your garden where they will germinate in the spring.

You can direct sow seeds in the spring after your last frost. Surface sow them. Do not cover them with soil. They need light to germinate. Germination should occur in 14 to 30 days.

You can also start seeds indoors, 8 weeks before your last frost. Surface sow them. Do not cover them with soil. They need light to germinate. Germination should occur in 14 to 30 days. You can transplant your seedlings into your garden after your last frost, spacing them 8 to 12 inches apart. Unlike most perennials, the great blue lobelia will flower the first year.