Homegrown Habitat, August 2025: Great Lobelia
As August wanes, Sarah Middeleer focuses on a beautiful late-summer flower, great lobelia. Enjoy this quick video, too, which Sarah took in her yard. You can write to her at homegrown@ctaudubon.org.
Years ago, while visiting the English garden Hidcote with a group of fellow landscape designers, one of my companions overheard a young child say to his mother–in full aristocratic lilt–“Now there’s a proper lobelia!” I can’t tell you which species of lobelia this young garden enthusiast was admiring, but his exclamation sprang to mind while I was considering this month’s subject, Lobelia siphilitica, or great blue lobelia.
This slender-stalked, clump-forming plant is native to much of the eastern United States, the Midwest, Ontario, and Manitoba. Despite being hardy from zones four to nine, it is rare in northern New England–even extirpated from Maine–but is found in Connecticut. It usually grows in moist or wet conditions such as streambanks, swamps, and wet meadows, in either sun or shade. Blue lobelia also grows in a wide range of soil types, from sandy to clayey. In the garden it will tolerate soils with medium moisture content but then may need supplemental watering in dry spells, particularly in full sun.
Blue lobelia grows from one foot to five feet high (more often three or four feet), with a spread of 12 to 18 inches. Its stiff, erect stalks, emerging from basal leaves, produce deep blue, tubular flowers beginning in August and continuing into October, the bloom sequence proceeding from lower on the stalk upward. The flowers attract long-tongued bees, including bumblebees, as well as hummingbirds. It is quite entertaining to see a bumblebee go “bottoms up” into a great blue lobelia blossom.
Butterflies and hummingbird moths also visit great blue lobelia flowers, and the foliage is host to several species of moth larvae. Great blue lobelia has been named one of the 20 key pollinator plants blooming in August and September for the 2025 Great Southeast Pollinator Census.
A related species, Lobelia cardinalis, or cardinal flower, is very similar in growth habit to great blue lobelia but bears scarlet flowers and has a broader native range. Both species tend to be short-lived but will self seed easily. Thus you may not see a Lobelia exactly where you planted it originally, but may instead notice several popping up nearby. To encourage self sowing, gently rake at the base of the plant in fall to work fallen seeds into the soil.
The many garden settings suitable for great blue lobelia include perennial borders; pollinator, rain, and woodland gardens; and areas near streams, ponds, or water features. Recommended companion plants include swamp milkweed, Canada anemone, hardy ageratum (blue mistflower), and cinnamon fern. Wreath goldenrod and wood asters are other good companions for shady areas.
Lobelia has a long history of medicinal applications. The Latin name of great blue lobelia comes from its use to treat syphilis by Canadian tribes, which was described in Medicina Britanica by botanist John Bartram in the 1700s. Later this treatment was found to be ineffective.
The powerful alkaloids in great blue lobelia have also been used to treat asthma and other respiratory ailments but sometimes with lethal results. The Cherokee people infused the roots of both great blue lobelia and cardinal flower to treat nosebleed, and a poultice of the crushed leaves was used to treat headaches. Lobelia also produces a chemical called lobeline, which deters deer and rabbits.
Evidently great blue lobelia has even been used to remedy marital problems. The Meskwaki people are said to have mashed the roots and then surreptitiously put them into food to be shared by the troubled couple.
And yet, modern literature states that both species of lobelia are toxic to humans and pets.
Do you grow great blue lobelia? Drop us a line with comments or questions to homegrown@ctaudubon.org.
Resources
Websites
Great Blue Lobelia, Lobelia siphilitica – Virginia Native Plant Society
Lobelia siphilitica Great Blue Lobelia | Prairie Moon Nursery
Lobelia siphilitica (Great Blue Lobelia)
Lobelia siphilitica (Great Blue Lobelia)
Lobelia siphilitica | New Moon Nursery
https://bcnativeplants.net/plant-care-sheets/Lobelia-siphilitica-guide.pdf
