Posted by Aaron Barton on Apr 4th 2023
Lobelia (Cardinal Flower/Great Blue)
Charming gardeners and pollinators alike, Lobelia, of the Lobeliaceae family, are a colorful group of over 1,000 species toting gorgeous fan-shaped, tubular blooms beloved by wildlife, especially hummingbirds. Standout specimens in wetlands, pollinator gardens, rain gardens, stream and pond margins, open woodland gardens, and moist sunny borders, Lobelia are native to a range of tropical and temperate regions throughout the world, with key perennial species native to North America including right here in Minnesota.
Lobelia cardinalis (low-BEE-lee-ah kar-dih-NAL-iss), or cardinal flower, is a bright late season bloomer, forming lush upright clusters of lance-like, shiny green foliage on unbranched stems, maturing to 36-48” tall and 12-24” wide. Blooming from mid-summer into fall, Lobelia cardinalis produce large, densely blooming terminal racemes of stunning scarlet red flowers that bloom from the bottom up. Growing up to two inches long, each tubular flower is comprised of a split two-lobed upper lip and spreading fan-like, three-lobed lower lip of three equally sized petals, as well as a hook-like style that arches upward between the upper petals. Cardinal flower blooms are excellent nectar sources for butterflies and hummingbirds, especially the ruby-throated hummingbird, its primary pollinator. Tolerant of a range of conditions from sandy to heavy clay soils, cardinal flower is an easy-care perennial, so long as it does not dry out completely. Lobelia cardinalis thrive in full or part sun conditions in evenly moist or wet soils, tolerating brief flooding in up to three inches of standing water, and performing best in the landscape with a topdressing of compost and mulch to retain moisture in the root zone.
Lobelia siphilitica (low-BEE-lee-ah sigh-fy-LY-tih-kuh), or great blue Lobelia, is another excellent late season bloomer for wet sites, forming upright clusters 24-36” tall and 12-24” wide. Also blooming from mid-summer into fall, great blue Lobelia produces tall terminal racemes of beautiful soft blue blooms beloved by pollinators and hummingbirds for their excellent nectar supply. Unlike cardinal flower, however, great blue Lobelia are primarily pollinated by bumblebees, which use the flower’s lower lip as a landing pad, the weight of the bee in turn lowering the flower stigma against its back to transfer pollen as they make their way toward the nectar further inside the bloom. Slightly more compact than cardinal flower, great blue Lobelia bloom tubular flowers up to one inch long, with a curled, two-lobed upper lip and fused three-lobed lower lip. As opposed to the equal petals of the cardinal flower, the middle of the three lower petals of Lobelia siphilitica is typically larger, with two lighter-colored, almost fang-like raised bumps on either side, as well as a curved style that resides between the upper petals. Like cardinal flower, great blue Lobelia is tolerant of a wide range of conditions so long as it does not dry out completely, preferring full or part sun conditions in evenly moist or wet soils, though great blue Lobelia is slightly more tolerant of brief dry periods than its crimson-bloomed relative.
While perennial Lobelia species tend to be shorter-lived species, typically lasting three to five years in the garden, they are certainly worth the effort and will continue to appear in the garden if allowed and conditions are favorable. After setting seed, flowering stems and their roots will die; however, basal offsets will follow, though care should be taken to not bury these tender young plants when mulching for the winter season. Additionally, Lobelia reseed effectively to replenish populations if seeds can make good soil contact, needing light to germinate, but unwanted seedlings are easily removed. Rest assured that deer and rabbit will not interfere either, as Lobelia naturally produce lobeline, a toxic alkaloid compound that deters herbivory.