Plant type: Herbaceous perennial
Hardiness: USDA Zones 3 to 9
Appropriately named for its cardinal red flower spikes. Other species offer additional bloom color choices, including white, pink, lavender, purple and blue. Blooms from early to late summer. Leaves are narrow, dark green and four to six inches long. Cardinal flower is an excellent choice for consistently wet soils and is commonly found along streams, wetlands and low-lying woodland areas. Native to the eastern U.S. and Canada. Plant size ranges from two to four feet tall and one to two feet wide. Clump-forming.
How to use it: In masses, as a specimen plant and in containers. Use in a mixed perennial border, bog garden or naturalized in a woodland shade garden. Place next to a pond or water garden. Plant near a window to attract ruby-throated hummingbirds so you can see them up close.
Culture: Prefers a rich, moist to wet site; tolerates soggy soils. Use a light mulch, but be careful not to mulch too heavily so as to cause root rot, especially in the South. Plant in full sun (in northern, cooler climates) or (ideal) part shade. Deadhead flowers to promote branching and rebloom. Propagated through seed or division. This plant tends to be short-lived, but it self seeds, allowing it to continue on in the garden. Divide clumps about every three years in spring. No serious pest or disease problems.
Special notes: Member of the Campanulaceae family, or the bellflower family. There are over 200 species in the genus Lobelia. However, not all of them are ornamentally useful in the garden. Attracts wildlife, including birds (hummingbirds but not cardinals) and butterflies. Lobelia cardinalis is often eaten by deer. However, an alternative species, L. erinus, is deer resistant.
Selected cultivars and species
Great blue lobelia (L. siphilitica). Native plant that has striking blue flowers. Blooms later in the season than L. cardinalis. Grows two to three feet tall and one to two feet wide. Also prefers full sun to part shade and consistently moist site. Has herbal properties. USDA Zones 4 to 8. Lobelia x speciosa. Hybrid lobelia that offers alternative bloom colors, including purple, and dark purple foliage. Long-lived plant if planted in full sun (with preferably afternoon shade) and a moist site. Reaches three to five feet tall and one foot wide. Notable cultivars: 'Queen Victoria' has scarlet red flowers that contrast with bronzy foliage. Reaches four to five feet tall. 'Alba' is a white-flowering form that reaches two to three feet tall. 'Bee's Flame' has striking red flowers combined with purple-red foliage. 'Compliment Scarlet' offers large red flowers with green foliage, while 'Compliment Purple' has purple flowers. Zones 5 to 8. Edging lobelia (L. erinus). Has a spreading habit, only reaching four to eight inches tall and 18 inches wide. Great for edging, along a border, in hanging baskets or in a rock garden. Bloom colors are red, white or blue, and plants flower from spring to frost. In hot climates it should be grown in part shade. Tolerates full sun in cooler climates. Annual. 
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