The cardinal flower (Lobelia cardinalis) is a water-loving plant that grows bright-red, spike-like flowers during late spring and early summer. Lobelia cardinalis has purplish foliage and attracts swallowtail butterflies as well as hummingbirds. Native to parts of Canada and the United States, the cardinal plant can grow 2 to 4 feet tall and 1 ½ to 2 feet wide at maturity. The cardinal flower grows best in non-tropical regions, in USDA Hardiness Zones 4 through 8, where minimum winter temperatures stay above minus 30 degrees F.
Plant your cardinal flower in full to partial sunlight and in moist soil supplemented with organic compost or aged manure.
Spread a 1-inch layer of organic material such as compost, manure or leaf mold (humus) on the ground around the base of the cardinal plant. Spread a fresh layer of organic material each year in the spring.
Spread a 2-inch layer of bark mulch around the base of the cardinal flowers to retain soil moisture levels.
Water your cardinal plants two or three times each week during the growing season to supplement rainfall. Water the flowers deeply to soak the soil down to the roots.