The common name of cardinal flower, whether referring to a bird’s plumage or a religious’ robes, is an indicator of the flower’s color. However, neither can match the true spectacle and brilliance of this species of lobelia in bloom. Since the flower is a hummingbird favorite, you can add plumage of the ruby-throat to the show when they come to feed during August and September while cardinal flower is in bloom.
Lobelia cardinalis can reach two to four feet in height depending upon growing conditions. The stems are hairy with alternate leaves which are oblong in shape. Leaves and stems will often have red coloration overlaying the green. Stems are usually unbranched and upright, yet resist being blown over in wind and rain while in bloom.
Blooms are in spike-like racemes at the top of the stems for perfect display. Each flower has a brilliant red corolla about 1 ½ inches long in a raceme that may reach a foot in height. The upper lip has 2 lobes, the lower 3, with extended stamens and stigma in the center and nectar in a pool at the back of the tube. When a hummingbird reaches for nectar the back of his head brushes the stamens and stigma thereby pollinating the flower.
Cardinal flower is native to the US east of the Rocky mountains from Canada to the Gulf states. In the wild its habitat will normally be places of extra moisture such as stream banks, ditches and ponds. With ample moisture they will grow in full sun, but seem to prefer a touch of afternoon shade to protect them from the hottest part of the day. Soil pH does not seem to be important to this species of lobelia. When grown in the garden soil rich in organics will make up for not having a pond or steam.
Lobelia increases from both seed and from offsets. Be careful when mulching this plant as seeds needs to have light to germinate, doing best on the surface of the soil. The tiny off sets forming from the parent plant will form rosettes the first year, producing blooms the second year. If mulched too heavily they can be smothered. I do not mulch lobelia in my garden and have seedlings as well as offsets forming colonies along with random seedlings about the garden. Watch for crowding out by other more aggressive plants as cardinal flower does not take competition well.
There are named cultivars of this popular native blooming in white and pink as well as a cross with our native great blue lobelia (L. siphilitica).
I have my cardinal flower companioned with Delphinium exaltatum, and ‘black’ foliage Actaea (Cimicifuga), along with the great blue lobelia. The larger ferns that love water such as the Royal and Ostrich would make great companions along with the foliage of Rodger's flower (Rodgersia).