Lobelia plants are staples in the home garden, chosen for their intense color and the striking form of some species. The genus Lobelia includes several hundred species that are part of the campanula (Campanulaceae) family. Most types of lobelia have the bell-shaped blossoms characteristic of the campanulas, but otherwise they may differ dramatically in appearance.
Edging and Trailing Varieties
Lobelia erinus is a perennial in USDA plant hardiness zones 10 to 11, usually grown as an annual in cooler zones. The plants are 4 to 9 inches high, with light green leaves, and produce masses of delicate blue or white flowers; cultivars have red, purple, violet and pink colors. Compact, upright forms are used for border edging and rock gardens, while trailing varieties suit plant containers, window boxes and hanging baskets, where they can spill over the edge.
Cardinal flower (Lobelia cardinalis) is native to North America in USDA zones 3 to 9, growing 2 to 3 feet high with an upright mound of green foliage, and bearing short-lived, scarlet-red, tubular flowers on spikes. Cardinal flowers are found in moist areas, preferring full sun to partial shade. Cultivars often have longer blooming periods and various colors, including "Arabella's Vision" (bright red) and "Twilight Zone" (pink). Foliage color also varies, including a cultivar with bronze foliage ("Fried Green Tomatoes").
Mexican Lobelia and Great Blue Cardinals
Mexican lobelia (Lobelia fulgens) grows wild in Mexico and Texas, or USDA zones 7 to 9. It's similar in appearance to L. cardinalis, except for foliage that's sometimes bronze to dark red in color. Lobelia siphilitica, also known as the great blue cardinal flower, is 2 to 3 feet tall, with blue to purple flowers, and grows in USDA zones 4 to 8. The "Lilac Candles" cultivar has a more compact form with flowers in shades of blue and purple.
Hybrids developed from Lobelia fulgens, L. cardinalis, and L. siphilitica are designated as Lobelia x speciosa. Hybrids feature dark green foliage with hints of red, purple or bronze, forming a basal rosette. Tubular flowers grow on spikes in lavender, pink and red colors, with long blooming periods from July to September. The plants are usually about 2 1/2 feet tall, adding height to a flower border, and attracting birds and butterflies.
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