Updated: Jan 19, 2022
Lobelia (Lobelia erinus) is an attractive annual plant that blooms profusely from early summer to the first frost in autumn. The plant is available in compact, bushy forms or trailing varieties. Although it’s possible to propagate lobelia from seed, many gardeners prefer instant color provided by young, nursery-grown plants. Lobelia is perennial in U.S. Department of Agriculture plant hardiness zones 10 and 11.
Lobelia is a small plant that generally grows to heights no taller than 10 inches. Bush types spread only five to nine inches, but trailing varieties expand as much as 1 1/2 feet. Although electric blue lobelia is the most common hue, the plant is available in a variety of colors including white, pastels of lavender or pink and vibrant purples and reds. The blooms sometimes take a break during the hottest part of summer, returning to full bloom when temperatures drop in autumn.
Lobelia is available in a number of cultivars, including “Blue Moon,” which displays dark blue flowers, and “Crystal Palace,” a familiar variety with deep blue blooms and greenish-bronze foliage. “Rosamunde” is one of the few varieties that displays bright red blooms, while “Paper Moon” is stunning with pure white flowers. “Sapphire” is a trailing, purple variety, and “Waterfall” is an unusually tall variety at 12 inches, in colors of white, lavender and blue.
Lobelia is a good choice for a rock garden or butterfly garden, as several butterfly species are attracted to the sweet nectar and bright colors. Hummingbirds love lobelia in shades of red or bright purple. Lobelia is stunning along a border, as a mass planting in a flower bed, or cascading over the sides of a patio container or window box.
Lobelia thrives in full sun but benefits from afternoon shade in hot climates. Any type of well-drained soil is suitable, including sandy, clay, or acidic soil. Although the plant blooms best in cool weather, it also performs well in climates with sunny, cool summers. Lobelia is rarely bothered by pests and disease, but too much moisture may result in root rot or stem rot. Water at the base of the plant to keep the foliage dry, and allow the soil to dry slightly between waterings. Lobelia benefits from application of a general-purpose garden fertilizer every other week throughout the blooming season.