Lobelia is a flower that grows 3 to 4 feet tall and 1 to 2 feet wide. The dainty tubular blossoms are red, pink, blue and white. This summer flower thrives in USDA plant hardiness zones 3 to 9. Lobelia is a short-lived perennial with a life span of three years. It is commonly used as an annual and re-planted each year. Lobelia is used in garden borders, butterfly gardens, window boxes and hanging baskets.
Remove the grass, weeds, brush, debris and rocks from the planting site after the last spring frost date has passed. Locate the planting site in partial shade unless growing in a cooler climate; then the lobelia will need full sun exposure.
Turn the soil over with a shovel to loosen it. Remove any stray weeds and grass with a garden hoe. Break up dirt clods with a quick, short sideways motion of the hoe.
Work in a 3- to 6-inch layer of well-rotted manure. This creates a moist, good-draining soil enriched with organic material. Rake the soil smooth and level.
Dig a hole as deep as the lobelia root ball with a hand trowel. Remove the lobelia seedling from its container. Spread the roots out if the roots look like they are growing in circles. Place the lobelia in the hole at the same level that the flower was growing in its container.
Fill the hole with soil and gently firm the soil around the lobelia to hold it in place. Plant the rest of the seedlings 6 to 24 inches apart depending on the variety. Sprinkle the planting area with water until the soil is wet.