Lobelia erinus, commonly known as edging lobelia, hails from South Africa and has a history as a bedding plant in the United States as far back as the mid 1800s. Popular in modern-day gardens for containers, hanging baskets, and bed boarders, lobelia is not fussy and provides mounds of color in moderate seasonal temperatures.
If planting in a container or hanging basket, plan to move the receptacle if the summer sun becomes to hot. Rich, well drained soil that has been mixed with a time release fertilizer will create the best blend for success with lobelia. Follow manufacturer instructions for proper proportions of fertilizer for the size of container or basket you choose.
Choose a sunny bed location for lobelia, bearing in mind that very hot, direct sun can damage this delicate annual. Ensure good drainage and fertilize with your other bedding annuals. Allow one foot between plants for good air circulation and healthy growth.
To plant lobelia seeds, start them indoors for best results. Thompson and Morgan Seedsmen suggest you sow seeds, which are tiny and fine, 10 to 12 weeks before the last frost date in your area. Scatter seed over the surface of sowing soil. Close in a plastic bag until germination, 14 to 21 weeks later. Transplant seedlings into 3 inch pots, and continue growing in a cool, bright area indoors with brief visits outside to acclimate to the cool spring weather. Transplant after frost danger is past, allowing a foot between each plant in a bed.
Maintenance for lobelia is simple if you stay alert against hot, direct sun and regularly dead head old blooms. Simply pinch off the spent bloom to allow energy to flow to new growth. When the temperatures begin to heat up and blooms lessen, cut back the entire plant and wait out the heat. When temperatures drop and the fall season kicks in, lobelia should make a come back with a new crop of beautiful blooms.