Over 300 lobelia species are found over a range of 10 hardiness zones. Some cultivars survive in temperatures over 32.2 degrees Celsius, while others survive temperatures as low as 7.22 degrees C below zero. Perennial varieties will survive through winter.
Cardinal flower, Lobelia cardinalis, is indigenous to the United States, from Maine to Florida and both coasts. Healthy plants overwinter successfully in well-composted soils. Cardinal flowers used as marginal pond plants may have to be transplanted to a temporary winter location if there is a chance they may fall into the water or shed leaves into the pool.
Great Blue Lobelia
When left in the ground great blue lobelias successfully overwinter without much care. Every effort should be made to insulate containerised plants. The plant will not survive if its roots freeze. Place containers on mats and keep containerised plants in warm, sunny locations.
This low-growing, small-flowered cultivar is found in borders, planters and hanging baskets. Flower colours range from white, to blue to violet. Unlike the cardinal flower and great blue lobelia, Loblelia erinus, is an annual plant that thrives in hot weather. Once the warm season ends the flower and plant die.
- The United States National Arboretum: Hardiness Zones Details
- Fine Gardening: Genus Lobelia
- United States Department of Agriculture: Cardinal Flower Plant Guide
- United States Department of Agriculture: Great Blue Lobelia Plant Guide
- The Lady Bird Johnson Wildflower Center: Ask Mr. Smarty Plants
- North Carolina State University: Lobelia Fact Sheet