Blue Mistflower (Conoclinium coelestinium) has showy, flat-topped terminal clusters (corymbs) of purple-blue flowers from late summer into the fall. Individual fluffy, tubular flowers are about a half-inch in diameter. Flowers are a lavender blue color of disk flowers but have no ray flowers. Conoclinium spreads by self-sown seeds as well as by underground rhizomes. Mature height is up to 2 to 3 feet, with a similar diameter, but is generally smaller in Central Florida.
Leaves are opposite along the branching stems and have rounded deltoid to triangular-shaped leaves with toothed margins.
This native wildflower ranges from Southern Ontario, Michigan and New York south to Florida, and east to Texas and then as far north as Nebraska. This pretty, short-lived, herbaceous perennial grows naturally in 26 states, Washington, D.C. and Southern Ontario in United States Department of Agriculture (USDA) cold hardiness zones 5 to 10.
USDA cold zones are based on average minimum winter temperatures. Florida has four full 10-degree Fahrenheit zones, each divided into 5 degree a and b halves as follows: Zone 8a — 10 to 15 degrees; Zone 8b — 15 to 20 degrees; Zone 9a — 20 to 25 degrees; Zone 9b — 25 to 30 degrees; Zone 10a — 30 to 35 degrees; Zone 10b — 35 to 40 degrees; and, in the Florida Keys, Zone 11a — 40 to 45 degrees.
Modern accurate, instantaneous, science-based records mean the cold zones can be updated as needed rather than on a hundred-year average as in the past. As a consequence of warmer winters and climate change, there is no longer a Cold Zone 7b — .05 to 10 degrees, in the highlands of the West Florida Panhandle. In the coming winter, in zones 9a and 9b in Central Florida still will have frosty mornings and a couple of hard freezes. Because winters are warmer, homeowners can now grow semi-tropical native and exotic plants in protected areas in their landscapes.
Conoclinium dies to the ground in winter but regrows from underground rhizomes in spring. Seeds generally lie dormant overwinter and germinate in spring.
A member of the Aster family (Asteraceae), Conoclinium can grow throughout peninsular Florida in moist but well-drained, humus-rich soils. Cut off dead flower stalks in winter when the plant is dormant, but do not pull up the rhizomes or roots. Seed and seedheads may be gathered in fall, allowed to dry naturally and can be stored in paper bags or envelopes in an unheated, dry place. In spring, sow the seeds directly on bare ground after the danger of frost is past. Be aware that April and May are dry months in Florida. That means seedlings may need regular irrigation until natural rains begin in June in Florida.
Old timer gardeners incorrectly considered Blue Mistflower to be akin to the annual, non-native bedding plant species ageratum (Ageratum conyzoides), in the Family Eupatorium. But modern science verified it is a Conoclinium. Mistflower is an excellent nectar source for skippers and other butterflies. Bees gather its pollen. Small songbirds eat the seeds and help spread seeds to nearby natural areas.
This pretty blue wildflower looks great near water features and can spread to form a large clump. Mature clumps can be dug and divided in early spring. Conoclinium can tolerate full sun further north but grows better in part or afternoon shade in hot, humid, subtropical Florida summers. It is not salt-tolerant on the coasts but adapts to both alkaline and acidic soils. I recommend amending dry sandy soil with ample decaying organic vegetable such as the finely milled mulch available free from Central Landfill on State Road 44 between Lecanto and Inverness. The organic material holds soil moisture and decays to provide nutrients to plants.
To see the range map for Conoclinium, visit https://tinyurl.com/y35b92ta.
Jane Weber is a professional gardener and consultant. Semi-retired, she grows thousands of native plants. Contact her at email@example.com or phone 352-249-6899.