Louisiana Master Gardener volunteers maintain the beds in front of the LSU AgCenter office in Amite. They’ve been beautiful lately, with orange, pink, red, and blue flowers, in addition to the purple flowers of the ‘Shoal Creek’ chaste trees in front of them. One flower that’s present in abundance is yellow cosmos, which reseeded itself from last year’s plants.
I generally favor perennials, because I like plants that provide multiple years of returns on my planting investment. However, the beauty provided by annual flowers like cosmos is undeniable. Furthermore, cosmos, like their zinnia relatives, often reseed themselves. They also support pollinators such as bees and butterflies and can be used as cut flowers, though their vase life is somewhat short.
Cosmos are in the aster family with sunflowers, black-eyed susans, zinnias, and many other beloved flowers. Two kinds are commonly grown.
Yellow cosmos (Cosmos sulphureus) flowers tend, as one might expect, to be yellow or orange, while those of garden cosmos or Mexican aster (C. bipinnatus) are often pink, red, or white. However, there is some crossover in flower colors, and the shapes of the leaves are probably a more reliable way to distinguish between the two species. Yellow cosmos leaves remind me of ragweed. Garden cosmos foliage has a more delicate, lacy appearance.
Both species are native to Mexico, with the native range of yellow cosmos extending into Central America.
Cosmos can be seeded or transplanted in spring, after the last frost. If sowing seeds, wait until soil temperatures have reached about 65 degrees F or greater. Plant on a well-drained site with full to partial sun exposure.
Let me know if you have questions.
Dr. Mary Helen Ferguson is an Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at mhferguson@agcenter.lsu.edu or 985-277-1850 (Hammond) or 985-839-7855 (Franklinton).
