LSU AgCenter Horticulturist
Are you looking for a gorgeous flower that thrives on pure neglect? Try cosmos. They are one of the most beautiful and easiest flowers to grow. While you’ll have to wait until the spring to plant seeds, look around this fall, and you may notice these flowers blooming profusely in local gardens.
Cosmos are a true heirloom flower that will grace just about any garden — regardless of soil type — with colorful blooms. Multi-branched stems hold several flower heads, each on long, individual stems. This makes them a great cut flower to bring indoors and use for beautiful bouquets.
Native to the southwestern United States and Mexico, Spanish explorers brought cosmos back to Spain in the 16th century where Spanish priests cultivated them in their mission gardens. The flowers were given the name “cosmos,” the Greek word for “ordered universe or harmony” because of their evenly spaced petals. Their appearance is similar to other members of the aster family with a daisy-like flower head.
Cosmos blooms begin in late summer and continue until first frost. They attract bees, butterflies and hummingbirds in addition to many other types of pollinators.
Cosmos do not need much to thrive. Growing from seeds is simple. Plant in the spring after the danger of frost has passed.
You can rake the garden soil and scratch the area to make germination more successful. Cover seeds lightly with 1/8 to 1/4 inch of soil. Plants will pop up in seven to 14 days, and blooms will begin in approximately seven weeks or in late summer, lasting throughout the fall.
When germinating, seeds will need water to get started, but once the plants have established, you can basically forget them. They are very drought tolerant.
Tall flowers can become top heavy and topple over without support. Planting cosmos en masse, or in large groups, can help the flowers support one another. For the most flower production, be sure to plant in full to partial sun in a well-drained soil. Plants are essentially pest-free and do not have any major disease issues.
One of the most common cosmos is tall garden cosmos (Cosmos bipnnatus), an herbaceous annual that reseeds itself and grows up to 4 feet with flowers of pink, purple, red and white. Some suggested varieties are Dazzler (pink), Gazebo Red (dwarf), Fizzy Pink, Picotee (dark purple), Purity (white), Rubenza (red), Sea Shells (pink, red and white) and Sonata (pink, red and white). The second most common type is the sulfur cosmos (Cosmos sulphureus), which can grow up to 7 feet with colors of orange, red and yellow and coarser foliage than those of the common garden cosmos. Look for Cosmic Yellow, Sunset Orange and a dwarf variety called Bright Lights.
Besides looking great in the garden, cosmos are a wonderful cut flower. It’s best to cut flowers in the early morning or late evening. Select those that have just opened with a tight center. You can use a pair of hand pruners or scissors. Place flowers in water immediately and remove any lower leaves that would sit under the water line to prevent decay.
You can keep flowers producing by deadheading or trimming plants back. Or you can let them go to seed to collect seeds for next year or share them with neighbors and friends. Saving cosmos seeds is a cinch!
When the flower head produces mature flower seeds, you can harvest the spiky seeds once they dry and turn brown. Carefully grab a handful of the seeds — they fall off easily — and store them in a cool, dry place. Paper envelopes and bags are the best to prevent moisture. Be sure to label the bag with the year and seed type. Harvested seeds may not be true to type, meaning they may not look like the parent plant.
Try cosmos if you are looking for a no-care plant that produces without a fuss. Seeds are available at local garden centers and online, or you can purchase transplants in late spring for a fantastic floral fall display next year.
We love cosmos so much here at the LSU AgCenter that it is featured on the cover of the 2022 Get It Growing Lawn and Garden Calendar. This calendar is filled with a year’s worth of gardening tips, plus inspiring photos that were selected in our annual statewide contest — including Nadine Melancon’s cover photo of a bee visiting a purple cosmos flower. There’s also a special feature on hydrangeas, a how-to section on creating a rain garden and lots of other useful information.
The Get It Growing calendar makes a great gift for that special gardener in your life — or for yourself! You can purchase a copy for $11.95 online at LSUAgCenter.com/OnlineStore or at your local garden center.
Pink and purple common garden cosmos are lovely heirloom flowers. Photo by Heather Kirk-Ballard/LSU AgCenter
Pollinators love cosmos. They attract bees, butterflies, hummingbirds and many other types of pollinators. Photo by Heather Kirk-Ballard/LSU AgCenter
Saving cosmos seeds is a cinch. Harvest seeds when they have dried out and turned brown. Photo by Heather Kirk-Ballard/LSU AgCenter
A field of cosmos and zinnias at the LSU AgCenter Botanic Gardens at Burden. Photo by Heather Kirk-Ballard/LSU AgCenter