How Long Does It Take for Cosmos to Bloom After Sprouting?

One of the easiest summer flowers to grow, cosmos (Cosmos spp.) are colorful, heat-loving annuals that bloom all summer long. They can be started indoors or sown directly in the garden, but either way, it takes about seven weeks from sprouting to mature blooms. Cosmos are popular cut flowers that hold their color well when dried.

Christened by Spanish monks in Mexico, the name "cosmos" means harmony or order in the universe. Although there are over 20 species of cosmos, the two most popular are Cosmos bipinnatus, with red, pink, maroon and white flowers, and Cosmos sulphureous, which blooms in shades of yellow and orange. Cosmos are heat-loving annuals and when sown directly from seed, begin to bloom about seven weeks after germination, producing continuous color until the first frost. The flower heads are often described as cup-shaped with wide petals surrounding a yellow center. The leaves of cosmos are lacy and resemble ferns, and the stalks grow from 4 to 7 feet tall.

Heat-loving cosmos do not tolerate frost, so either wait until the soil temperature warms to 65 degrees or start seeds indoors four to six weeks before the last frost date for your area. When direct seeding, sprinkle the seeds over the seed bed, cover with 1/16 to 1/4 inch of soil and tamp lightly with a garden rake to encourage contact with the soil. Keep the soil moist but not too wet. The seeds should germinate in anywhere from 7 to 21 days, depending on the temperature of the soil. Seven weeks the first blooms should appear.

If they are planted in moderately fertile soil and kept a little on the dry side, cosmos will bloom all summer long. If there is too much nitrogen in the soil or the plants are over watered, you will get foliage with few blooms. Removing the dead flowers throughout the season encourages longer blooming time. Frost kills cosmos, but if you leave a few flowers on the stalks, they often reseed themselves the following year. The colorful blooms of cosmos are often planted in cottage and cutting gardens for use in flower arrangements, but they are also attractive to bees, butterflies and hummingbirds.

Save some of the summer color by drying the flowers of cosmos. They dry well and keep their color for years. Hang bunches of flowers upside down or use a desiccating agent such as silica gel, borax powder, sand or kitty litter. The dried flowers can be used in bouquets, arrangements or wreaths.