When to plant cosmos seeds outdoors

Updated February 21, 2017

If you are starting a garden with a small child, there isn't a plant that is easier to plant than cosmos. This adaptable flower can tolerate any soil condition and sprouts easily when planted in the soil. Before long, a continuous bloom of colour erupts from the ground. The display lasts from early spring until the first frost of fall.


Cosmos is actually a species of more than 20 annual and perennial plants that are native to Mexico. There they grow in scrubby and meadow areas. Cosmos are related to aster, daisy and sunflowers. According to the Texas A&M horticulture website, Spanish priests to Mexico first adapted the cosmos to grow in their gardens. Because the flower had evenly placed petals, the priests named it cosmos, which is the Greek word for harmony and ordered universe.


Because of the showy display of flowers as well as the ease in which cosmos germinates and the tolerance that the plant shows for poor soil, cosmos is a popular choice for growing from seed. Cosmos can be planted outdoors anytime after the danger of frost has past, once soil temperatures reach 18.3 degrees Celsius. Cosmos will usually bloom within 14 days of germination. It requires full sun and needs eight to 10 hours of sunlight. In warmer climates, cosmos can be sowed into the ground in September, and will bloom all winter long. To plant cosmos, turn the soil over to break up the sod and work the soil into an even consistency with a garden claw. Create a ridge in the soil, and plant the seeds 1/2 inch apart. Lightly cover the seeds with soil and water. Continue to water daily until the plants germinate. The plants will require adequate drainage, and are very drought tolerant. This makes them a popular choice for southwestern gardeners.


Plants can reach between 4 and 7 feet tall. In rich soil, the plants grow incredibly tall and lanky. Do not fertilise cosmos. The plant is not a heavy feeder and fertilising will cause cosmos to produce more leaves and fewer flowers. Typically, if cosmos does not thrive, it is because it has been overwatered or over-fertilised. The plants can be cut back when seed pods form to encourage a new spurt of blooming. The seed pods that are cut back generally germinate and produce thicker clumps of cosmos.

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About the Author

Tracy Morris has been a freelance writer since 2000. She has published novels and numerous online articles. Her work has appeared in national magazines and newspapers including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World." She holds a Bachelor of Arts in journalism from the University of Arkansas.