Sulphur Cosmos Information – How To Grow A Mexican Aster Flower

Orange Sulphur Cosmos Flowers
(Image credit: Biscut)

With a little basic Sulphur cosmos information (Mexican aster) you can easily grow this lovely, sunny annual in your flower garden. It’s easy to grow even in poor soil. Mexican aster makes a great addition to beds and meadows. They are pretty and cheerful but also attract useful pollinators, like butterflies and bees. 

What is a Mexican Aster? 

The Mexican aster flower is also known as Sulphur cosmos. The story of this latter name is that Spanish priests grew the flower in their missionary gardens in South and Central America. Native to this region they appreciated the perfect placement of the petals on the flowers. They named them the Greek word cosmos, which refers to an ordered universe or universal harmony. 

Sulphur cosmos belongs to the Asteraceae family of plants. It produces red, orange, and yellow daisy like flowers on top of stalks that grow up to six feet (almost 2 meters) tall but are more commonly only three or four feet (about 1 meter). 

The cheerful, sunny flowers bloom in profusion from summer to fall. They look best in a meadow or naturalistic flower bed and provide a large splash or cluster of warmer colors in any bed. You’ll find a few different varieties of Mexican aster, including some dwarf types and those that produce double blooms. 

Growing Sulphur Cosmos

Sulphur cosmos plants grow readily in full sun. They tolerate drought and poor soil, so they are pretty easy to grow in nearly any garden as long as you have sun. You can start from seed, either sowing indoors or in beds to a depth of one-sixteenth of an inch (0.2 cm.) or by scattering in a bed and raking into the soil. If starting outside, the soil should be 70-80 F. (21-27 C.). 

You shouldn’t need to water this plant very often, as they tolerate dry soil well. As the flowers come and go, deadhead the plants regularly. This will encourage bushier growth and continued blooms. Since the stems can grow quite tall you may need to stake them. 

This is an annual plant but does readily self-sow by seed. If you leave some flowers in place they will reseed. To better control the growth and spread of your Sulphur cosmos, though, you can collect seeds from the spent flowers and use them next year.

Mary Ellen Ellis

Mary Ellen Ellis has been gardening for over 20 years. With degrees in Chemistry and Biology, Mary Ellen's specialties are flowers, native plants, and herbs.