Growing Cosmos Flowers


The Mexican aster, or Cosmos bipinnatus, has a solid reputation for being an easy seed for beginning gardeners to grow. Tall, lacy foliage with straight, fringe-edged petals create a carefree late summer and early fall annual display of color and height.

Step 1

Choose a full sun location with well drained soil, preferably without an abundance of clay. Seeds need moisture, but do not soak the ground or seeds once planted.

Step 2

Sow seeds outdoors when frost danger has past. Early spring temperatures between 68 and 86 degrees F will produce germination in anywhere from 7 to 21 days depending on the variety. Seedlings may crowd each other and still thrive with carefree, sprawling growth over the late summer and early fall.

Step 3

Provide shelter from wind and stake cosmos as they grow, to prevent delicate stems from bending or breaking. Varieties can grow up to 3 feet tall or taller.

Step 4

Remove spent blooms to support new growth. Do not fertilize, as cosmos will become spindly and produce fewer blooms if the soil is over-amended.

Step 5

Cut back dead foliage in the fall and compost. Cosmos seeds are not winter hardy and will need to be re-seeded in the spring for next season blooms.

Things You'll Need

  • Cosmos seeds
  • Garden stakes and twine


  • Wildseed Farms, Lady Bird Dwarf Lemon Cosmos
  • Michigan State University Extension, Cosmos bipinnatus--Mexican Aster
Keywords: cosmos care, care of cosmos, growing cosmos flowers

About this Author

Desirae Roy began writing in 2009. After earning certification as an interpreter for the deaf, Roy earned a Bachelor of Arts in elementary education from Eastern Washington University. Part of her general studies included a botany course leading to a passion for the natural world.