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.
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.
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.
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.
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.
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.