Cosmos bipinnatus

Introduced to the US as an ornamental flowering plant from Mexico or tropical America, tall Cosmos offers a variety of daisy-like maroon, pink, lavender, and white flowers on stalks that will get up to 4 feet tall. The word cosmos is derived from the Greek word for harmony, referring to its evenly placed petals.  Although many cultivars and varieties are available, two annual species, Cosmos sulphureus (Yellow Cosmos) and Cosmos bipinnate are the most familiar to the public.

Plant cosmos in a location that receives at least a half-day of direct sunlight. Sow the seeds outdoors after the danger of frost is past and when the soil has warmed to at least 65 degrees. Rake seeds into a loose soil as planting seeds too deeply will hinder germination. Keep the soil moist for 5 to 10 days after seeding. Seeds will germinate in 7 to 21 days. Cosmos needs only basic care to provide an abundance of colorful blooms all summer. Taller varieties may need staking if subjected to high winds and frequent storms.

When the spring-planted cosmos appears to have an abundance of dried seed, do not remove the plants. Encourage re-bloom by cutting the plants back to 12 to 18 inches high. They will be back in bloom in a month and the seed that is cut off will fall to the ground, germinate in the hot soil, and increase the density of your plant population and the eventual bloom display.

Although non-invasive, it will aggressively self seed.  Deadhead to prolong the flowering period.  

In addition to the basic color choices, many variations are available in the form of hybrids.  They are typically pastel.

Insects, Diseases, and Other Plant Problems:  Stem canker, powdery mildew, and gray mold are common issues.  Insects include aphids, Aster Leafhopper and the Gray Looper Moth.

They may require staking due to their height.  Protect from strong winds.  Overwatering or overfertilizing can lead to plants with fewer blooms.  

To prevent self seeding, remove the spent blooms before the seed spreads.