NC State Extension

Cosmos Brings Beauty to Your Universe

Cosmos bipinnatusRobert E. Lyons ©

Cosmos bipinnatus
Robert E. Lyons ©

Cosmos is an easy-to-grow flower that can reseed itself and grow in hot, dry conditions, making it a good choice for North Carolina gardens. Homeowners can find the two most common species of cosmos by asking their local suppliers for Cosmos sulphureuswhich will have golden-yellow or orange flowers and Cosmos bipinnatus with a variety of maroon, pink, lavender and white flowers. Gardeners can take advantage of the naturally smaller growing Cosmos bipinnatus varieties such as ‘Gloria’ pink, ‘Versailles Tetra’ red, ‘Candy Stripe’ white with red veins, ‘Day Dream’ white with red halo around yellow stamens, ‘Picotee’ white petals with red margins, ‘Sea Shells’ and ‘Dwarf Sensation Mix’, both sold as mixed colors usually in pink pastels, and ‘Psycho White’. Both cultivars may grow up to 6 feet depending on soil conditions and may need staking if subjected to high winds and frequent storms.

Plant cosmos in a location that receives at least a half day of direct sunlight. Sow the seeds outdoors after danger of frost is past and when the soil has warmed to at least 65 degrees. Rake seeds into a loose soil; 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.

AAS Winner Cosmos 'Cosmic Orange'Robert E. Lyons ©

AAS Winner Cosmos ‘Cosmic Orange’
Robert E. Lyons ©

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.

Each year, the JC Raulston Arboretum evaluates at least one cultivar in its trials area for annual plants. The ‘Cosmic’ series is the latest entry into this arena and is both dwarf in stature and quick to go to seed. When you visit the trials, take a look at the adjacent Perennial Border for the original species of Cosmos sulphureustowering over most other plants with its cascading sprays of orange flowers.

David Barkley

Page Last Updated: 3 years ago
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