Botanical Name
Cosmos bipinnatus, Cosmos sulphureus
Common Names
Cosmos, Mexican Aster
Plant Type
Annual (though some varieties may self-seed)
Height
Varies greatly by variety, from 1 to 6 feet (30 cm to 1.8 meters)
Spread
Typically 1 to 2 feet (30 to 60 cm)
Flower Colors
White, pink, purple, red, orange, yellow, and bi-colors
Bloom Time
Summer to frost (deadheading encourages continuous blooming)
Foliage
Finely divided, feathery, light green leaves
Light
Full sun (at least 6-8 hours of direct sunlight daily)
Soil:
Well-drained, moderately fertile soil. Cosmos are surprisingly tolerant of poor soil and can even thrive in it. Avoid overly rich soil, which can lead to excessive foliage and fewer flowers.
Watering:
Water regularly, especially during dry periods and when plants are young. Once established, they are somewhat drought-tolerant. Avoid overwatering, which can lead to root rot. Water at the base of the plant.
Hardiness Zones
Typically grown as annuals in all zones.
Getting Started: Planting Cosmos
Transplanting: Gently remove seedlings from their pots and plant them at the same depth they were growing in their containers. Space them according to the mature size of the variety. Water thoroughly after planting.
Caring for Your Cosmos:
Deadheading: Regularly remove faded or spent flowers to encourage continuous blooming throughout the season. This prevents the plant from putting energy into seed production.
Fertilizing: Cosmos generally don't need much fertilizer. In fact, too much fertilizer can result in lush foliage but fewer flowers. If your soil is very poor, a light application of a balanced, low-nitrogen fertilizer once or twice during the growing season may be beneficial.
Support: Taller varieties may benefit from staking or other support to prevent them from flopping over, especially in windy conditions.
Pests and Diseases: Cosmos are generally relatively pest and disease-free. However, keep an eye out for aphids, spider mites, and powdery mildew, especially in humid conditions. Address any issues promptly with appropriate organic pest control methods or fungicides if necessary.