How To Grow Cosmos Seeds
Updated on Nov 18, 2021
By Shannon McCabe
Latin name Cosmos bipinnatus is an herbaceous perennial member of the Asteraceae, or daisy, family. Plants grow as annuals in areas with frost, but will readily reseed in place the following spring. They grow easily from seed and tolerate a wide range of soil conditions, even poor soil. Cosmos are quite drought and heat tolerant but do not handle frost. These carefree flowers are a staple for landscaping and cut flower production.
HISTORY
Native to Mexico, the plants were brought back to Spain and quickly adopted across Europe. They were especially beloved in Spanish monastery gardens.
USES
- Ornamental, pollinator gardens, beds, borders, butterfly garden, containers, wildflower meadows.
- Visited by a number of pollinators including bees and butterflies.
- Seeds germinate in 7-14 days.
- Sow the long, slender seeds horizontally and cover lightly with a thin layer of soil.
- Direct sow outdoors after all chance of frost has passed and soil has reliably warmed to 60 F, or start indoors 3-4 weeks before last frost date has passed.
- Ideal germination temperature is 70-75 F.
- Plants prefer full sun and poor or moderate soil (excessively rich soil leads to losts of foliage and few blooms).
- Space plants 14-24 inches apart; the more space, the stronger the plant!
- Staking is not essential but can benefit plants, helping to prevent the central stem from splitting from the weight of blooms.
- Keep plants deadheaded.
PESTS/SPECIAL CONSIDERATIONS
- Generally pest and disease-free, cosmos prefer hot, dryish conditions; excessive moisture and humidity or cool temperatures can cause issues.
- Cosmos can sometimes be plagued by fungal pathogens like fusarium and powdery mildew. Adequate spacing and drip irrigation (to keep foliage dry and humidity around plants lower) is the best way to prevent these diseases.
- Bacterial wilt can also affect cosmos; there is no cure for bacterial wilt, so the best prevention is to provide plants the conditions that they thrive in—hot and dry, with good air circulation.
- Cosmos are insect-pollinated, and there may be some crossing between varieties in the garden. You can enjoy the mixing or use caging techniques and hand pollination to avoid crossing.
- Saving seed from cosmos is easy: simply allow the heads to brown and dry on plants and collect seeds. Store in a cool, dry, dark place over winter.
