Cosmos bipinnatus is a half-hardy annual that flowers June to October in UK gardens. Sow indoors from March to April at 18-20C, or direct sow outdoors in May after the last frost. Plants grow 60cm to 1.5m tall depending on variety. Full sun and poor soil produce the best flowers — feeding causes leafy growth instead. Cosmos self-seeds readily and attracts hoverflies and bees.
Key takeaways
- Sow indoors from March to April at 18-20C, or direct sow outside in May after the last frost
- Poor soil produces more flowers — avoid feeding with nitrogen-rich fertiliser
- Deadhead every week from June onwards to extend flowering until October
- Sensation Mix and Double Click are the most reliable UK varieties for cut flowers
- Chocolate cosmos (Cosmos atrosanguineus) is a tender perennial — lift tubers in autumn to overwinter
- Cosmos self-seeds freely — leave a few spent heads to get free plants next year
cosmos annual flowers seed sowing cutting garden wildlife gardening
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
