Cosmos Seeds,
Japanese Kiiro

Plant cosmos only after the last frost when temperatures remain consistently warm. Seeds germinate best at temperatures between 70-75 F. Since cosmos are not frost-hardy, it is very important to check local last frost dates before sowing outdoors. The growing season lasts from spring to early fall, with blooms appearing from midsummer until the first frost. If you're uncertain about your frost-free dates, check out our blog post, 'Our Experts Answer Questions, Share Resources.'

Seeds can be sown directly into the garden after the last frost or started indoors 3-4 weeks before transplanting. Lightly cover seeds with 1/8-1/4 inch of soil, as they need some light for germination. Space plants about 10 inches apart for good airflow and healthy growth. Keep the soil moist but not waterlogged during germination.

Cosmos prefer well-draining, light soil and do well even in poor soil conditions. Water moderately, allowing the soil to dry out between waterings to prevent weak, leggy stems. Too much nitrogen will result in excessive foliage instead of flowers, so be careful not to over-fertilize. Plants in windy areas might need staking.

• 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 seeds 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.