Cosmos bipinnatus. Purity cosmos seeds yield single snow-white flowers to lighten the dark areas of a cottage garden. Regular dead heading will encourage continuous flowering from summer into late autumn. The ferny foliage on this variety is graced by the flowers up to 10cm (4") in diameter on plants that grow to about 76cm (30") tall. Stake this variety if growing in exposed areas, or use Green Garden Netting to keep plants upright. When they are just two feet tall, let their tips grow through a layer of netting lain flat over the bed. This will give them all the support they need.
Cosmos will flower more in poor soil, rather than rich, so avoid manures and fertilizers. Pinch out the growing point when plants are around 45cm (18″) tall to encourage bushier growth and more flowering points. Water during very dry spells, but otherwise, Cosmos is well suited to xeriscaping. Seeds are easy to harvest and save.
These annual plants that are sometimes referred to as Cosmea.
Cosmos bipinnatus & C. sulfureus
Season & Zone
Exposure: Full sun
Direct sow from early March right up until mid-June. Several sowings will result in a very long bloom period. You can also start Cosmos indoors in February to early March for transplanting late March to mid-April. Seeds will sprout in 3-10 days. Optimal temperature for germination: 21-25°C (70-75°F).
Sow seeds very shallowly only a few millimeters (1/8″) deep. Thin or transplant to 20-25cm (8-10″) apart.