Cosmos bipinnatus. Reliable and well-loved single daisy shaped flowers with yellow centers bloom in white and various shades of pink. Pinching off the growing tip when the plant is about 15cm (6") tall will help keep this tall lacy plant bushy and erect. Do not overfeed, as rich soil will delay flowering. Sensation Mix cosmos seeds plant height 1.2-1.8m (4-6'). Stake these tall Cosmos in windy gardens, but in sheltered areas, this is not necessary. Deadhead (remove spent flowers) to extend the flowering period and keep plants looking their tidiest. Cosmos is quite drought tolerant so it makes a good candidate for xeriscaping. Provide some water in extreme drought. Sensation Mix won an AAS Award in 1936.
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. Cosmos seeds are easy to harvest and save. These annual plants are sometimes referred to as Cosmea. Continue reading below for tips on how to grow Cosmos from seed.
Cosmos bipinnatus & C. sulfureus
Season & Zone
Exposure: Full sun
Direct sow after the last frost date. Several sowings will result in a very long bloom period. Cosmos can also be started indoors in late winter for transplanting after last frost, once daytime temperatures are above 10°C (50°F). Seeds will sprout in 3-10 days. Optimal temperature for germination: 21-25°C (70-75°F).
Sow seeds very shallowly only a few millimetres (1/8″) deep. Thin or transplant to 20-25cm (8-10″) apart.
Most varieties can get quite tall, and in exposed or windy gardens can benefit from staking or trellis netting laid horizontally over the bed for the stems to grow through before blooming. Deadhead and cut for bouquets regularly to extend the bloom period.