Cosmos are plants that have few needs and are very easy to grow. Sowing cosmos can start as soon as the last frosts have passed (April in mild climates), until June.
The tallest varieties can be staked to prevent them from sagging and faded flowers will be removed to encourage the new ones to bloom. Watering in the event of summer drought helps support flowering. If winter temperatures drop below -5°C, consider digging up the tubers of perennial varieties to store them in peat or sand.