It is best to plant them in a sunny spot and into soil which has some organic material, such as Farmyard Manure, dug into it.
This will help them to retain water.
They should be planted 30 to 45 cm (12-15 inches) away from each other to allow for bushy growth.
Cosmos can be grown indoors, Space plants 6–9” apart.
If you are using supplemental lighting, apply long day treatment (14 hours or more of light per day) until plants have approximately 6 leaf pairs or until the stems are of adequate length.
Cosmos prefer full sun conditions, except in extreme heat where they can tolerate part shade.
Soil, Prepare the garden with loose, weed-free soil. Cosmos prefer dry, arid soil over wet conditions. Soil that is too moist may lead to disease.