It is hard to find a flower that is easier to grow than cosmos. Cosmos seeds simply need to be hand broadcast onto the soil after the last frost. Once planted, they will grow and bloom happily with very little help from you. In fact, it is quite possible to provide too much care for cosmos flowers. If given fertilizer they will grow too quickly, become spindly and produce fewer blooms. And they must only be watered if there has been no rainfall that month.
Till the soil to a depth of 4 inches.
Plant cosmos seeds. Simply hand broadcast them (1 oz. per 10 square feet), then lightly rake them into the soil. Cosmos seeds only need to be planted 1/16 inch beneath the soil surface. If planted any deeper, they may not germinate.
Water your cosmos seeds lightly. Continue to keep the soil moist until they germinate in one to three weeks. After they germinate, cosmos seeds should only be watered if there is no rain for one month. In that case, cosmos flowers should be watered deeply, but only once that month.