Gardeners seeking a tall and showy backdrop for a flower garden often turn to the colorful cosmos. With their towering stems and bright, wide blossoms, cosmos will attract bees, butterflies and even hummingbirds to your garden. Because cosmos grows readily in a variety of garden soils, with average or even poor soils producing the best flowers, it can be an ideal addition to any sunny location. The care required for cosmos is minimal, and the flowers reseed themselves easily at the end of each growing season.
Cultivate the growing area in the spring after the soil warms to between 60 and 65 degrees Fahrenheit. Work the soil with the garden spade down to a depth of approximately 6 inches and then smooth the soil surface evenly with the rake.
Sprinkle the cosmos seeds evenly over the soil surface. Seed spacing is not important--simply cover the planting area with seeds.
Rake the soil where you placed the cosmos seeds lightly with the rake to ensure the seeds have adequate contact with the soil.
Provide a light watering over the seeding area immediately after planting the cosmos seeds. Keep the soil surface evenly moist during germination. Watch for the cosmos seeds to sprout within one to three weeks after planting. Provide water for the cosmos flowers if less than 1 inch of rain falls within a one-week period.
Stake the cosmos flowers if they need support. Insert a stake into the soil 3 inches away from the stem and tie the cosmos stem to the stake using one or two plant ties.
Allow the spent blossoms to self-sow if you desire more cosmos flowers in future growing seasons. Leave the spent blossoms on the stems until autumn, and seeds will fall to the ground to produce new cosmos flowers.