Cosmos seed should be sown directly in the garden after frost.

• Direct sow seeds in average soil in full sun after danger of heavy frost.
  
• Select a location in full to part shade with good rich well-drained organic soil protected from wind.
  
• Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
  
• Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.
  
• Sow seeds 4 inches apart and ¼ inch deep
  
• Firm soil lightly, water and keep evenly moist.
  
• Seedlings will emerge in 7-10 days.
  
• Thin plants to stand 8-10 inches when seedlings are 1 inch high.
  
• Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. 
  
• Mulches also help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
  
• Keep soil evenly moist but not wet.
  
• After plants are about 6 inches tall, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer such as Flower-tone, as higher rates may encourage root rots.
  
• Tall cultivars may need staking to prevent their thick, hollow stems from breaking due to heavy rain or wind.
  
• Pinch off spent flowers to encourage continuous bloom. Pinching stem tips can reduce height and encourage branching but isn’t necessary. Deadheading is recommended since it lengthens the bloom season. Cosmos plants that aren’t deadheaded will self-sow in warm regions.
  
• Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
  
• Remove plants after they are killed by heavy frost in fall to avoid disease issues the following year.
  
• Cosmos plants can withstand heat and drought conditions.
  
• Tall cosmos add a soft, airy touch to the back of an annual or mixed border. You can also use them as a fast-growing annual hedge or in a cutting garden. Since the taller cultivars are not always uniform in height, they’re perfect for adding an informal look to cottage gardens. Shorter cultivars of both species are ideal near the front of the border, in containers, or as edgings.
  
• Cosmos makes beautiful cut flowers.
  
• Because cosmos is easy to grow and the seeds are large and easy to handle, it is a good choice for a children’s garden.