Prepare a location for planting that has 2 inches of compost spread over and tilled in 8 to 12 inches. The site must be in full sun, as marigolds prefer six to eight hours of sun per day.
Plant seeds when all danger of frost is over and the temperatures reach about 70 degrees Fahrenheit during the day. Plant the seeds by making a slight indentation in the ground using a trowel. Place the seeds in the indentation and cover with 1/4 inch of soil.
Water lightly after planting and keep the soil moist, but not soggy. Germination takes place in a few days.
Thin seedlings to eight inches apart for smaller French marigolds and 18 inches apart for large African varieties. The flowers will bloom 45 to 50 days from planting seed.