Harvesting marigold seeds is an easy way to save yourself the money and hassle of buying new seeds every summer. Each flower produces lots of tiny seeds, so it won't take long to collect enough for a new crop. If you only grow one type of marigold your seeds will produce the same flowers. However, if you grow several different types your seeds may produce hybrids, or any combination of your current marigolds.
Leave flowers on their stems to dry in the garden. Do not deadhead flowers that you want to save for seed. The flowers will wilt and die, and after about a week the petals and shell will turn dry and brittle, and the flower will take on a brownish color.
Remove one or two brown flowers from the stem and break open the shell underneath the dried petals. Inside you will see a bunch of small, straight seeds. If the seeds are dark brown or black, they are mature. If they're not darkly colored, leave the other flowers to dry for a few more days and then check another bunch for maturity.
Remove the rest of the dried flowers by pinching the stem just below the flower's shell between your thumb and forefinger. Bring the flowers inside and leave them in a dry place for one to two weeks to fully dry out. Flowers should be lightweight and brittle, with no signs of moisture.
Open the shells and remove the dried seeds. Collect the seeds in an envelope or small jar, and discard the dried petals and shell. Store your seeds in a cool, dry place until the following spring.