Can the seed gathered from deadheading be used again?
Deadheading means to remove the wilted flowers before they ripen with seeds. The object is to get the plant to invest its energy into making more flowers, instead of producing seeds. If you allow a few of the flowers to wilt, dry, and fall of naturally, you will have seeds aplenty for next year. Many people allow one or two plants to produce seed, and deadhead the others to get the most flowers. Here's an article with more information: https://www.gardeningknowhow.com/ornamental/flowers/marigold/growing-marigold-flowers.htm