Marigolds are annuals common in the home garden. They are propagated from seed, which can be obtained from most garden centres, or you can harvest them from your garden. Note, though, that harvested marigold seeds are not always duplicates of the parent plants. Also, while you can plant marigold seeds directly outdoors in the garden when frost is no longer an issue, planting them earlier indoors results in early, spring blooms.
Harvest marigold seeds, if necessary. Wait until the flower heads dry out and clip the entire flower. Rub the seed heads with your fingers to release the seeds. Lay the seeds in a single layer on a tray to dry for a day or two. Separate the chaff with a screen, or separate it out by hand. Store marigold seeds in a paper envelope in a cool, dry area until spring.
Start marigold seeds indoors four to six weeks before you expect the last frost of the spring. Use seed trays or peat pots to plant your seeds, using a medium labelled for starting seeds. You can also use perlite or vermiculite as a potting medium. Plant two or three seeds per section, 1/4 inch deep. In a large tray, plant two or three seeds every six inches.
Water the marigold seeds so the soil is slightly moist and maintain moist soil conditions. In seven to 14 days, the marigold seeds should germinate. In three days move them to a sunny location.
Thin marigolds to one plant per seed tray, or one plant every six inches. As they grow, you may need to replant them individually in 3-inch pots. After the last frost, transplant the young marigold plants outdoors in a sunny location, spacing them 18 inches apart.