Fill small seed-starting pots or flats with a sterilized potting mix to within 1 inch of the container's rim. Use containers with drainage holes in the bottom.
Sow three seeds per pot or sow in a grouping of three spaced 3 inches apart in seed-starting flats. Sow on the soil surface and cover with 1/4 inch of vermiculite.
Water the soil until evenly moist throughout. Cover in plastic wrap and place in a warm room to germinate. Germination takes approximately 5 to 7 days.
Remove the plastic wrap once seedlings appear. Place marigold seedlings in a warm, sunny window or under grow lights. Keep soil moist at all times.
Transplant marigolds outside or to their permanent containers once the last expected frost date for your area is past. Choose a well-draining bed in full sun and add 1 tsp. of general fertilizer per square foot at planting.