Marigold seeds are large, easy to handle and germinate reliably in warm, moist soil. T. patula can be sown directly on garden soil after the soil has warmed to 70ºF. Soil should be tilled so that it drains and has a fine, loose texture. Dig a furrow about two inches deep with the corner of a garden hoe. Water the furrow slowly to soak the soil. Scatter seeds in the furrow about an inch apart. Cover lightly with dry soil, sand, or vermiculite. Water again with a fine mist. Continue watering daily with a fine spray for 10 to 14 days when seedlings should appear. As seedlings grow, water less frequently but apply more water to encourage deep root growth. The T. patula seedlings can be transplanted when small to other garden locations. If garden soil is fertile and rich in organic matter, supplemental feeding might not be necessary. Overfeeding or a rich organic soil can result in vegetative growth and a lack of flowering. T. patula will flower in 6 to 12 weeks from sowing, depending upon variety and weather conditions.
T. erecta marigolds are best started indoors and transplanted into the garden. Sow seeds eight weeks prior to planting outdoors in warm garden soil. Cover seeds lightly and maintain uniform moisture. Transplant into larger containers at the 3 to 4 true leaf stage. Provide as much direct sunlight as possible while indoors.
More information on growing marigolds.
Source: National Garden Bureau.