To grow marigolds, place them in a location with full light, use well-drained soil, give them plenty of room to grow, and deadhead faded flowers. Marigolds require regular watering.
First, choose a gardening site where the plant is exposed to full sun for best blossoming. The site also needs poor to moderately fertile soil. Because rich soil encourages foliage rather than flower growth, don't add compost or fertilizer to the soil. Use well-drained soil or potting mix as moist soil can cause root rot.
Either start marigold seeds indoors, or plant them outside after the last frost once the soil warms up sufficiently. After sowing the seeds, thin the seedlings out until the marigold plants are between 1 to 2 feet apart depending on the variety. Low-growing marigolds can be placed closer together.
Water the plants well whenever the soil starts to dry out from the base of the plant, but avoid wetting the foliage. If the soil is too wet or the foliage stays damp, the plant can develop a number of diseases due to damp conditions such as root rot, damping off, gray mold and powdery mildew. Once the flowers begin to fade and wilt, snip them off to encourage flowering.