Marigolds only need enough water to dampen the soil, and they only require watering about once every ten days. The soil should be allowed to dry out on the surface before watering. The base of the plant should receive the water, and the plant should not be watered from overhead.
Wetting marigolds from overhead causes the blossoms to become soggy. This can cause the flower to brown and could kill the blossoms.
Marigolds do not need to be fertilized. In fact, too many nutrients are detrimental to the look of the plant. It causes less flowers to grow and more foliage.