Plant marsh marigold in early spring in a location with full sun to partial shade. Ensure the soil is consistently moist or even waterlogged, as this plant thrives in wet conditions. Space plants about 12-18 inches apart. Water regularly to maintain soil moisture, especially in drier periods. Fertilize with a balanced, water-soluble fertilizer in early spring. Deadhead spent flowers to encourage more blooms. Divide clumps every few years in early spring to maintain vigor.