Easy to grow from seed, marigolds (Tagetes spp.) grow well during the warm months of the year when there is no danger of frost. While the leaves of marigolds are fernlike and smell pungent when crushed, gardeners mainly grow marigolds for their large, waxy yellow-orange or rusty-red flowers, which make excellent cut flowers.
Four primary types of marigolds are grown in the United States. Marigolds tend to bloom only when their stems approach their mature heights. The small marigolds are French marigolds (Tagetes patula), which mature as 6- to 12-inch tall bushes. The upright, taller marigolds are African or American marigolds (Tagetes erecta), growing 24 to 48 inches tall. Triploid or hybrid marigolds are genetic crosses of French and African types, yielding mid-sized plants and flowers. Signet or Mexican marigolds (Tagetes tenuifolia) bear five-petaled flowers on bushy plants 12 to 18 inches tall with needlelike leaves.
Lovers of Sunlight
Planting marigolds in lots of sunshine ensures the fastest growth, earliest production of blossoms and highest number of flowers. Place marigolds where they receive no less than eight hours of direct, uninterrupted sun daily. Marigolds will grow in poor light, but they become primarily leafy plants, with diminished or no flowering.
Unhealthy or weakly growing marigolds don't bloom very well, if at all. Marigolds need a fertile soil that is moist but well-drained. Overwatering the soil to keep it soggy leads to root and stem rot. Foliage and flower heads that remain wet also tend to quickly rot and drop away. Do not plant marigolds in soil that always puddles or floods after rains. Moreover, do not plant them in sandy, nutrient-deficient, dry soils as that limits plant growth.
Frost kills marigolds. They also grow slowly when soil and air temperatures are not summerlike. When first planted in spring, the cooler weather inhibits fast growth and production of flowers. Once temperatures get above 75 degrees Fahrenheit and nighttime temperatures remain in the 60 to 70 degree range, growth and flowering hastens. Full sun exposures provide the fastest warming of the garden. In years when spring and summer weather is unusually cloudy and rainy, it may take marigolds several more weeks to finally be large enough to bloom.