To bloom well, they need at least 6 hours of direct sun each day. With less sun, the blooms will be sparse. If the soil isn't already well-drained, be sure to incorporate lots of coarse organic matter to improve the drainage. Marigolds don't require much fertilizer so feed them every few weeks with a water-soluble such as Bachman's Mighty Bloom . If you want to use dry organic fertilizer, a single application early in the growing season will be enough.
Marigolds can be attractive to slugs and spider mites.
If you experience problems with either of these pests, check our information sheets on those subjects for specific control suggestions. Some of the varieties with extremely large double flowers can have problems with botrytis ruining the blooms during humid weather. Almost all marigolds will need to be deadheaded during the growing season. Deadheading is removing the fading flower heads before they go to seed. By deadheading, you divert the plants energy from setting seed to producing more flowers.