Marigolds thrive in full sunshine and can often withstand very hot summers. African and signet marigolds are drought tolerant, while French marigolds are more tolerant of wet conditions. If planted in shade and cool, moist areas, marigolds are prone to powdery mildew and won’t bloom well.

Planting: 

Though they grow in almost any soil, marigolds do best in moderately fertile, well-drained soil. Prepare the soil by digging down about 6 inches to loosen it, then mix in compost to add fertility and improve consistency.

• Sow seeds directly into the garden. You can start seeds indoors, but they germinate so easily outside that there’s really no advantage. The exception is African marigolds, which are best bought as young plants or started indoors about 4 to 6 weeks before your last frost date.
• Marigolds sprout within a week in warm weather and plants typically produce blooms in about 8 weeks.
• Moisten the soil, then sow seeds 1 inch apart and no more than 1 inch deep.
• While still small, thin the seedlings. Larger African marigolds should be at least 10 to 12 inches apart.
• If planting transplants, thoroughly water each plant after planting in the garden.
• If planting in containers, use a soil-based potting mix. Either mix in slow-acting granular fertilizer at planting time or plan to water with diluted liquid fertilizer periodically. Take care to space properly; marigolds grown in containers can become crowded.

How to Grow:

• Once the marigolds have established themselves, pinch off the tops of the plants to encourage them to grow bushier. This will keep the plants from becoming leggy and will encourage more blooming.
• Marigolds don’t require deadheading, but if dying blossoms are regularly removed, it will encourage the plant to continue blooming profusely.
• When you water marigolds, allow the soil to dry somewhat between waterings, then water well and repeat the process. Water more in high heat.
• Do not water marigolds from overhead. Water at the base of the plant. (Excess water on leaves can lead to powdery mildew.)
• Do not fertilize marigolds during growth. A diet that’s too nitrogen-rich stimulates lush foliage at the expense of flowers.
• The dense, double flowerheads of the African marigolds tend to rot in wet weather.
• Add a layer of mulch between plants to suppress weeds and keep soil moist, especially when plants are young.
• Deadheading marigolds is very simple. When a blossom starts to go bad, pinch (cut) its stem back to the nearest set of leaves.