Causes of a Flowerless Marigold

Growing Conditions

• Marigolds grow best in average garden soil with partial or full sun. Damp, shady conditions inhibit flowering. During the hottest days of summer in full sun, flowering may slow or stop but will resume when the weather moderates. Protect marigolds from direct afternoon sun in planting zones 7 through 10. If your marigolds have lush foliage but no flowers, stop fertilizing the plants. Apply a single dose of slow-release fertilizer at planting time only.

Pests

• Despite its use as a pest repellent companion plant, marigolds are attractive to a variety of destructive insects. The Japanese beetle, a shiny, copper-colored iridescent beetle about 1/2 inch long, chews marigold leaves and flowers. Leafhoppers damage and wilt foliage, a condition that inhibits flower production. Look for small brown insects and rolled foliage. The tarnished plant bug sucks plant juices from and injects a poison into the stem and flower buds. Buds drop off or form deformed blossoms.

Fungal Diseases

• Several plant diseases strike marigolds. Often, it is the foliage that shows the most damage but diseases effect the overall health of the plant and may reduce or prevent flowering. Botrytis blight is a contagious fungal disease. Soft gray spots develop on the flower scales and plant stems and the plant may die back. Other fungal diseases include leaf spot, fungal wilt and stem rot. Dig up and destroy affected plants -- do not place them in the compost.

Care

• French marigolds flower 45 to 50 days after seed germination so most gardeners start seeds indoors in early spring or purchase established seedlings. For the earliest and longest-lasting blooms, set out robust, flowering seedlings after the danger of frost has passed. African marigolds -- Tagetes erecta -- do not bloom all summer. These large annual marigolds produce foliage through June and July and bloom in late summer. Pinch off dead marigold flowers to encourage new blossoms.