Plant French marigolds 6 to 9 inches apart and African marigolds up to 18 inches apart. Keep a close check on water during the first 10 to 12 days. After that, water thoroughly once a week if it has not rained at least an inch that week. Remove the old flowers as they fade for continued bloom. Tall marigolds may require staking to prevent the plants from falling over during storms.
Spider mites can be a problem in hot, dry weather.
Aster yellows and fungal stem and root rots are occasional disease problems. Some gardeners plant marigolds in their vegetable gardens to repel harmful insects. Studies have concluded they are not effective in reducing insect damage on vegetable crops. French types may be useful for root-knot nematode control in soil. These marigolds have large, double flowers from midsummer to frost.