No annual is more cheerful or easier to grow than marigolds. These flowers are the spendthrifts among annuals, showing a wealth of gold, copper, and brass into our summer and autumn gardens. The flower’s popularity probably derives in part from its ability to bloom brightly all summer long.
Marigolds need lots of sunshine. Though they grow in almost any soil, marigolds thrive in moderately fertile, well-drained soil. Sow them directly into the garden once the soil is warm, or start seeds indoors about a month to 6 weeks before the last spring-frost date. The seeds germinate easily, but watch out for damping off if you start them inside. Separate seedlings when they are about 2 inches tall. Plant them in flats of loose soil, or transplant them into the garden. Space tall marigolds 2 to 3 feet apart; lower-growing ones about a foot apart. If planting in containers, use a soil-based potting mix.
Germination from large, easily handled seeds is rapid, and blooms should appear within a few weeks of sowing. If the spent blossoms are deadheaded, the plants will continue to bloom profusely. When you water marigolds, allow the soil to dry somewhat between watering, then water well, then repeat the process. Do not water marigolds from overhead. Water at the base of the plant. Do not fertilize marigolds. Too rich a diet stimulates lush foliage at the expense of flowers. Marigolds bloom better and more profusely in poor soil. The densely double flowerheads of the African marigolds tend to rot in wet weather.
Farmers and gardeners have long known that marigolds make important companion plants all over the garden. Not only does the scent of the marigold (Tagetes spp.) repel animals and insects, but the underground workings of the marigold will repel nematodes (microscopic worms) and other pests for up to 3 years.