Marigolds are often the subjects of garden lore, believed to keep both insect pests and nematodes away from homes and vegetable patches. Marigolds used in these plantings tend to be African or French -- both types have annual life cycles. Even though bedding marigolds will not survive the winter except in the warmest of climates, other members of the genus Tagetes have perennial life cycles. These perennial marigolds will survive mild winters and return year after year.
Annuals and Perennials
Plants have evolved a variety of strategies to preserve their species through inclement weather. Perennials go into a state of suspended animation, dropping their high-maintenance parts such as leaves and flowers. Sometimes these plants die back to the ground level and re-sprout from their roots and crown when conditions improve. Annuals, on the other hand, have a short life cycle -- they grow, mature and reproduce within a single growing season. Often bedding annuals self-sow, making them appear to exhibit perennial-like growing habits. However, the plants that emerge when conditions are right are not the same as the parent plants.
Two species dominate the world of bedding marigolds, T. erecta (African marigold) and T. patula (French marigold). French marigolds are small, bushy and compact, growing less than 18 inches tall. African marigolds are significantly bigger marigold plants, reaching up to about 3 feet in height with 5-inch flowers. Another group, the triploid hybrid marigolds, are crosses between these two types. Triploids are sterile, but will bloom repeatedly throughout the season. They cannot self-sow.
Marigolds are native to Mexico and Central America. Several perennial forms have evolved in these areas that are used in folk medicine and as culinary herbs. T. campanulata (canyon marigold), T. mulleri (shade-loving marigold), T. nelsonii (Mayan marigold) and T. parryi (limestone-loving marigold) are common sights in both their native homes and throughout the Southwestern United States.
Extending Annual Marigolds
Few areas in the U.S. can sustain marigolds through the winter, but marigolds grown in extreme parts of Florida have been known to overwinter. These plants still have short life-cycles -- they cannot be expected to live significantly longer than their northern counterparts even when taken inside or raised in a greenhouse. However, if you grow old-fashioned varieties of your favorite marigold species, you can replant new marigolds from the previous season's seeds. Rotate marigold plantings on a three-year schedule for the best results.
- Ohio State University: Marigolds: A Gardening Favorite Year After Year
- Purdue University: Novel Annual and Perennial Tagetes
- University of Idaho Extension: Marigold
- Iowa State University Extension: Marigolds
- North Dakota State University Extension Service: Questions on Marigolds
- University of Missouri Integrated Pest Management Program: The Marvelous Marigold
- Texas AgriLife Extension: Annual, Perennial, Biennial?
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