Marigolds Tagetes spp. are an annual in most parts of the country, except in the United States Department of Agriculture (USDA) hardiness zones 9-11. Annuals are plants that complete their entire life cycle in one season and then die when temperatures reach below freezing. Hundreds of varieties of marigolds have developed over the years. These plants were originally brought to Europe in the 16th century, where new cultivars were being developed.
There are three main types of marigolds; French, African and Triploid.
The French marigold is a smaller bushy plant that grows to be 6 to 12 inches tall. The flowers are organized in a dense arrangement of "rays" that come in yellow and orange. They grow 2 inches in diameter and bloom continuously all summer long.
The African marigolds, also referred to as American marigolds, are taller and can grow to 3 feet in height. The flowers are bigger and don't bloom as long as the French variety.
The Triploid marigolds are a sterile hybrid of the other two types. This type blooms nonstop, with 3-inch diameter flowers in the warmer colors of gold, yellow and red.
The marigold was first discovered in Central America in the 16th century. The Portuguese first introduced the flower to Europe and India. Marigolds are now widely cultivated in parts of India.
Marigolds were also well known and valued by the peoples of South Asia. Their color was considered similar to the Arya, an honorable people of the region. They were used in special ceremonies.
Marigolds are easy to care for and grow. They do well in full sun or part shade in hot summer areas. They do not need a lot of water unless the weather is hot and dry, in which case they need to be watered plentifully to keep the leaves from becoming too hot in the sun. Overhead watering should be avoided; watering at the root is recommend to avoid blossom rot. Faded flowers should be deadheaded to help prolong blooming and improve appearance.
Marigolds have many uses in the gardens and as container plants. They grow well in window boxes that face south, southwest or west. The smaller varieties combine well with other flowers such as geraniums or petunias. Marigolds also work well in garden beds and borders, because they grow well with other plants and can even be planted to help deter insects from invading other plants and vegetables. Their musky smell works particularly well on nematodes.
Marigolds do suffer from some pest problems, including slugs, snails and aphids.
Slugs and snails feed on marigolds by chewing holes in the leaves and flowers. They leave a slimy mucous trail as confirmation of their presence. For slugs and snails, handpicking can be effective if done carefully and often. They can be drawn out with water and picked off the plants at night with a flashlight. Traps are another control method. They can become trapped beneath boards or flower pots. Wood traps can also be used.
Aphids pierce stems, leaves and tender parts of marigolds to suck out the fluids. Small numbers of them are not too damaging on most plants. If they appear in greater numbers, then leaf curling, yellowing and stunting can occur. They can also transmit diseases from one plant to another. Aphids rarely kill a mature plant, but they cause damage and leave an unattractive honeydew that is generated by their chewing. There are natural control methods, such as predator bugs that eat aphids. Other natural methods include knocking them off with a strong spray of water. Washing the plant with insecticidal soap, water and dish soap can kill them, too. Chemical applications are an option, but check with a garden center or local expert first.