Tagetes or marigold is a plant genus of approximately 50 species in the Asteraceae sunflower family; they are originally from the Americas, although they are naturalized everywhere now. Carl Linnaeus classified the genus in 1753. Most of the plants commonly cultivated these days originate from three species – T. patula, T. erecta, and T. tenuifolia.
The plants in this species come in sizes ranging from 4-36 inches high and 6-18 inches wide with mostly green pinnate leaves and fibrous roots. Flower colors come in yellow, gold, orange, white, red and bicolored and typically span 1.5-2.5 inches, with disc and ray florets. They generally grow as annuals, although perennial species are now gaining popularity. These plants easily grow every year either by self-seeding or from the stems sprouting from existing plants.
The foliage of most species has a pungent, musky scent, although some scentless varieties have been developed. These plants are reputed to deter some insect pests, including nematodes, and are frequently utilized as companion plants grown alongside eggplant, tomato, chili pepper, potato, and tobacco. In contrast, the roots of these plants exude antibacterial thiophenes and shouldn’t be planted close to legume plants. A few perennial species are also rodent-, rabbit-, deer- and javelina -resistant several insects such as butterflies, honey bees, and bumblebees extract nectar from these plants, including caterpillars of moths and butterflies who use the plants as a food source. They are also frequently cultivated in butterfly gardens.
T. minuta (huacatay or khakibush), originating from South America, is used to produce essential oil (“marigold oil”) for the perfumery industry and is used as a flavoring in the tobacco and food industries. In South Africa, the plants are cultivated to reclaim land affected by mining activity.
These plants are extensively cultivated in India for their flowers that are sold in markets for decorations and garlands for religious events, weddings, and festivals.
These plants must be grown under full sun to get copious flower production and to keep the plants healthy.
They need water every two days when they are first planted to develop healthy root systems. Once they get established in a few weeks, water them once a week. However, if the weather is very hot, water them every day. Mature plants are somewhat drought-tolerant, but they will flower better with weekly watering. Plants growing in containers might require watering every day.
Try not to get the flowers when watering the plants by just watering the soil. The flowers might become brown and mushy if they get wet. Drooping leaves indicate that the plants need some water. Don’t over-water the plants as they are vulnerable to root rot.
These plants can tolerate high humidity provided they have good airflow, but still may face problems with powdery mildew, particularly with damp and humid summers
These plants can tolerate temperatures of zones 2-11 but they are not frost-tolerant and will die in temperatures below 50°F. Cultivators in most planting zones usually replant them every spring.
These plants can grow in any well-draining garden soil with a soil pH above 6.0. They also tend to thrive in leaner soils rather than soils rich with organic matter.
Since these plants generally don’t live as long as perennials, repotting isn’t needed unless you transplant seedlings from smaller pots. All varieties can thrive in containers, but some of the taller varieties can grow 3 feet high and need larger containers.
Don’t over-crowd potted plants, as healthy plants need lots of air circulation. One plant is acceptable for a 6-inch pot, but two or three (shorter varieties) can be grown in a 12-inch pot. The containers should have good drainage with a lightweight potting mix amended with sand, vermiculite, or perlite to improve drainage.
They are very easy to propagate from seed. Seeds can be started indoors before spring begins but it’s not worth the effort since seeds planted directly in your garden will germinate quickly when the weather becomes warm, and since the seedlings are available in almost every nursery, you can jump-start your garden instantly just transplant the seedling into your garden or prepared containers.
These plants don’t need supplemental fertilizing unless their soil is very poor.
Deadheading spent flowers encourages more flower production throughout their growing season.
When the growing season is ending, allow some flowers to stay on the plant to turn into seeds that can be harvested, dried, and planted in the coming year.
Powdery mildew infection is the most common problem affecting these plants, particularly in humid conditions, leaving powdery white or grey residue on the foliage and stems. However, in severe infections, leaves can get twisted or become yellow. When you spot this powder, spray it off with water, although if you don’t spot it in time, the plants might not survive. Prevent further spread by thinning out the plants to allow air to freely pass between them.
If the leaves of these plants turn yellow, it might be caused by aster yellows. This disease is transmitted by leafhoppers. There is no treatment or cure for this – remove and destroy the plants. Use a suitable insecticide to control and eliminate leafhoppers.
Over-fertilizing can cause leaf burn, making the leaves yellow as mentioned. These plants don’t need to be fertilized – if you have to feed them due to poor soil, dilute the recommended dose by ¼ and water the plants well afterward. Over-fertilizing can also result in more foliage than blooms.
Although these plants don’t have problems caused by too many pests, they can fall victim to some like mealybugs. Treat them with neem oil.
Extremely hot weather can result in less or no flower production as the plants will focus their energy to stay alive. Add mulch to the soil to reduce soil temperature.
Drastic temperature fluctuations can make flowers pale. This will resolve itself once the weather settles down.