March 2010 - Marigolds

HISTORY

Marigolds are native to the Americas from Argentina north to New Mexico and Arizona. The earliest use of marigolds was by the Aztec people who attributed magical, religious and medicinal properties to marigolds. The National Garden Bureau found the first recorded use of marigolds in the De La Crus-Badiano Aztec Herbal of 1552. The Herbal records the use of Tagetes lucida for treatment of hiccups, being struck by lightening, or “for one who wishes to cross a river or water safely.” The last use confirms the magical properties ascribed to Tagetes.

The Aztecs named their native flower, cempoalxochitl, and bred it for increasingly large blooms. It is suspected that in the 1500’s, native marigold seeds were taken from the Aztecs by early Spanish explorers to Spain. The marigolds were cultivated in Spain and grown in monastery gardens.

From Spain, marigold seeds were transported to France and northern Africa. The taller marigolds, now called African or American, became naturalized in North Africa.

During a 1535 expedition to Tunis, the tall naturalized marigolds were observed and mistaken for native wildflowers. Seed was collected and once again taken to Spain. The newly collected marigold was named Flos Africanus due to its mistaken origin. The tall marigolds were widely known by that name well into the 1700’s. This was a classic case of error in origin.

The name Tagetes has unusual origins as well, tracing back to the revered Italian god, Tages. A grandson of Jupiter, Tages came forth from a clod of earth as a wise and handsome boy. So the American native marigold is commonly called French or African but the genus name Tagetes refers to an Italian god.

Marigolds figure prominently in many religious ceremonies. In Mexico and Latin America, marigold flowers are used to decorate household altars to celebrate All Saints Day and All Souls Day. Flower heads are scattered on relatives’ graves, which can account for the profusion of marigolds in cemeteries.

Marigolds are also used in Hindu religious ceremonies. The National Garden Bureau’s research found the Indian “gendha” to be the T. erecta species. An account in 1963 describes the marigold being used as garlands to decorate village gods during the harvest festival. The traveler recalling the festival also noted the maize and peppers were exactly the same shade of orange-yellow as the marigold. It was as though the corn and peppers were selected or bred to match the marigold flower color. “Gendha” is also reported to be used as a yellow cloth dye in India and Pakistan.

Several hundred years after their initial journey from the Americas to Europe and Africa, marigolds were introduced to North American gardeners. This reunion of sorts did not happen until shortly after the Revolutionary War. Marigolds were just one of many plants shipped to the young country.

Around the turn of this century, sweet peas and asters were the most popular flowers in the United States. Yet both of them were becoming beleaguered by disease and declining overall performance. The time was right for a ‘new’ flower to make its debut. In 1915 David Burpee took over the seed company, which was founded by his father, Washington Atlee Burpee. Young David felt that marigolds held promise and decided to feature them in his catalog and fund research.

Since the 1920’s marigold breeding has developed hundreds of new varieties. The odorless marigolds, hybrids and triploids have all been advancements in breeding. In the last thirty years most of the research, new varieties, and seed production has been accomplished by American breeders and seed companies. Somehow it seems fitting that the marigold would find the breeding emphasis and popularity back in the Americas, its center of origin.


AAS 1959 Petite Gold	AAS 1999 Bonanza Bolero	AAS 1968 Orange Jubilee	AAS 1979 Queen Sophia

NOMENCLATURE

The genus Tagetes contains 40 species. All are native to the New World with the greatest diversity being found in south central Mexico. Three species have been chosen for research and cultivation as ornamental plants. They are:
T. erecta – commonly called African or American.

T. patula – commonly called French marigolds in spite of American origin.

T. tenuifolia – Signet marigolds, unusual lacy leaves with small single flowers.

A fourth species, T. filifolia or Irish Lace, is not widely grown or known. It is planted for the foliage rather than flowers.

In the plant kingdom, other flowers have had the word marigold added to their common name. This adds to the confusion of the marigold species. Plants such as Caltha palustris, commonly called marsh marigold and Calendula officinalis, L. pot marigold or cape marigold are not within the Tagetes genus; the focus is placed on T. erecta and T. patula. These two species are the origins of most modern day garden marigolds.

Tagetes patula, L. the “French marigold”

This dwarf, compact plant species contains the widest color range of marigolds. The flowers can be pure or solid orange, yellow, gold or mahogany red. The color diversity expands with bicolors meaning two colors per flower. Bicolors such as orange and gold, mahogany red and yellow offer a spectrum of color combinations. Petals can be edged with a contrasting color or the color can be placed at the petal base. A clue to identification can be noted here. If you observe a mahogany red bloom, it is a French marigold. The mahogany red color is not available in the T. erecta, L. species.

The French marigold flower form has been divided into five distinct types. The single flower form is the easiest to identify. There are five or eight overlapping petals in a single layer. These are called ray petals. There is a small central disc or tuft of stamens and pistils, the reproductive plant parts.

The anemone flower form contains broad, flattened petals, again overlapping. There are more rows of petals surrounding the central disc and are described as semidouble. The anemone flower form has recently received attention from many breeding programs.
The carnation flower form or fully double has numerous rows of overlapping petals. There can be a small central disc. This was the most common French marigold flower form in the 60’s and 70’s.

The crested flower form is subdivided into double and single crested. The crest or central disc petals are the dominant feature in either flower form. The center contains numerous short petals tightly clustered. Surrounding this crest are the ray petals, broader and flatter. If there is only one row of ray petals surrounding the crest it is considered a single crested flower form. If there are three or four rows of ray petals, it is a double crested French marigold. There have been many recent introductions in the double crested form. At this time there are no hybrid French marigolds.

In the garden, the T. patula marigolds are considered dwarf French. They range in height from 6 to 14 inches when mature. A gardener can choose from 1 inch to 2-1/2 inches for flower size. This species is the most popular of all marigolds. Easy to grow under most weather and soil types, French marigolds are reliable annuals.

Tagetes erecta, African or American Marigolds

This species is characterized by larger leaf size and larger flowers than T. patula. The flower forms are either semidouble or fully double. The semidouble flowers have fewer rows of ray petals than fully double. The size of the flower is the dominant feature. A small flower is 3 inches across. The larger flowers are 3-1/2 to 4-1/2 inches. The colors are solid, no bicolors occur in this species. The color range is from white and cream to primrose, yellow, gold and orange. There are many F1 hybrid T. erecta cultivars available to home gardeners. Since they are hybrids, they express hybrid vigor by producing numerous flowers on uniform plants with a long flowering season.

Due to the height, most gardeners place T. erecta in the back of a bed or massed in an individual planting area. The plant height at maturity can be 9 inches for a dwarfer variety. The height can be from 9 to 28 inches. The tallest varieties attain a height of 38 to 40 inches and also have longer flower stems suitable for cutting. The T. erecta marigolds are versatile. Fewer plants are required in a garden bed to create the desired result, lavish annual color. Space the plants further apart, 12 to 18 inches or more depending upon the mature height. The marigold plants will fill in the space between them.

T. erecta species are day length sensitive. Each cultivar varies in the response to day length. If a home gardener is growing T. erecta from seed sown after March 1 and wants earlier flowering plants, a short day treatment can be applied. Just cover small seedlings with a light proof cover at 4:00 p.m. and remove at 8:00 a.m. This treatment can be applied for two weeks.

Triploids or 3-N Hybrids

T. erecta x T. patula. This is a wide cross between the African (American) and French species. The cross between species results in a plant that is sterile, unable to reproduce. Since the triploid is not capable of setting seed, the plant produces more flowers. This characteristic is significant when compared to T. patula. Most T. patula plants will decrease flowering under hot summer temperatures. It is called heat stress and shy blooms are the result. The triploid marigolds are not subject to heat stress and continue blooming prolifically regardless of the heat. The triploid blooms are 2 to 2-1/2 inches. Mature garden height can be 10 to 16 inches. The flower form on triploids can be single, double or semidouble. The color range is similar to T. patula with solid colors and bicolor designs. The triploid seed germination is less than the T. patula germination. The first triploid marigold was introduced in 1939. There have been many triploids introduced, improvements in flower size and compact plant habits. Triploids are capable of literally covering the plant with blooms.


AAS 1968 First Lady	Disco Red	AAS 2010 Moonsong Deep Orange	Discovery Yellow

HOW TO GROW MARIGOLDS

Marigold seeds are large, easy to handle and germinate reliably in warm, moist soil. T. patula can be sown directly on garden soil after the soil has warmed to 70ºF. Soil should be tilled so that it drains and has a fine, loose texture. Dig a furrow about two inches deep with the corner of a garden hoe. Water the furrow slowly to soak the soil. Scatter seeds in the furrow about an inch apart. Cover lightly with dry soil, sand, or vermiculite. Water again with a fine mist. Continue watering daily with a fine spray for 10 to 14 days when seedlings should appear. As seedlings grow, water less frequently but apply more water to encourage deep root growth. The T. patula seedlings can be transplanted when small to other garden locations. If garden soil is fertile and rich in organic matter, supplemental feeding might not be necessary. Overfeeding or a rich organic soil can result in vegetative growth and a lack of flowering. T. patula will flower in 6 to 12 weeks from sowing, depending upon variety and weather conditions.

T. erecta marigolds are best started indoors and transplanted into the garden. Sow seeds eight weeks prior to planting outdoors in warm garden soil. Cover seeds lightly and maintain uniform moisture. Transplant into larger containers at the 3 to 4 true leaf stage. Provide as much direct sunlight as possible while indoors.

DISEASES

The National Garden Bureau found two diseases that might infect marigolds in gardens. These two are aster yellows and botrytis, the most common problems encountered by North American gardeners. Many gardeners will not encounter any problems or diseases with marigolds. The marigold aroma, produced by oil glands on the undersides of leaves, is thought to repel some harmful insects. Thusly, marigolds are one of the most reliable annuals any gardener can grow for summer color and durability.

Aster Yellows

As the name indicates, this disease affects asters and marigolds as well as many other garden flowers. The disease is spread by six-spotted leafhoppers, which become infected by feeding on infected weeds. The leafhoppers spread the disease as they feed. The higher the number of leafhoppers, the higher the chance of plant infection.

The symptoms include a yellowing of the foliage, pale greenish yellow abnormally shaped buds and blooms, and an overall stunting of the plant. A diseased plant stands out from among healthy ones by its lack of flowers and oddly shaped plant. By the time the buds and blooms become misshapen, there is no alternative but to remove the plant. The only control over this disease is to control the population of leafhoppers, an unlikely solution at best.

Botrytis
This fungus, Botrytis cinerea, thrives in cool, moist conditions attacking injured tissues, dying blooms or foliage. The fungus is a mold that produces masses of gray spores that are spread by wind or water. Botrytis usually affects double marigold blooms late in the growing season when heavy dew and cool temperatures create the perfect environment for this fungus growth. It appears as brown, dying tissue at the base of the flower petal. If allowed to grow, the fungus can spread rapidly to infect healthy plants. The best control is to remove spent flower heads from the plant. This is particularly important near the end of the growing season.


Marigolds	AAS 1972 Gold Galore	AAS 1989 Golden Gate	Taishan Yellow

MARIGOLDS AND NEMATODES

Nematodes are a diverse group of microscopic worms. Some nematodes are beneficial to the soil or plants, others invade or penetrate plant roots and feed on nutrients thereby robbing the plant of them. Some of the harmful nematodes can be reduced by marigolds growing in the soil. Recent scientific studies have shown that chemical compounds produced by most Tagetes are toxic or antagonistic to certain harmful nematodes. Evidence suggests that the chemical compounds are toxic to nematodes both upon entry into the root system or in the vicinity of the roots. The National Garden Bureau concludes that Tagetes contributes to the control of harmful nematode pollutions in garden soil.

CONTAINER GARDENING

Marigolds adapt well to container gardening. Remember to match the mature plant size to the container size. The T. patula French marigolds can be grown in smaller containers due to their smaller plant size. One French marigold will fill a 6-inch pot. French marigolds can be planted with vegetables in the same container. Combining various cultivars requires more attention to the water and fertilizer needs of the plants. French marigolds will thrive in larger containers such as wine barrels, urns, or redwood planters. One consistent rule for all container gardens is to ensure that water drains from the soil. Use containers with holes on the bottom or sides.

Both T. tenuifolia, signet, and T. erecta, African or American marigolds can brighten any patio with bold color grown in containers. Signet marigolds require a 6 to 10 inch container while the African or American needs more space and soil. Use a 12 to 15 inch diameter container at least 18 inches deep for the mid height range T. erecta.

FUTURE BREEDING

America continues to lead in the breeding advancements of marigolds. The two Tagetes species receiving the most breeding and research effort continue to be the T. patula, French and T. erecta, African or American. Breeders are selecting marigolds for earlier flowering with specific improved characteristics such as increased flower size. The single marigold flower form has been given recent attention with several new varieties introduced. Crosses between species such as the T. patula x T. erecta or triploid marigolds will continue to be improved for germination and seed vigor. Someday, breeders will be able to introduce the T. patula mahogany red genes into the T. erecta species for huge 3-inch red blooms. Or the reverse, introduce the white T. erecta genes into a dwarf French marigold. The National Garden Bureau is confident the breeders will continue to select marigolds that will find a featured position in America’s gardens. Whether tall or short, single or double flowered, marigolds will flourish across North America.