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Marigolds and Greenhouse Crop Production

Greenhouse Crop Production of Marigolds

Growth Habits

The marigold is a perennial or annual herb in the Asteraceae family that grows best in temperate regions. The plants bloom all summer and grow best in full sun with well-drained, organic soil. The marigold is an ornamental, flowering plant of several genuses. The two most popular are the Tagetes (Figure 1A), the true marigold, and the Calendula (Figure 1B), which include the pot and field marigolds. The tagetes has a floral head in red, yellow, orange, gold, and white shades. The heads can be 4-6cm in diameter and are composed of both ray and disk flowers that all appear similar and tuft together uniformly on the terminal meristem. The Tagetes marigolds have green pinnate leaves and produces seeds that have come to most recognized by beginners to gardening (Delger, 2006).

The Calendula marigold produces an inflorescence that better fits that of its native family, the daisy. The Calendula leaves are arranged in whorls and are slightly pubescent.

Figure 1 – (A) Marigold genii Tagetes and (B) Calendula

The flower heads range from yellow to orange and the ray flowers extend from 5-18cm long, leaving the disk flowers congregated in the center, not unlike the common sunflower. While the tagetes marigold has a pungent or musky odor, the Calendula marigold emits a spicy scent, making it more suitable for ornamental uses (Delger, 2006).

The Tagetes genus is most favored by home growers as bedding plants and the two most popular varieties are the African and French marigolds. The African marigold, Tagetes erecta, will have orange to yellow flowers and grow from 25 to 90cm tall. They are so tall, that these marigolds have often been used as background plantings. The French marigold, Tagetes patula, are smaller and bushier. They have a wider range of color, from yellows, to oranges, to mahogany red. Other varieties can have more than one color flower on the same plant. They grow from 15 to 46cm tall and shoots may produce multiple flower heads. The French marigolds have a longer blooming season than the African marigolds. The French are better for both mass planting and small conatiners. They also hold up better in rainy weather than the African marigolds. A crossbreed between these two marigolds exists. The triploid hybrids are called “mule marigolds” because they are sterile and cannot set seed. This means that the plants will bloom continously throught the growing season (Delger, 2006).

There is another variety of marigold worth noting. Signet marigolds (Tagetes tenuifolia) are bushy with fine, lacy foliage. The small, single flowers literally cover the plants in summer. Flower colors range from yellow to orange and the buds are edible. They have a spicy, tarragon flavor. The plant itself gives off a lemony fragrance.


The term “marigold” has two possible lineages. The plants were sometimes associated with the Virgin Mary in older Christian stories. The name could have derived from “Mary’s gold.” The name might also derive from the Saxon word “ymbglidegold,” which translates to “it turns with the sun” (Jauron, 1996).

The marigold originates in Central America. It was discovered by the Portuguese in the 16th century and introduced to South Asia where it became a vital part of ancient culture. The golden color of the flowers became a symbol for the Arya, or honorable people, from royalty to houseguests. Marigold plants were used to decorate pavilions, sacred fire-pits (kunds), and funeral pyres. In India, marigolds became commonplace in weddings and holy ceremonies. Marigold garlands were made as offerings to the Indian gods. When dried, the marigold petals produced a yellow powder used to decorate homes. Perfumes could be made from fragrant oils extracted from the buds. Today, marigolds are cultivated in the tropics and subtropics as well as India and Pakistan. They plants have found use in medicine, dyes, and food flavorings, but continue to serve as popular ornamentals worldwide (Drori, 2005).


To preserve marigold seeds, the whole carpels are harvested in the fall under dry conditions and broken later to remove the seeds. Each pod contains over 150 seeds. The seeds and remaining pods are spread on a metal tray and set aside to cure. They can be heated by a stove set to 140F to dry faster. The point of drying is to removing all water to prevent mold or insect feeding. The seeds can then be stored in a paper bag until the next spring, a safe distance from mice (Heidi, 2008).

Medicinal Uses

Calendula is the marigold that is used more for it’s applications in medicine and pest control. In the early stages of marigold cultivation, apothecaries noticed the plant’s remarkable healing powers. The ancient Romans discovered that this marigold bloomed on the first day of each month, and therefore, named it for the calendar thus, the Latin name, Calendula officinalis. “Officinalis” is the word to indicate official medical abilities as accepted in a pharmacopoeia (Herbal Medicine Guide, 2008).

Henry the VIII used marigolds in his personal recipe, “Medycyne for The Pestilence.” In this he used a handful of marigold, sorrel, burnet, feverfew, and a half-handful of rue, and a few snapdragons. He wrote:

“This tea, if it is taken before the pimples do apere, then ye will hele heal the syke sick person with God’s Grace.”

Lotion made from Calendula officinalis is used to sooth painful lesions on victims of dry eczema. Ointments and baths made from the officinalis can be used to treat chapped skin, bodily scars, and varicose veins. A chest rub solution of marigold steeped in lard, turpentine, and rosin to lower the pulse during intense fevers. A hot tea of officinalis marigold and apple cider vinegar is said to reduce inflammation. Calendula officinalis can be used to treat Leukorrhea, a white vaginal discharge caused by a yeast infection, under the right conditions. A milk lotion brewed with Calendula marigold heads is a natural treatment for knee sprains. Homeopathic surgeons during the Civil War were often forced to create tinctures of the extracted juice of Succus calendula and alcohol to treat wounded soldiers. The herbal, “The Garden’s Labyrinthe” (1577) described the use of marigold as a cure for toothache:

“The juice of Marigold petals mixed with vinegar to be rubbed on gums and teeth becomes a soveraigne remedy for the assuaging of the grevious pain of the teeth.”

Industrial Application

These marigolds are also used as a food additive in many farm products. The color of egg yolks and broiler skin are attributed to the petals from Tagetes erecta as a source of pigment in poultry feed. The petals are ground into a fine meal, containing esters of xanthophylls, also called lutein. The meal is often enriched with a saponified (decomposed to form an acid and alcohol) extract for better absorption, and is added to the feed. Marigolds are grown for this purpose in various locations in the western hemisphere, primarily in Mexico and Peru, by and for various companies who produce feed additives. The marigold flower meal that remains after removal of the xanthophyll esters by extraction was chosen as a potential source of a natural gum used as an edible food stabilizer in the food industry. This meal gum, called gum Arabic or gum acacia, was believed to contain a polysaccharide component that had the ability to protect hydrophobic substances from oxidation (Medina and BeMiller, 1993).

The Whistler Center for Carbohydrate Research in Purdue University has been searching for ways to meet the need for an alternative to gum arabic, the supply of which has been variable and uncertain. Unique properties of gum arabic are its ability to emulsify, or colloidally suspend itself in another liquid, and its ability to form high-solids and low-viscosity solutions. The marigold pigment is extracted by forced pressing to remove water. The resulting cake is dried, rolled into pellets, and extracted with hexane. It is sold to food manufacturers and producers in bulk quantities. The remaining meal is used as a source of marigold flower polysaccharide (MFP) in this work. MFP can be extracted from the meal with warm (50° to 55°C) water. MFP was determined to be a protein-polysaccharide. The crude extract is dark, and a procedure involving an oxidative pretreatment of the meal prior to extraction of the gum was worked out to give preparations of minimal color. MFP has emulsifying and emulsion-stabilizing properties equivalent to those of gum arabic towards limonene and slightly less than those of gum arabic towards olive and castor oils. However, it is not possible to prepare concentrated emulsions with MFP because of the high viscosity of its solutions, at least at concentrations above about 5% (Medina and BeMiller, 1993).

Figure. 2. Preparation of MFP. aHand or machine picked. bProdomex MFP (not ensiled). cKemin Industries MFP (ensiled). dPigment was removed from fresh petal MFP by extraction with methanol and benzene-ethanol, in that order, then hexane (Medina and BeMiller).

Cancer Research

The lutein produced from marigold extracts may also help fight breast cancer. A study conducted by the Program in Nutrition and Department Animal Sciences in Washington State University found that high levels of dietary lutein can inhibit mammary tumor growth in mice. However, the anti-tumor effect of any other levels of lutein were not yet available. In a recent experiment, mice were inoculated with 0 to 1×106 tumor cells in the right inguinal mammary fat pad. A tumor cell load of 2.5 ? 103 cells/inoculation produced approximately 65% tumor incidence. In a supplementary experiment, the optimal number of cells determined from the first experiment was used to test the efficacy of dietary lutein against tumor development. The lutein was introduced into a population of mice’s diet at 0%, 0.002%, 0.02%, 0.2% and 0.4% per meal. After two weeks, the mice were inoculated with the tumor cells and tumor growth was measured daily for a 70 day period. Tumors in the blood, liver, spleen were obtained and observed as well. The scientists discovered that lutein uptake increased dose-dependently. This means that mammary tumor incidence decreased as the lutein concentration increased. In fact, they found that low levels (0.002 and 0.02%) of dietary lutein lowered the tumor incidence more efficiently than higher levels. This experiment may prove useful for marigold treatment in human application (Chew et al., 1998).

Nutrient Issues

Some cultivars of the previously mentioned African marigolds (Tagetes erecta ) are prone to develop a specific physiological disorder of the leaves from iron excess. This disorder is characterized by a speckled pattern of chlorosis and/or necrosis on the leaves as well as a downward curling of the leaves. Some commercially grown marigolds that exhibited the disorder had excessively high concentrations of iron and manganese. In several trade and extension publications, the disorder has been identified as an “iron toxicity” and it appears to spread to other floriculture crops including (but not exclusive to) New Guinea impatiens, Sultana impatiens, cutting geraniums, vinca and some species of Brassica. The disorder, called “Bronze Speckle,” results in economic devaluation of the crop due to extensive aesthetic damage. The occurrence of ‘Bronze Speckle’ as a physiological disorder of marigolds and other bedding plants seems to coincide with the use of soilless media, which are high in chelated micronutrients, particularly iron. Chelates like diethylenetriaminepentaacetic acid (DTPA), or ethylenediaminepentaacetic acid (EDTA) serve to keep the metal in an available form for plant uptake across a wide pH range. However, the fate of chelated metals in soilless media is not as understood. Peats are known to vary widely in the amount of iron which is extractable by chelates. The use of chelated micronutrient fertilizers may lead to surpluses or deficiencies of iron or manganese for plant uptake (Albano et al.)


Botrytis blight or gray mold is a fungus disease that infects a wide array of herbaceous annual and perennial plants, including marigold. There are several species of the fungus Botrytis which can cause blights; the most common is Botrytis cinerea. Botrytis infections are favored by cool, rainy spring and summer weather usually around 15C (60F). Gray mold can be particularly damaging when rainy, drizzly weather continues over several days. The afflicted plant will have masses of silver-gray spores on the dead or dying leaves. The spores may appear as a dust coming off of heavily infected plant material. The best way to manage this disease is by inspection and sanitation. The best treatment is to simply remove faded or blighted flowers, blighted leaves, or entire plants infected at the base, preferably when plants are not wet with dew or rain since this could spread fungal spores. This material may discarded or burned (Snover, 2007).

Oedema occurs when roots take up water faster than it can be used by the plant or transpired through the leaves. Water pressure then builds up in the mesophyll, or internal cells of the leaf, causing them to enlarge and form tiny swollen blister­-like areas. For marigolds, oedema appears as small, sometimes corky blisters which form on the lower surface of leaves or needles (Figure 3A). These blisters may eventually harden to form white, tan, or brown wart­-like corky bumps on the lower leaf surface. In severely affected plants, these corky growths also form on petals (Figure 3B), petioles, and stems. As injury continues, leaves turn yellow, droop, and fall off, or abscise. Oedema can be avoided by monitoring irrigation and not over-watering your marigold crop. In the winter, humidity should stay below 70% (Snover, 2007).

Another common marigold disease is powdery mildew. There are numerous fungi that fall under the general description this affliction. Most have similar habits and similar management/treatment practices. The actual injury to the plant varies greatly with the species and even the variety attacked. Powdery mildew appears as a dusty white to gray coating over leaf surfaces or other plant parts (Figure. 3C). Marigold leaves will often turn yellow or brown, curl inward, and fall off the plant. Newly emerging shoots/leaves will be crinkled and distorted. The fruit will be dwarfed and will abscise early (Jauron 1996). In most cases, this fungal growth can be partially removed by rubbing the leaves. It starts out as discrete, usually circular, powdery, white spots that will coalesce, producing a continuous matt of mildew. Here, fungicides are the favored treatment. There are several effective fungicides available for different sites and plants, but use varies with each product (Snover, 2007).

Figure 3 – Common Marigold Diseases (A) Rose affected by botrytis blight (B) Oedema blisters on spruce needles (C) Powdery mildew on the underside of rose leaf (Snover, 2007).

Pest Control

Marigolds do not usually attract many insects. In fact, marigolds are often used to repel pests from vegetable crops. Slugs and cabbage moths may be found near the plants, but they cause little damage. The pest that would be the most detrimental to the plant is the parasitic nematode (Figure 4). More common in the southern United States, the marigolds as well as many annual ornamentals are at risk if planted in soil heavily infested with nematodes. They may develop serious root problems, grow poorly, and die. There presently are no nematode pesticides, but proper planning can have a substantial effect on the marigold’s performance. There are several other methods of nematode treatment. For example:

-Preparing new planting sites properly

-Replacing infested (contaminated) soil

-Using nematode-free stock

-Selecting marigold hybrids that are well adapted

Figure 4 – Life Cycle of a Plant Parasitic Nematode (Snover)

There are two types of nematodes, those that spend their life underground, feeding on soil and roots, and those that spaend at least part of their life feeding on plant foliage. The most common of the latter is the root knot nematode (Meloidogyne sp.). Root knot nematodes are known to infest over 200 reported plants, including the marigold (Figure 5B). Other commonly found root feeding nematodes include Stunt nematode, (Tylenchorhynchus sp.), Lance nematode (Hoplolaimus sp.), Spiral nematode (Helicotylenchus sp.), Lesion nematode (Pratylenchus sp.), Cyst nematode (Heterodera sp.), and Ring nematode (Criconema sp.).Most foliage-feeding nematodes belong to the genera Aphelenchus or Aphelenchoides. Symptoms for either nematode may vary based on the plant parts attacked or species of nematode present (Snover, 2007).

Nematodes that feed on the roots cause above ground symptoms that are similar to those resulting from many kinds of root injury. Foliage loses its luster and prolonged root stress may result in yellowing and eventual leaf abscission. Any new growth is stunted and weak, with fewer and smaller leaves than healthy plants. Plants tend to wilt more readily during drought conditions than uninfected plants. The damage is usually distributed irregularly, since nematodes are rarely distributed evenly in the soil. Nematodes that feed on the foliage produce angled lesions on broad leaved plants (Figure 5A) (Snover, 2007).

Root symptoms, however, have a wide variability. Some kinds of nematodes cause tissues on which they feed to grow strangely. For example, the plant may develop root-knot, stop the growth of the roots or kill the cells on which they feed as they move through the roots. Other symptoms may include galls, stunting, root decay, and root discoloration. Nematodes are also known to transmit viruses. Laboratory soil sample Figure 5 – (A) Characteristic angled foliar lesions and (B) Root knot (Snover). Analysis or foliar analysis is the only way to detect the kinds of nematodes associated with an infected plant, which may be necessary to identify the most effective control measures.


Over a 14-week period, a greenhouse crop of marigolds were cultivated. Seedlings were started in January 23, 2008 from standard Pro-mix ™ plugs. After transplanting into 4” pots, the first height measurements were taken on February 11, 2008 and the last were taken on March 31 (Figure 6). The Greenhouse temperature was maintained at a constant 72?C during the day and 68?C at night. Nitrogen fertilizer was applied at 150ppm at regular watering intervals. EC and pH for each pot were recorded every week and the combined EC and pH for every treatment was recoded on February 18, March 3, and March 31, 2008 (data not available).

For the best results, it is recommended that the marigold crop be seeded directly. The seeds are disposable and plentiful enough to disperse freely or sow with automatic seeders. Since the seeds do not need light, vermiculite or other cheap, water-retentive mulch can cover the crop. The greenhouse should be kept at a constant 64-72F during the day. At night, the greenhouse temperature should be 60-65F. The media pH should be 6.0 to 6.2 and the EC should be less than 0.75mmhos/cm. After the seedling emerges, the temperature should be reduced to 68-70F. The crop should be fertilized with 50-75ppm nitrogen as soon as the cotyledons unfold. Marigolds are short-day plants, so the critical photoperiod is 12.5 to 13 hours. Light intensity should remain high and the best growing medium is Peat-lite™, a light, well-drained soil mix with a pH of 5.8 to 6.2 and an EC less than one mmhos/cm. After the shoots have developed, the fertilizer should be changed to a 15-15-15 (nitrogen/carbon/potassium) fertilizer. It should be applied at 100-150ppm N. The optimal nutrient content in marigold foliage is listed in Table 1 (Kessler Jr., 2008).

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