CALENDULA - An Herb Society of America Guide

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DESCRIPTION AND CHEMISTRY OF CALENDULA 

Botanical Dr. Arthur Tucker

Calendula officinalis L., Sp. pl. 921. 1752. Native country: Poet’s marigold is native from Europe to Iran and North Africa. General habit: Poet’s marigold is an annual to perennial, woody only at the base, with stems 20 to 50 cm high. Leaves: Leaves are 7 to 14 x 1 to 4 cm, lance-shaped with narrowed bases, narrowly parallel-sided, or spoon-shaped, shortly tapering to the apex or blunt, glandular-hairy to sparsely spidery-cottony hairy, usually with a smooth edge to obscurely wavy-toothed. Flowers: Flowers are 4 to 7 cm in diameter, yellow or orange. Fruits/Seeds: Outer fruits (achenes) are incurved (or rarely flat) narrowly beaked, 2 to 2.5 cm, alternating with shorter boat-shaped (rarely 3-winged) achenes. 

The genus Calendula includes about twenty species of the Mediterranean, but only C. officinalis has been used in medicine or the kitchen. Large yellow to deep orange daisies, sometimes tipped in red and up to 3 inches across, are borne from tufted, light green, lance-shaped foliage, making this a very attractive annual for the border. The petals of poet’s marigold also yield a dye for fabric or hair. Wide-ranging medicinal claims have been made for poet’s marigold petals, but little research has tested these assertions. The petals have been found to be anti-inflammatory and promote wound-healing and may aid in the treatment of acute dermatitis, however, due to the content of isorhamnetin and faradiol monoester. The faradiol esters also provide anti-oedmatous activity. In addition, the high concentration of carotenoids, which are antioxidant, is well-documented and provide scavenging activity against free radicals. The flower extract may be both genotoxic and anti-genotoxic. Flowers also exhibit both spasmolytic and spasmogenic constituents and may be useful in abdominal cramps and constipation. The flowers of C. officinalis contain 0.009 percent pyrethrins, so an extract would be also effective as an insecticide.

Some single and many double forms (‘Bon Bon,’ ‘Gitana,’ ‘Prince,’ and ‘Touch of Red’ series) are currently cultivated. One quaint form, ‘Prolifera,’ is the henand-chickens poet’s marigold because of the “proliferated head,’’ which radiates smaller heads out from it in the manner of hen-and-chickens (houseleek), Sempervivum tectorum L. Gerarde called this form “Jack-a-napes on horsebacke.’’ An investigation of 10 cultivars of C. officinalis in Italy showed that ‘Calypso Orange Florensis’ produced the highest amounts of bioactive monoesters, followed by ‘Fiesta Gitana Gelb’ and ‘May Orange Florensis.’ Another study done in Austria with eight cultivars in two different locations found that the diameter of the flower heads, dry weight of the inflorescences, and content of faradiol-3-monoesters proved to be stable parameters, regardless of the environment. A study by the same authors found that the inheritance of the faradiol monoesters was complex and polygenic and not correlated with flower size.

Important Chemistry: The essential oil of poet’s marigold flowers is dominated by 2-64 percent alpha-cadinol and 8 to 10 percent eudesmol along with many fatty acid esters and sesquiterpenes, providing a pleasant, spicy odor. The bitter principle is (-)-loliolide (calendin). The carotenoids, which provide the distinct yellow to orange of the petals, are beta-carotene, lycopene, violaxanthin, and lutein; in addition, flavonoids, narcissin and glycosides of quercetin and isorhamnetin, also provide some color. At least eight faradiol and calenduladiol monoesters are bioactive.  



THE MEDICINAL POINT OF VIEW

An Herb A Day: Pot Marigold —– Can Calendula Check Cancer?

Dr. Jim Duke

Calendula officinalis is the herb of the year this year, and a lot of people are talking about it. And maybe it deserves talking about; those golden flowers seems to be one of the richest sources of carotenoids, even the famous lycopine and lutein. If so, this belongs in the food farmacy as a possible, even probable, cancer preventive food. Facciola (3) notes that the fresh flowers are chopped into salads, dried petals used like saffron, to color butters and cheeses in teas, and to flavor cakes, cookies, puddings, and soups. 

From my updated database, we read that the flower heads are used in cookery; they were used as a soup starter in the Middle Ages; dried flowers are used to make broth and to color cheese; pickled buds have been used as poor caper substitute; leaves can be cooked and eaten like spinach. My Living Liqueurs, printed twenty years ago, has been out of print so long that I had all but forgotten I had a pot marigold account there. And there’s still stuff in that 1987 book I haven’t seen resurface elsewhere, so for a change I’ll quote Duke and Duke (2): “Fresh, dried or frozen petals may be used in any recipe as a saffron substitute... Marigold powder...is used like saffron to season seafood, chowders, soups, stews, roast meats, and chickens. It is also used to color butter, cheese, custard and liqueurs. I have used both Calendula and Tagetes to simulate the color of Galliano (2).”

I had not planned to write up this herb, until the FDA came flip-flopping along and said there was no conclusive evidence that lycopene could prevent cancer. But they did leave us with one little glimmer of hope; “The FDA found very limited evidence to support an association between tomato consumption and reduced risks of prostate, ovarian, gastric, and pancreatic cancers.” X17623802(4). Since calendula can contain as much lycopene as tomatoes, I’m assuming that calendula can help prevent these cancers too, though I am rather sure the FDA would not agree.

The FDA proudly used the aphorism “evidence-based” in their lycopene/tomato study title saying there was no evidence for lycopene and only limited evidence for tomato in cancer prevention. I have a strange line of evidence I call the Multiple Activities Menu (MAM) which lists many activities that might contribute to the prevention, alleviation or curing of cancer. I present that MAM first. It’s rather impressive, the list of phytochemicals in calendula that might prevent cancer. These reports are based on phytochemicals in the USDA phytochemical database (1). I might add that the phytochemicals and their activities were reported by someone else, not the FDA, not me. Sources can be found in that USDA database.
But moderation in all things. Two studies show that relatively low doses may be beneficial in several directions but higher doses detrimental. Remember the dose makes the poison. Reasonable intake of calendula, like probably all herbs, can be beneficial, massive doses harmful. Reasonable doses can provide several useful carotenoids, not just common chemopreventive carotenoids like lutein and lycopene, but a few that are unique to calendula. All herbs contain many common phytochemicals, shared with all plant species, and probably all herbal species contain some phytochemicals not shared with other species.



Medicinal Use of Calendula Gayle Engels

Calendula (Calendula officinalis) has a long history of medicinal use extending back to the ancient Egyptians (8). Also called marigold, pot marigold or poet’s marigold, calendula should not be confused with Tagetes spp. The plant material used medicinally is the whole or cut, dried, fully opened flowers, with the petals having been detached from the receptacle (6,14).

The herbalists Gerard and Culpepper both mention marigold and Maud Grieve states that it is primarily a local remedy and that applying the petals to insect stings will reduce the pain and swelling (10). She also recommends a lotion made of the flowers for sprains and wounds and a water distillation of the flowers for sore and inflamed eyes. While the flowers are the part most often used medicinally, Mrs. Grieve also claims that the juice from the leaves will remove warts and that eating the raw leaves in salad was useful in the treatment of childhood scrofula, a tubercular degeneration of the lymph glands (10). European folk healers utilized extracts, infusions (teas) and ointments made from the calendula flower to cure jaundice, promote sweat during fevers, and to induce menstruation (1). In the 19th century, American Eclectic physicians used calendula flowers to treat conjunctivitis (an inflammation of the mucous membrane that lines the eyelids, commonly called pink eye), liver problems, stomach ulcers, and superficial burns, sores and wounds (1).

Calendula is both astringent and anti-inflammatory and calendula infusions, ointments and tinctures have been employed to heal bruises, burns, cuts, and the minor infections that they cause (7,13). Calendula preparations have been used to treat skin and mucous membrane inflammation such as pharyngitis (inflammation of the throat), dermatitis, boils and leg ulcers (14). Lotions, poultices, and compresses made with calendula flowers may also be used, based on which preparation is most suitable (11). 

Modern-day herbalists recommend the use of calendula internally for its antiinflammatory effects in the digestive system, that is, for gastric or duodenal ulcers and the many complaints that are commonly referred to as indigestion (11). It has also been used to help with gallbladder problems, and as a normalizer of the menstrual process, may help with delayed or painful periods (11).

The German Commission E approved the internal and topical use of calendula flower for inflammation of the oral and pharyngeal (throat) mucosa. It was also approved externally for poorly healing wounds and foot ulcers (2). Canada has approved calendula as an active ingredient in over-the-counter traditional herbal medicines and homeopathic medicines (14). In the United Kingdom, it is approved as an herbal medicine for external use only in the General Sale List. Calendula is approved in the United States for use in cosmetics, dietary supplements, homeopathic remedies and is generally recognized as safe for food use (GRAS § 182.10) (14).

Calendula’s healing properties, while proven over centuries of use, are not well understood. Various activities have been shown for the essential oil and extracts of the flowers including the following: anti-microbial, anti-inflammatory, anti-bacterial, anti-fungal, anti-tumor, cytotoxic, anti-HIV and wound healing (1,14). Recent studies investigating the calendic acid content of the calendula seed have found it to have antioxidant properties (15).

While there are not many clinical studies to support the various uses of calendula, a few stand out. One 1994 study found that an ointment made with calendula flowers has been effective in relieving the pain associated with cracked or tender nipples (12). In 2005, Duran et al. obtained positive preliminary results for the use of calendula ointment in the treatment of venous leg ulcers (5). Another 2005 study showed the protective effect of a calendula/rosemary cream preparation against a sodium laurel sulfate-induced irritant contact dermatitis (9). A 1999 study suggested that a Romanian product containing calendula, Actium lappa, and Geranium robertianum was more successful at resolving complaints and healing ulceration caused by herpetic keratitis (inflammation of the cornea and conjunctiva caused by herpes virus type I) than was acyclovir alone (4). 

There are very few safety concerns regarding calendula. However, internal use of calendula preparations should be avoided during early pregnancy due to its ability to stimulate menstrual activity (3). Also, allergic hypersensitivity may be an issue for persons sensitive to other members of the Asteraceae family (3).



CULTIVARS OF CALENDULA

Deni Bown

Marigolds self sow in my garden in southeastern England, so I am never without them from about March through to November. It is not easy to find seed of the true pot marigold, so like most gardeners, I usually grow cultivars on the basis that they have showier flowers and yet can be used in the same ways. As cultivars do not come true from seed – and if left to self sow over generations may revert to the wild species – I always sow a named variety to give a more uniform ornamental effect. Every year I use marigolds as an edging or design feature in the vegetable potage, often around zucchini plants that tend to leave the edges of their allotted bed looking rather bare.  

For this purpose I choose a dwarf, compact strain, such as ‘Fiesta Gitana,’ which reaches only 12 inches tall. At the other extreme, I grow tall, longstemmed cultivars which double as cut flowers. Cutting the flowers prolongs the flowering period in just the same way as dead-heading, but with extra enjoyment along the way. ‘Indian Prince’ has striking burnt orange blooms held high on stems over 24 inches long. Another stunner is ‘Greenheart Orange’ with lime green centers. ‘Orange Porcupine’ is shorter, at 15 to 18 inches, but the flowers are quilled and a particular vivid orange. It’s a favorite of mine and comes surprisingly true if left to self sow. For a softer effect there are mixes, such as ‘Art Shades,’ ‘Allsorts,’ or ‘Kablouna Mixed.’ The more muted apricot, lemon, and cream shades, or contrasting mahogany flushed flowers are a good foil for the dominant bright oranges.  
Some cultivars have been around a long time. ‘Prolifera,’ known as the hen-andchickens marigold, is illustrated in a Victorian encyclopedia published in 1885. The main flower produces smaller flower heads from its base, like satellites orbiting a planet. It is not a tidy plant but looks good among assorted annuals and wild flowers – and it’s always good to honor the historical while welcoming the new.

Calendula officinalis ‘Greenheart Orange’ 
Height: 24 inches Description: Rich orange, serrated petals form a floral “ruff” around a limegreen heart. Easy to grow, producing lots of flowers for the garden and making a lovely cut flower for indoors. 

C. o. ‘Kablouna Mixed’ 
Height: 20 inches Description: A cottage garden delight! Large, striking crested blooms of gold, orange, lemon and apricot with a dark contrasting center. Enjoy them in the garden or use them as beautiful cut flowers.

C. o. ‘Nana Apricots & Oranges’ 
Height: 10 inches Description: A striking combination of extra double apricot and orange flowers, borne on dwarf, compact, basal branching, bushy plants. For organic gardeners this makes an ideal companion plant. Flower petals and leaves can be used in salads to add a tangy flavor.

C. o. ‘Nana Citrus Cocktail’
Height: 8 inches Description: An attractive ‘Citrus Cocktail’ of alluring orange and golden yellow. This mouth-watering color combination smothers the extremely dwarf, compact bushy plants, in stunning daisy flower heads. Unlike other calendulas, ‘Citrus Cocktail’ keeps on flowering throughout the summer. Be sure to add a touch of the tropics to your borders or containers!

C. o. ‘Pink Surprise’
Height: 18-24 inches Description: Amongst fiery orange and yellow flowers appears a surprise – delicately ruffled, soft orange blooms with a delightful and unique tinge of pink. Wonderfully easy to grow in the border or containers and a delightful cut flower too.
  
C. o. ‘Porcupine’ 
Height: 18 inches Description: An exciting new English marigold with vivid orange, pointed blooms with an attractive quilling that gives a wild, spiky effect. Wonderfully easy to grow in the border or as bedding. The distinct blooms also make a stunning cut flower.

C. o. ‘Radio Extra Selected’ 
Height: 18-20 inches Description: Glowing orange, beautifully quilled cactus-dahlia-shaped blooms magnificent for cutting and border, flowering well even in the poorest conditions. 

C. o. ‘Sherbet Fizz’ 
Height: 6-18 inches Description: New in 2007. Sherbet Fizz is an easy to grow annual, specially selected for its striking color combination. These unusual buff-colored blooms also have an intriguing darker red underside on several layers of tightly-packed petals, each tipped with red, creating a spectacular sherbet fizz effect as the blooms open. Sown in drifts directly into borders they will make a stunning addition to your garden, as well as making an attractive cut flower.

C. o. ‘Touch of Red’ 
Height: 16-18 inches Description: One of the most outstanding, uniform cut flowers. Blooms have a “touch of red” giving them an almost antique look. 

CULTIVATION
Tips on growing Dr. Arthur Tucker

Calendula plants are easily started indoors four to six weeks before the last expected frost. The seeds, shaped like stiff and twisted vipers, may be directly sown in friable garden loam in full sun about 9 to 12 inches apart. Flowers are generally produced from May until frost if summers are cool. Seeds ripen August-September, and poet’s marigold often reseeds itself in the garden. 

Heat is inimical to poet’s marigold, and southern gardeners will find that their plants cease flowering and suffer from spider mites and black aphids from July to August; partial shade and moist soil will sometimes counterbalance the summer’s heat. Researchers in Egypt found that pre-sowing seeds at a low temperature of 41°F (5°C) for 7 days caused the most pronounced increase in the essential oil.

Flower production is particularly increased by fertilizers high in phosphorus, so fertilizers with an N-P-K ratio of 1-2-1 are recommended. A study done in Egypt also found that an application of urea at the rate of 106 pounds per acre (119 kg/hectare) gave the highest flower numbers and weight. Researchers in New Zealand found that the total flower yield was not significantly different at populations over 46 plants/m2.

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NOTES ON GROWING CALENDULA FROM HSA MEMBERS

Jim Long, Long Creek Herbs, Blue Eye, Missouri 

Calendula grows cautiously in my Zone 6b/7a region and I grow it as a brief, temporary plant. Since it is a cool season plant, and our cool season usually ends by mid June in the Ozarks, I see calendula as a very short season herb. I feel fortunate if I am able to coax three weeks of blossoming from calendulas.

Some of the older German cultivars have a better chance of good flower production, but most cultivars fall prey to little green worms that eat the centers out of the buds before they open. To prevent them, I spray with bacillus thuringiensis every ten days. The plants also have a tendency to turn yellow and die without warning, from the root to the top, leaving empty spaces in the calendula bed. In addition, calendula is a magnet for blister beetles and they will first attack the calendula, multiply, then move on to the tomato plants. 

Carolee Snyder, Carolee’s Herb Farm, LLC, Hartford City, Indiana  I seed calendula early in the greenhouse, especially the dwarf ‘Bon Bon’ series, so I can have them already in bloom when we make up big baskets and pots of cooking herbs. Their lighter green leaves also look good in contrast to the darker parsley, etc. and often people aren't aware they can use them in the kitchen. I also love them because they continue to bloom in the Cook’s Garden even after the first light frosts. The only drawback is that they really, really look pitiful in the hottest days of July and August. I cut them back, and they reward me with lots of autumn blooms. 

Cathy Manus-Gray, Herban Gardens, Cuyahoga Falls, Ohio Calendula thrives in my garden despite my sometimes neglectful gardening practices.  I've had it come up faithfully every year for several seasons now. The varieties I grow are ‘Flashback’ which I obtained from HSA's seed exchange program, ‘Erfurter Orangefarbigen’ which is a commercial strain available from Richter’s that is used for the superior medicinal flower action.

I have calendula in my culinary garden because I use it in salads and in my herbal floral cream cheese. It does very well in this area, which is in full sun and has rather dry soil except when we have a downpour. Then the area becomes pretty saturated and the calendula’s feet are sitting in some water. 

It easily re-seeds itself every year and blooms around mid-July. It will continue to bloom through September until a heavy frost which can come anytime in October. I do deadhead or harvest pretty heavily to encourage re-blooming, but always leave some flowers so they will germinate for next year.  

I start seed indoors and transplant seedlings in the garden. This gives me a jump start and assures I’ll have blooms earlier in the summer.

Theresa Mieseler, Shady Acres Herb Farm, Chaska, Minnesota The last frost in my area is usually around May 25, and it is then that seedlings are planted into the gardens. Flowering begins in late June, and in early September few flowers are left on the straggly plants. At this time many plants have gone to seed and it is easy to spot new plants coming up underneath old stems. Volunteers usually begin sprouting early the next season. 

Plants generally reach a height of 2 to 2 1/2 feet but ultimate size depends on sun and moisture. In 2007 we had a drought, and I noticed the plants had mildew and did not grow as well as other years. I prefer the variety C. o. ‘Erfurter Orangefarbigen’ because it does better in this climate. 

Karen Lee Hegre, Black Hills Herbs & Aromatherapy, Rapid City, South Dakota In western South Dakota, (Zone 4/5), calendula has been re-seeding itself for the past 4 years.  I use a lot of calendula in salves and lotions. I also plant new seeds each spring after the soil warms up in April and May. Without the spring snows the seeds germinate in approximately 14 days, but if we have a spring snow it takes longer. I plant seeds no deeper than 1/4 inch and do not thin them. I have a couple large areas planted with calendula only.  

Geri Laufer, Atlanta, Georgia Atlanta is Zone 7B, lately approaching Zone 8. Calendula is a cool-season in Atlanta. It is planted in mid-October with pansies and blooms all fall, including December and even January. It dies back in cold weather during January to mid-February and then blooms in late-February until the hot weather begins. 

South Texas
Large bright-yellow to orange blooms from fall through spring make calendula one of the most popular cool-weather herbs in South Texas gardens. Once widely used as a potherb, it is seldom eaten anymore, although it is certainly edible. The young leaves are best for cooking, as the older ones turn bitter. The dried petals lend a bright color to potpourri and are used in cooking to add saffron's color, although they lack the saffron flavor.

Pot marigolds are easily grown from seed started in late August and most nurseries in South Texas sell them as bedding plants in the fall. They grow 1 to 2 feet tall (depending on the variety) in full sun and average, fertile garden soil with some humus added. Plant 10 to 12 inches apart and water them well before a freeze or anytime there is a period of dry weather during the winter. They are hardy through most of our winters, although occasionally the buds will freeze if not protected. Keep the plants deadheaded for more bloom. They are usually past their prime by May and may be removed to make room for summer annuals. The Herb Society of America, South Texas Unit, Herbal Harvest Collection Cookbook

Karen Mahshi, Concord, CA Calendula blooms in our area from late fall through spring. The foliage begins to turn brown by late May and the plants shrivel up with the onset of hot weather. If I am going to harvest flowers for drying (potpourri) I try to do it no later than mid-spring. The flowers decrease in size as the weather warms.

COMMERCIAL CULTIVATION
Calendula Conrad Richter

Calendula’s main commercial value lies in the flowers used in medicinal and cosmetic preparations. To a lesser extent, calendula is also grown for its edible fresh and dried flowers to add color to foods. Farmers feed the flowers to laying hens to deepen the colour of the egg yolk. The potential of the seed oil for industrial applications has been explored and development of the crop for this purpose is close to commercialization.

Cultivars
Of the more than 100 cultivars of calendula known to exist, most are intended for the ornamental market. Historically, North American growers have chosen to grow ornamental cultivars assumed to be bioactive. The Czech variety, ‘Plamen,’ registered in 1941 and still cultivated as a medicinal crop in Europe, is said to be a progenitor of many early ornamental cultivars such as the Pacific Beauty series. Neither ‘Plamen’ nor its improved large-flowered version, ‘Plamen Plus,’ are available in North America. 

In Europe and North America the standard variety for commercial production is ‘Erfurter Orangefarbige,’ a high-yielding, large, double-flowered type with high flavonoid and carotenoid content. Dry flower yields of 1500 lbs/acre (1.7 tonnes/hectare) have been recorded for this variety. Compared to ‘Erfurter Orangefarbige,’ yields of ‘Resina,’ an American variety with mostly yellow flowers, are similar, but flavonoid content is as much as a third lower. 

Both ‘Erfurter Orangefarbige’ and ‘Resina’ were evaluated for oilseed production but seed yields of 0.6-0.8 tonne/hectare are too low compared to the 1.35 tons/acre (3 tonnes/hectare) of some European selections. A proprietary European variety, ‘Carola,’ registered in 2005, is apparently the first to come out of European oilseed research; but it is not available in North America. ‘Regina,’ an older European oil-rich variety is also not available to North American growers. For competitive reasons the use of proprietary selections appears to be common in the industry. 

For example, the German herbal medicine manufacturer, Dr. Theiss, registered ‘Rinathei’ in 1998 for its own exclusive production use. This variety is claime to be rich in faradiol triterpenoids believed to be most responsible for calendula’s anti-inflammatory activity. Intriguingly, a readily available dwarf ornamental variety, ‘Calypso Orange,’ is also rich in faradiols, having the highest content of 10 cultivars tested, as much as a third more than ‘Erfurter Orangefarbige.’

Site Selection and Preparation
Cool temperate areas with mild summers are best suited for calendula. Where summers are too hot, yields are depressed. Typical USDA zones where calendula is grown successfully are Zones 2 to 9. Calendula prefers full sun, and will tolerate a range of soils if the drainage is good. It does not require a bare fallow period prior to planting. The ground should be finely worked to provide a smooth surface for sowing. Calendula is a hardy annual. Planting occurs in early spring or, where winters are mild, in the fall. 

Direct Seeding
For rows 28 inches (70 cm) apart with a final plant density of 5  to 7/10ft² (5  to 7/m²), the traditionally recommended seeding rate is 2 to 2.5 lb/acre (2 to 3 kg/hectare). One study suggests that dry flower yields can be tripled with broadcast sowing at 20 lb/acre (24 kg/hectare); but the decision to sow in rows or broadcast depends on weed control, harvest method and seed cost. Broadcast sowing is only feasible if herbicide use is planned. For oilseed production broadcast sowing is preferred. For oilseed production the seeding rate of 24 kg/hectare is recommended; this will result in plant density of about 60/m². 

Indirect Seeding and Transplanting
Sow in plugs or seed beds 4 to 6 weeks prior to field planting. At the seed density of 3700 seeds/ounce (130 seeds/g) approximately 2.20 pound of seed (1 kg) of seed is needed to plant 1 lb/acre (1 hectare). Plug trays with 128 cells planted 2 seeds per cell works well. Seeds need light to germinate so they should be covered very lightly or just pressed in. Transplant seedlings to the field in rows spaced 70 cm (28 inches) apart with plants spaced 6 to 8 inches (15 to 20 cm) apart within rows. 

Fertilizer and Growth Control
Too much nitrogen reduces flower yields in favor of unmarketable foliage. If nitrogen is very low, up to 45 lbs/acre (50 kg/hectare) may be applied. Phosphate (P2O5) and potassium (K2O) may be applied at the rate of 90 lbs/acre (100 kg/hectare) and 45 to 90 lbs/acre (50 to 100 kg/hectare), respectively. Organic growers may apply compost or composted manure at 10 tons/acre (20 tonnes/hectare) if soil fertility is low. The microelements Boron, Molybdenum, Zinc, Manganese, and Cobalt are known to stimulate flower production and carotenoid content. Maleic hydrazide (50 mg/litre) induces branching and flower formation.

Irrigation
During dry periods calendula needs 1 to 1.5 inch (2.5 to 4 cm) water per week. 

Weed Control
If planted in rows, regular cultivation and hoeing is usually sufficient to keep weeds down to levels that do not interfere with flower production or harvest. A plastic weed barrier works for transplanted fields but may not be cost effective. Effective chemical controls include the preplant herbicide ethalfluralin (Edge) and trifluralin (Bonanza), the pre- or postemergent herbicide propyzamide (Kerb), and the postemergent herbicide sethoxydim (Poast Ultra). 

Diseases and Pests
The main problems are powdery mildew (Sphaerotheca fuliginea and Erysiphe cichoracearum) which damages flowers during cool periods, and aster yellows, which causes stunting and deformation of flowers. For mildew, preventative applications of sulfur or baking soda sprays may help. Mild infections can be treated with neem oil or horticultural oil sprays. Picking flowers early and often avoids late cool season mildew. Aster yellows infection rates as high as 27% have been reported. There is no treatment other than to remove infected plants. It is spread by aster (six-spotted) leafhopper so prevention centres on controlling leafhopper. Control measures include monitoring leafhopper with sweep nets and treatment with neem oil, soap and pyrethrum sprays or with chemicals such as endusulfan (Thiodan, Phaser) and carbaryl (Sevin). Blister beetles, cabbage loopers, and caterpillars are the other main pests. 

Harvesting
Flower heads can be harvested by hand-picking or by using a comb. Hand-picking results in a superior product as the comb method will capture buds, over mature flowers, and seed heads. The combed product either has to be picked over to remove the unwanted material or must be sold at a lower price. Fresh flower yields range 2.5 to 4 tons/acre (6 to 9 tonnes/hectare). A worker can hand-pick 25 to 45 lbs (12 to 20 kg) of fresh flower heads per hour. Harvesting labor can account for up to 80% of the total production labor required to produce the flower crop. For oilseed production the crop is dessicated with diquat (Reglone Dessicant) and then combined.

Drying
Calendula flower heads require shade, ventilation and artificial heat to dry. Because there are numerous sites on the flower heads where moisture can accumulate, drying must be done carefully. The flower heads should be spread on screens no more than one layer thick. A brief period of elevated heat at 50 to 120 to 140ºF (60ºC) to remove surface moisture is followed by a sustained drying period of not more than 95ºF (35ºC). If required product is to be petals only, then the petals can be rubbed off when the petals are dry and the centres are not yet hard. When centres are hard and no longer pliable flower heads are ready for processing or storage. 

Processing
Depending on the intended market the product may or may not need further processing such as cleaning. For whole flower heads no further processing is usually required. For a petals only product winnowing may be required to clean the product.  

HARVESTING, PRESERVING AND STORING CALENDULA

Home gardeners may harvest flowers by cutting the heads from the stems and drying them in the shade on paper; the petals will stick to screens, overlapping of the petals results in discoloration. Store the dried petals in tight, opaque containers to prevent fading and discoloration. – Dr. Arthur Tucker

You can use silica gel or kitty litter to dry calendula flowers to retain color and shape. Use a cardboard box approximately 12" x 16" making sure the ends are secured with duct tape so the mixture doesn’t leak out (any size box will do even a shoe box). Cut the flowers leaving 1" of stem. Sprinkle the silica gel or kitty litter to cover the 1/2" of the bottom of the box  and gently lay the flowers face down on the kitty litter or silica gel. Place flowers about 1/2" apart and cover the flowers with the silica gel or kitty litter until you don’t see any of the petals and allow it to sit undisturbed for five to seven days in a dry area.

When dry gently lift them out of the mixture and brush off excess material with a soft paint brush. Spray with hairspray to keep the shape and to keep the flowers from wilting. At this point the dried calendula can be used in arrangements or wreaths. – Theresa Mieseler

PROCESSING CALENDULA

Rexford Talbert Super-critical CO2 extraction is another plant essence extraction method in addition to the usual steam distillation process. This technique has the advantage of not distorting or destroying some of the volatile oil components as much as other extraction procedures. This approach also allows a more efficient separation of waxes and other more solid lipids from the extracted mixture.

Calendula is relatively fragile as compared to mint, thyme or lavender leaves and inflorescences and must be extracted by enfleurage, a direct adsorption of the essence, or by carbon dioxide (CO2) that has been heated until it changes to its liquid state. This super-critical CO2 directly allows the ethereal oils to be absorbed.

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