Scientific Name: Calendula officinalis
Family: Composite
Brief history and botanical notes on the plant
Marigold is an annual plant present spontaneously throughout the Mediterranean basin, it can be found in uncultivated meadows, on roadsides and can reach 600 meters above sea level if the exposure is favourable. It has been exported to northern Europe, Asia and also to the American continent mainly as an ornamental plant rather than for its truly important medicinal virtues. All types of marigold are believed to be derived from a single species, C. arvensis.
In its spontaneous state it can even reach 80 cm in height, while in cultivation it does not exceed 30-60 cm.
It is a polymorphic species, often very branched with striated and robust stems, generally characterized by thick hair. The root is of the taproot type, although not very deep (about 20 cm). The leaves are alternate and sessile, rounded or acute, generally pubescent. The lower ones are stockier and arranged in a rosette while the upper ones are more lanceolate.
The flowers (flower heads 3-7 cm in diameter) have a color ranging from orange to pale yellow to almost white and are collected in the period from June to November. Each plant can produce up to over 60 per year if well nourished. The fruits are curved, squat and spiny achenes, with at least three prevalent types: winged, sickle-shaped and ring-shaped. Depending on the variety, the weight of 1000 seeds can vary between 8 and 15 g.
Family and variety
The Calendula genus belongs to the Asteraceae family, includes around thirty species and among these we highlight:
Calendula officinalis: it is the best known and most widespread species. The flowers have a color ranging from yellow to orange to white. There are numerous ornamental and medicinal varieties which differ in the different sizes of the flowers, their colour, the size (dwarf varieties) and the length of the flower stem (cut flower varieties). Among those most suitable for medicinal use are Erfurter Orangefarbige (single and double), Kablauna Orange and Gitana Orange.
Calendula arvensis: it is the species that we find spontaneously in our meadows. The flowers are yellow or orange, the leaves are alternate and covered with dense hair. It flowers from June to November.
Pedoclimatic needs
Marigold adapts to different environments and soils thanks to its rusticity, with good exposure it can also be grown on hills up to 600 m above sea level. The optimum vegetation is between 20-30 °C.
It prefers soils rich in organic substance and well-aerated and drained substrates, as it fears stagnation, but must never be subjected to water stress.
It is preferable not to repeat the cultivation on the same soil for at least 4-5 years.
Sowing and transplanting times
Since Calendula officinalis L. resists temperatures down to -2 °C, it is possible to sow in autumn in order to bring flowering earlier and obtain larger flower heads and higher yields.
In northern Italy, spring sowing is carried out starting from the month of April with a planting spacing of around 5-8 plants per square meter and with a row spacing of 45 or 75 cm depending on the seeder and the machines available (seeders for vegetables are fine). The quantity of seed to be used is between 2 and 4 kg/ha depending on the variety. In crops set up for ornamental purposes, transplanting can be carried out in April-May after having produced the seedlings in the seedbed.
The duration of the biological cycle of marigold is approximately 80-120 days from the moment of sowing. Complete germination occurs in two weeks, after 25 days the flower buds form, after another 30-50 days complete flowering (which can last for 20-30 days or more) and, finally, maturation of the seed after another 15 days. Due to the scalar flowering, mature seeds and flower buds are found on the same plant. Sowing can be carried out in seedbeds from the end of February to April, while transplanting can be carried out between May and mid-June when the seedlings have reached a height of 12-15 cm (pruning leaves and roots), maintaining a distance of approximately 35 cm between rows and 20 cm on the row.
Fertilizations
Marigold is a demanding species regarding phosphorus and potassium which have positive effects on the yield of flower heads. The nitrogen supply must however be modest as it depresses the production of flowers and favors the development of the leaves. Since the plant takes advantage of the presence of organic substance, if available, manure can also be added to the soil (30-40 t/ha).
Crop care and irrigation
It does not require particular cultivation care, weed containment can be carried out during cultivation with mechanical weeding in the inter-row starting after emergence and possibly manual weeding on the row. In some cases, especially for ornamental plants, it is possible to resort to mulching with plastic materials or plant residues, but the cultivation cost tends to increase significantly.
As regards irrigation during the transplanting phase and before harvesting (if necessary), these are fundamental, while during the vegetative cycle they will be influenced by the climatic trend, it is possible to carry out a few but important waterings which in total are around 5 in total.
Adversity
Among the most important pathologies we can mention: Sphaerotheca fuliginea (powdery mildew of marigold), which mainly affects the foliar system causing yellowing and drying of the green parts; Entyloma calendulae, which mainly attacks the branches and manifests itself first with yellow-green and then brown spots; Erysiphae cichoracearum and Alternaria calendulae, which damage the foliar system; Cercospora calendulae, which causes failure to grow and deteriorate the plant and also forms circular gray spots.
As for insects, seedlings can be attacked by wireworms (Agrostis sp.) and adult plants by tobacco noctule (Noctua pronuba L.), aphids and whiteflies. Copper and sulfur can contain these adversities.
Production and collection
The collection of flowers is carried out manually by carrying out multiple passes in the field, following the flowering schedule. Once collected, the flowers should be arranged in layers of 15-20 cm in order to avoid mould.
The yields obtainable vary depending on the product. For the dried flower, realistic yields are between 800 and 1,500 kg/ha of selected dried flower heads. For the dried aerial part intended for extraction (flowers, stem and leaf), one hectare can yield up to 3,500 kg of product in irrigated conditions with 2-3 cuts. Seed yield can reach 600-800 kg/ha.
Nutritional values
Since ancient times, calendula has been known above all for its anti-inflammatory and vulnerary properties, and is therefore widely used in many topical preparations.
Calendula has a well-studied and substance-rich phytocomplex. Triterpene derivatives are predominant; saponosides such as oleanic acid glycosides, in fact, represent from 2 to 10% of the dry weight of the flowers. The content of carotenoids (1.5% ps) is important, including β-carotene, lycopene, lutein and xanthines in general, responsible for the yellow-orange color of the flowers. Flavonoids are also present, such as isorhamnetin glycosides. The content of essential oils is also interesting, which in fresh flowers is equal to 0.03%, while in leaves it reaches 0.7%.
Other important properties are antimicrobial, immunomodulatory, lipid-lowering and anti-ulcer.
Antitumor, bradycardic, choleretic, vasoprotective and spermicidal activities have also been demonstrated.
Biodynamics
We recommend flowering days for sowing, harvesting and processing. If you are transplanting, immerse the roots in water dynamited with 500 (horn manure) or spray 500 in the furrows, this will encourage strong rooting stimulation.
Cornosilica (501) is indicated for increasing the qualitative yield of inflorescences (phytocomplex content). To combat cryptogams we recommend thoughtful irrigation (no water stagnation), a planting layout that allows good ventilation and the use of horsetail.