About Allium L.
Garlic is a perennial flowering plant in the genus Allium, native to Central Asia, South Asia, and northeastern Iran. It grows from a bulb, producing a tall, erect flowering stem that can reach up to 1 meter (3 feet) in height. Its leaf blade is flat, linear, solid, between 1.25–2.5 cm (0.5–1.0 in) wide, and ends in a sharp point. In the Northern Hemisphere, garlic produces pink to purple flowers from July to September. The bulb has a strong odor and is typically made up of 10 to 20 cloves. Cloves closest to the center of the bulb are symmetrical, while the surrounding outer cloves may be asymmetrical. Each individual clove is wrapped in an inner sheathing leaf, which is itself surrounded by layers of outer sheathing leaves. If planted at the correct time and depth, garlic can be grown as far north as Alaska. Garlic produces hermaphroditic flowers that are pollinated by butterflies, moths, and other insects. Garlic plants are generally hardy and are not affected by many pests or diseases. Garlic is reported to repel rabbits and moles. The California Department of Food and Agriculture runs a certification program to confirm garlic crops are free from nematodes and white rot disease, which is caused by Stromatinia cepivora. Both of these issues can destroy garlic crops and remain in soil indefinitely once introduced. Garlic may also develop pink root, a typically non-fatal disease that stunts root growth and turns roots pink or red; or leek rust, which usually appears as bright orange spots on plant tissue. Leek moth larvae attack garlic by burrowing into leaves or bulbs. Botrytis neck and bulb rot affects onion, garlic, leek, and shallot; while Botrytis allii and Botrytis aclada cause this disease in onions, Botrytis porri causes it in garlic. According to the University of California, initial symptoms of the disease usually start at the neck, where affected tissue softens, becomes water-soaked, and turns brown. In humid conditions, a gray, felt-like spore-producing growth forms on rotting scales, and mycelia may develop between scales. Dark brown to black sclerotia, the pathogen’s resting structures, may eventually form in the neck or between scales. After consuming garlic, its scent can linger in the human body, causing bad breath (halitosis) and body odor. This effect is caused by allyl methyl sulfide (AMS), a volatile liquid that is absorbed into the bloodstream during the metabolism of garlic-derived sulfur compounds. From the bloodstream, AMS travels to the lungs (and then the mouth, causing garlic breath) and the skin, where it is released through pores. Because digestion takes several hours, and AMS release takes additional hours, the odor effect can last a long time after eating garlic. Washing skin with soap only partially and imperfectly reduces this odor. Studies show drinking milk at the same time as eating garlic can significantly neutralize bad breath. Holding a mixture of garlic and milk in the mouth before swallowing reduces odor more effectively than drinking milk after eating garlic. Plain water, mushrooms, and basil may also reduce garlic odor, though the combination of fat and water in milk is the most effective. Garlic breath is also commonly said to be relieved by eating fresh parsley. Abundant sulfur compounds in garlic are also responsible for garlic turning green or blue during pickling and cooking. Under acidic or heated conditions, the sulfur-containing compound alliin reacts with common amino acids to form pyrroles, which are clusters of carbon-nitrogen rings. These rings can link together into polypyrrole molecules. Ring structures absorb specific light wavelengths, which makes them appear colored. A two-pyrrole molecule appears red, a three-pyrrole molecule appears blue, and a four-pyrrole molecule appears green, similar to chlorophyll which is also a tetrapyrrole. Like chlorophyll, these pyrrole pigments are safe to eat. Similar to the color change onion undergoes when cut, caused by reactions between amino acids and sulfur compounds, garlic can also turn green after being cut. The dry green folds in the center of a garlic clove have a particularly strong flavor and scent. Allicin is a sulfur compound produced when fresh garlic is crushed or chewed, and it breaks down to form other sulfur compounds: ajoene, allyl polysulfides, and vinyldithiins. Aged garlic does not contain allicin, but may have some activity from the presence of S-allylcysteine. Some people have allergies to garlic and other species in the genus Allium. Allergy symptoms can include irritable bowel, diarrhea, mouth and throat ulcerations, nausea, breathing difficulties, and in rare cases, anaphylaxis. Garlic-sensitive people test positive to diallyl disulfide, allylpropyldisulfide, allylmercaptan, and allicin, all of which are found in garlic. People with garlic allergies are often also sensitive to many other plants, including onions, chives, leeks, shallots, garden lilies, ginger, and bananas. Multiple reports of serious burns from topical garlic use for purposes including naturopathic treatments and acne treatment show that care must be taken for these uses, usually by testing a small area of skin with a low concentration of garlic. Based on numerous reported burns, including burns to children, topical use of raw garlic, as well as insertion of raw garlic into body cavities, is discouraged. Topical application of raw garlic to young children is particularly not recommended. The side effects of long-term garlic supplementation are largely unknown. Possible side effects include gastrointestinal discomfort, sweating, dizziness, allergic reactions, bleeding, and menstrual irregularities. Some breastfeeding mothers have found that after consuming garlic, their babies may feed more slowly, and also have a noticeable garlic odor. However, one experiment found that infants spent more time attached to the breast and sucked more when the breast milk smelled like garlic. If higher than recommended doses of garlic are taken alongside anticoagulant medications, this can increase the risk of bleeding. Garlic may interact with warfarin, saquinavir, antihypertensives, calcium channel blockers, quinolone family antibiotics such as ciprofloxacin, hypoglycemic drugs, and other medications. The American Veterinary Medical Association considers garlic toxic to pets. Garlic is easy to cultivate and can grow year-round in mild climates. While sexual propagation of garlic is possible, almost all cultivated garlic is propagated asexually by planting individual cloves directly in the ground. In colder climates, cloves are best planted about six weeks before the soil freezes, with the goal of allowing bulbs to grow only roots with no shoots emerging above ground. Harvesting takes place in late spring or early summer. Garlic plants can be grown close together, leaving just enough space for bulbs to mature, and can be easily grown in containers with sufficient depth. Garlic grows well in loose, dry, well-drained soils in sunny locations, and is hardy throughout USDA climate zones 4–9. When selecting garlic for planting, it is important to choose large bulbs to separate into cloves for planting. Larger cloves, paired with proper spacing in the planting bed, will result in larger mature bulbs. Garlic plants prefer soil with a high organic material content, but can grow in a wide range of soil conditions and pH levels. There are multiple varieties of garlic, most notably split into the hardneck and softneck subspecies. Garlic can be sensitive to day length, so the latitude where it is grown affects which type is suitable. Hardneck garlic is generally grown in cooler climates and produces relatively large cloves. Softneck garlic is generally grown closer to the equator and produces small, tightly packed cloves. Garlic scapes are removed to direct all of the plant’s energy into bulb growth; the removed scapes can be eaten raw or cooked. Consumed garlic may act as a mosquito repellent due to sulfur compounds circulating in the bloodstream, but there is currently no scientific evidence confirming this efficacy. Garlic has been used as traditional medicine in many diverse cultures, including Korea, Egypt, Japan, China, Rome, and Greece. In his Natural History, Pliny the Elder listed a range of conditions that garlic was considered beneficial for. In the second century, Galen praised garlic as the "rustic's theriac" (cure-all). 12th-century writer Alexander Neckam discussed garlic as a palliative to relieve the heat of the sun during field labor. In the 17th century, Thomas Sydenham valued garlic as an application for confluent smallpox, and William Cullen's 1789 Materia Medica found that garlic alone cured some cases of dropsy. The sticky juice found inside garlic bulb cloves is used as an adhesive for mending glass and porcelain. An environmentally friendly garlic-derived polysulfide product is approved for use in the European Union (under Annex 1 of Directive 91/414) and the United Kingdom as a nematicide and insecticide, including for control of cabbage root fly and red mite in poultry.
