Basil (Ocimum basilicum, family Lamiaceae) is also known as St. Joseph's Wort and Sweet Basil. It is a tender low-growing herb, originally native to tropical Asia. It grows to between 20–60 cm tall, with opposite, light green, silky leaves 1.5–5 cm long and 1–3 cm broad. It tastes somewhat like anise, with a strong, pungent, sweet smell. Basil is very sensitive to cold, with best growth in hot, dry conditions. While most common varieties are treated as annuals, some are perennial, including African Blue and Holy Thai basil.
The word basil comes from the Greek βασιλευς, meaning "king", as it is believed to have grown above the spot where St. Constantine and Helen discovered the Holy Cross. The Oxford English Dictionary quotes speculations that basil may have been used in "some royal unguent, bath, or medicine". Basil is still considered the "king of herbs" by many cookery authors. An alternative etymology has "basil" coming from the Latin word basilicus, meaning dragon and being the root for basilisk, but this likely was a linguistic reworking of the word as brought from Greece.
Basil, the herb
Basil is most commonly recommended to be used fresh, and in cooked recipes, is generally added at the last moment, as cooking destroys the flavour quickly. The fresh herb can be kept for a short time in plastic bags in the refrigerator, or for a longer period in the freezer, after being blanched quickly in boiling water. Place fresh leaves in a dry jar with a pinch of salt, and cover with olive oil. The dried herb also loses most of its flavour, and what little flavour remains tastes very different, with a weak coumarin flavour, like hay. But because most Americans either lack the dedication or resources to maintain a supply of fresh herbs, the most common household use of basil in the US is through containers of dried basil purchased from stores.
Mediterranean, Thai, and Vietnamese cuisines frequently use basil, the former frequently combining it with tomato. Basil is one of the main ingredients in pesto — a green Italian oil-and-herb sauce from the city of Genoa, its other two main ingredients being olive oil and pine nuts. The most commonly used Mediterranean basil cultivars are 'Genovese', 'Purple Ruffles', 'Mammoth', 'Cinnamon', 'Lemon', 'Globe', and 'African Blue'. Chinese cuisine also uses fresh or dried basils in soups and other foods. In Taiwan, people add fresh basil leaves into thick soups (羹湯; gēngtāng). They also eat fried chicken with deep-fried basil leaves.
Basil is sometimes used with fresh fruit and in fruit jams and sauces — in particular with strawberries, but also raspberries or dark-colored plums. Arguably the flat-leaf basil used in Vietnamese cooking, which has a slightly different flavour, is more suitable for use with fruit.
When soaked in water the seeds of several basil varieties become gelatinous, and are used in Asian drinks and desserts such as falooda or sherbet. Such seeds are known variously as sabja, subja, takmaria, tukmaria, or falooda seeds. They are used for their medicinal properties in Ayurveda, the traditional medicinal system of India.
Several other basils, including some other Ocimum species, are grown in many regions of Asia. Most of the Asian basils have a clove-like flavour that is generally stronger than the Mediterranean basils. In China, the local cultivar is called 九層塔 (jiǔcéngtǎ; literally "nine-level pagoda"), while the imported varieties are specifically called 羅勒 (luólè) or 巴西里 (bāxīlǐ).
Basil is also very popular in Thai cuisine, which uses cultivars of two different species: the type known in the west as Thai Basil, which is a cultivar of O. basilicum, and Holy Basil (Ocimum sanctum).
'Lemon basil' has a strong lemony smell and flavour very different from those of other varieties, because it contains a chemical called citral. It is widely used in Indonesia, where it is called kemangi and served raw, together with raw cabbage, green beans, and cucumber, as an accompaniment to fried fish or duck. Its flowers, broken up, are a zesty salad condiment.
Basil thrives in hot weather, but behaves as an annual if there is any chance of a frost. In Northern Europe, the northern states of the U.S., and the South Island of New Zealand it will grow best if sown under glass in a peat pot, then planted out in late spring/early summer (when there is little chance of a frost). It fares best in a well-drained sunny spot.
Although basil will grow best outdoors, it can be grown indoors in a pot and, like most herbs, will do best on a south-facing windowsill (in the Northern Hemisphere). It should be kept away from any draughts, and must be able to get plenty of sunlight, therefore a greenhouse or cloche is ideal if available.
If its leaves have wilted from lack of water, it will recover if watered thoroughly and placed in a sunny location. Yellow leaves towards the bottom of the plant are an indication that the plant needs more sunlight or less fertilizer.
In sunnier climates such as Southern Europe, the southern states of the U.S., the North Island of New Zealand, and Australia, basil will thrive when planted outside. It also thrives over the summertime in the central and northern United States, but dies out when temperatures reach the low thirties, to grow again the next year if it was allowed to go to seed. It will need regular watering, but not as much attention as is needed in other climates.
Basil can also be propagated very reliably from cuttings in exactly the same manner as "Busy Lizzie" (Impatiens), with the stems of short cuttings suspended for two weeks or so in water until roots develop.
Leaf production slows or stops on any stem which flowers, so you can pinch off any flower stems to keep the plant in production, or pinch off some stems while leaving others to bloom for decoration or seeds. Once you do let the plant flower, it will produce seed pods containing small black seeds which you can save and plant the following year. Picking the leaves off the plant helps "promote growth", largely because the plant responds by converting pairs of leaflets next to the topmost leaves into new stems.