Growing conditions Basil is sensitive to cold, with best growth in hot, dry conditions. Basil prefers high light conditions and grows best under full sun conditions. Increasing light intensity, particularly the
photosynthetic photon flux density, can significantly enhance the plant's fresh weight, dry matter content, and height. However, due to its common use, basil is cultivated in many countries around the world. Production areas include countries in the Mediterranean area, those in the
temperate zone, and others in
subtropical climates. In Northern Europe, Canada, the northern states of the U.S., and the South Island of New Zealand, basil grows 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); however, it can also thrive when planted outside in these climates. Additionally, it may be sown in soil once chance of frost is past. It fares best in well-drained soil with direct exposure to the sun. Although basil grows best outdoors, it can be grown indoors in a pot and, like most herbs, will do best on a sun-facing windowsill, kept away from cold drafts. A
greenhouse or
row cover is ideal if available. It can, however, even be grown in a basement under fluorescent lights. Supplemental lighting produces greater biomass and
phenol production, with red + blue specifically increasing growth and flower bud production. increases the
volatiles in
O. basilicum essential oil, which has not been reproducible in other plants, and so may be unique to the genus or even to this species. Basil prefers well-drained organic soils, as adequate oxygen availability in the root zone is essential for optimal plant growth. Poor soil drainage can lead to root hypoxia, which negatively affects overall plant development and essential oil yield.
Pruning, flowering, and seeding foraging Once a stem produces flowers, foliage production stops on that stem, the stem becomes woody, and essential oil production declines. To prevent this, a basil-grower may pinch off any flower stems before they are fully mature. Because only the blooming stem is so affected, some stems can be pinched for leaf production, while others are left to bloom for decoration or seeds. 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. Once the plant is allowed to flower, it may produce seed pods containing small black seeds, which can be saved and planted the following year. If allowed to go to seed, a basil plant will grow back the next year.
Propagation methods Seeds The optimal germination temperature for basil seeds ranges between 34.5–39.0°C, while the base germination temperature lies between 9.8–13.2°C. No significant variation in optimal germination temperature has been observed among different basil cultivars. Prior to sowing, basil (
Ocimum basilicum) seeds can be hydroprimed by soaking in water for 12 hours, which effectively enhances germination rates and seedling vigor.
Cuttings Basil (
Ocimum basilicum L.) is commonly propagated through cuttings. Compared to seed propagation, basil cuttings tend to result in earlier harvest and higher yield. The typical propagation method involves selecting healthy, non-lignified stem segments approximately 5–10 cm in length, preferably apical shoots that retain 2 to 5 leaves, which are then inserted into moist soil until root development occurs. After rooting, the plantlets are transplanted into the field. Exposing basil cuttings to blue light significantly accelerates root formation, thereby shortening the growth period.
Diseases Basil suffers from several plant pathogens that can ruin the crop and reduce
yield.
Fusarium wilt is a soil-borne fungal disease that will quickly kill younger basil plants.
Seedlings may be killed by
Pythium damping off. A common
foliar disease of basil is
gray mold caused by
Botrytis cinerea; it can cause infections post-harvest and is capable of killing the entire plant.
Black spot can be seen on basil foliage and is caused by the
fungi genus Colletotrichum.
Downy mildew caused by
Peronospora belbahrii is a significant disease, as first reported in Italy in 2003. It was reported in the Florida in 2007 and by 2008 had spread along the eastern United States, reaching Canada. Basil cultivars resistant to
P. belbahrii have been developed. Non-pathogenic bacteria found on basil include
Novosphingobium species. ==Uses==