Basil (Ocimum basilicum)

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Native to tropical regions from Central Africa to Southeast Asia, basil is a culinary herb typically used in cuisines worldwide. There are many varieties of basil, most of the common ones being grown as annuals while some others are treated as perennial in warm, tropical climates. Basil is highly revered in Hinduism and was believed to open the gates of heaven for a person passing on among ancient Egyptians and Greeks. It is often used in gardens to repel various insects and deter mosquitoes.

Basil is known to have therapeutic properties, and has been used for thousands of years as a medicinal herb in Ayurveda and traditional Chinese medicine. It acts principally on the digestive and nervous systems, easing flatulence, stomach cramps, colic and indigestion.

Growing recommendations

Basil grows best in well-drained, moist, light (sandy) and medium (loamy) soils, and tolerates a pH ranging from 5 to 8. Perennial in the tropics, it is frost tender and needs to be grown as a half-hardy annual in temperate zones. The plant prefers heat, and usually requires six to eight hours of full sun each day, which will also help to reduce the apparition of diseases. In hottest climates however, basil can be grown in a partially shaded area. It flowers from August to September and the seeds ripen in September.

Basil may be started from seed indoors about six weeks before the last spring frost then transplanted in the garden one month and a half thereafter or direct seeded in warmer climates. They will germinate within 10-14 days at an optimum temperature of 20-25° C. Plants meant for seed production should be thinned out to 25 cm. Varieties that grow larger and bushier might benefit from being staked. Some will self-seed easily in the garden if allowed to.

Common diseases and pests

• Fungal diseases: Cercospora leaf spot (Cercospora ocimicola), downy mildew (Peronospora belbahrii), fusarium wilt (Fusarium oxysporum), gray mold (Botrytis cinerea), leaf spot (Pseudomonas cichorii, Colletotrichum spp.), root rot (Rhizoctonia solani, Pythium spp.).
• Insect pests: Aphids (various spp.), cutworms, loopers, owlet moths, and underwings (Spodoptera exigua, Trichoplusia ni, and others), flea beetle (Phylotreta spp.), grasshoppers (various spp.), Japanese beetle (Popillia japonica), leafminers (Liriomyza spp.)
• Nematodes: Root knot nematode (Meloidogyne spp.)

Pollination, crossing, and isolation

Basil bear hermaphrodite flowers that require insects – especially bees – to be pollinated. Cross-pollination is possible between different varieties, but seed purity can be maintained by isolating each one of them by 50 m. In the event several different varieties are grown simultaneously, an alternate day caging system can be used in order to prevent any crossing.

General seed saving guidelines (harvesting and processing)

Basil flower racemes – which are flower clusters with the separate flowers attached by short equal stalks at equal distances along a central stem – will mature gradually from the bottom to the top of the stem. The stem can be cut when the inferior seed capsules start to turn brown and put to dry in a ventilated area away from the direct sun. The plant will nonetheless continue to produce flowers and seeds.

Each flower contain four small seeds that are sometimes difficult to extract. They can be separated from the racemes over a bowl by using your fingers to crumble the dried head or rubbed against a fine wire mesh. The bowl is carefully swirling around so the seeds can stay at the bottom and to allow the chaff to come on top and be raked off. The remaining chaff is then winnowed either by blowing or using a fan on a very low setting (the seeds are light and can be blown away easily).

Basil seeds will remain viable for an average of five years when stored under optimum conditions.