Tulsi (Holy Basil)

What is tulsi?

Tulsi is a basil, but not the one of pesto and tomato salad. It grows into a small, branched, somewhat woody bush, carries long spikes of pale pink or purplish flowers for much of the year, and its leaves smell warm and spicy, of clove and pepper. In India it is less a herb than a presence: a plant kept at the centre of the house, tended daily and treated with reverence.

Origin and growth

Ocimum tenuiflorum is native to tropical and subtropical Asia, from India and Sri Lanka through Southeast Asia to the western Pacific. It grows mainly in the seasonally dry tropics. Kew describes it as a perennial or subshrub; NC State Extension gives a height of about one metre, with stems and leaves often tinged purple. It has been introduced elsewhere, for example to Cuba, the Bahamas, Kenya and Zambia. Green forms (Rama or Vana tulsi) and purple-leaved forms (Krishna tulsi) are distinguished; the purple ones contain more phenolic compounds.

Requirements

Cold. Frost-tender. Indian cultivation guidance calls it highly sensitive to frost, says it must be protected from temperatures close to freezing, and gives 22 to 28 °C as ideal.

Water. Regular but moderate; in hot, dry weather it needs watering.

Soil. Well drained, moderately fertile. Waterlogging is harmful.

Light. Full sun.

Leaves and harvest

Leaves and flowering tips can be picked throughout the warm season. Regular picking keeps the plant bushy. The leaves are used fresh or dried, as a tea and, in Thailand, as a cooking herb. Their aroma comes largely from eugenol, the same compound that gives clove its scent.

Constituents and effects

Tulsi is one of the central plants of Ayurveda, where it is used as a daily tea and in remedies for coughs, fever, digestion and skin. This is a tradition of many centuries, not a clinical finding.

The human evidence has grown in recent years. A systematic review by Jamshidi and Cohen (2017) collected 24 studies with a total of 1,111 participants in which tulsi alone was given to people. They reported favourable changes in blood sugar, blood lipids and blood pressure, in immune markers and in measures of stress, sleep and mood; in a six-week placebo-controlled trial with 150 adults, stress-related symptoms decreased. No study reported significant side effects, though the longest lasted only 13 weeks. The studies were, however, mostly small and used different doses and preparations; the authors themselves called for further research on dosage, preparation and the groups most likely to benefit. Small clinical trials cited in a 2014 review found that rinsing with tulsi reduced Streptococcus mutans, a common bacterium of dental plaque, about as well as chlorhexidine or Listerine.

Other reported effects, against microbes, radiation damage or toxins, rest so far on animal and laboratory studies. In animal studies high doses reduced the implantation of fertilised eggs and the number of pregnancies carried to term. Whether this applies to humans is unknown; the Merck Manual advises against tulsi preparations for people trying to conceive, and in pregnancy it is used with caution.

In the food forest

In a food forest tulsi belongs to the herb layer. It flowers over a long season and is visited by bees and other insects. Its strong scent fits well into plant guilds around young fruit trees and into a herb spiral on its warm, dry upper part. As a short-lived perennial it fills gaps quickly and gives way when the shade of the trees closes.

In the Mediterranean climate

Published experience of tulsi as a field plant around the Mediterranean is scarce; in most gardens there it is grown as a summer plant from seed. The Mediterranean summer suits its love of heat and sun, provided it gets some water. The limiting factor is winter frost. NC State Extension notes that it self-seeds readily and is considered weedy outside its native range; in Europe it is not considered invasive and is not on the EU list of invasive alien species.

Propagation and care

Tulsi is sown in warm soil in spring, the small seeds only lightly covered. Cuttings root easily in water or moist soil. Pinching the tips keeps the plant compact; a few flower spikes are left to set seed.

How Terra Humana understands it

At Sa Medada tulsi is meant to bring scent, flowers and insects into the herb layer near the young trees. It is also a plant that people in another part of the world hold sacred, and we grow it with respect for that tradition.