African Basil

About

African basil is the woody one. Where the other basils in this collection die at the end of a season, this is a tender perennial sub-shrub that will run for years under glass and reach nearly two metres in a warm climate.

The scent is clove rather than aniseed, from a high eugenol content, and it is strong enough that a plant scents a greenhouse. West African cooking uses it heavily, where it is scent leaf in Nigeria, efirin in Yoruba and nchanwu in Igbo, going into pepper soup, into stews and into the sauce served with yam.

In Britain it needs a greenhouse or a conservatory. It will spend the summer outside in a pot and it must come in well before the nights cool, because it suffers below 10 deg C and dies below about 5 deg C.

Appearance and character

A bushy upright sub-shrub, 60 cm to 1.8 m, going woody at the base from its second year.

Leaves are larger than most basils, 5 to 12 cm, oval, pointed, coarsely toothed and softly hairy, mid green and slightly wrinkled.

Flowers open in branched spikes at the shoot tips, small and greenish-white to pale yellow, held in whorls. They are less showy than the coloured spikes of holy basil.

Stems are square, hairy and green, turning brown and woody with age.

The scent is clove, sharp and penetrating, and it is much stronger than any of the annual basils.

An old plant makes a substantial shrub rather than a herb, which is why it is sometimes sold as tree basil.

Where it is from

African basil is native to tropical Africa and to south and south-east Asia, and it grows across both regions on disturbed ground and forest edges.

West African cooking is where it is used most. In Nigeria it is scent leaf, and it goes into pepper soup, into egusi and ogbono stews, and into the sauces served with yam and rice. Ghana, Cameroon and Benin all use it similarly.

In India it is one of the plants called tulsi, specifically vana tulsi or wild tulsi, and it is used in the same way as holy basil though with a lighter scent.

Its essential oil is extracted commercially in India, Africa and Brazil for its eugenol content, which competes with clove oil as a source of that compound.

It arrived in British horticulture through the seed trade rather than the nursery trade, and it is more often grown from seed here than bought as a plant.

How it grows

Sow indoors from March at 20 to 25 deg C. Surface sow and press the seed in.

Germination takes one to three weeks in warmth and can be uneven.

Prick out into small pots and grow on somewhere bright and warm.

Pot on into 25 cm pots as the plant grows. It gets large and it wants the room.

Take cuttings, which is the easier route once you have a plant. Softwood cuttings root readily in warm gritty compost, and this is how to keep a good plant going rather than resowing.

Grow it under glass. A greenhouse or conservatory suits it, and it will stand outside on a warm patio from late June to early September.

Pinch the tips to keep it bushy, and cut it back by a third in spring.

Keep it above 12 deg C through the winter, watering sparingly. It will drop some leaves and recover in spring.

Harvest leaves and shoot tips through the growing season.

Through the seasons

Winter is survival under glass. Keep it above 12 deg C, water sparingly and expect some leaf drop.

Spring brings new growth from April. Cut back by a third, repot, and take cuttings.

Early summer is when growth accelerates. Move it outside once the nights are reliably above 12 deg C, which is late June in most of Britain.

Midsummer is the main harvest. Pinch tips and cut shoots freely.

Late summer is flowering. Leave the spikes if you want seed, or pinch them out for leaf.

Early autumn is the deadline. Bring the plant back under glass in September, well before the nights cool.

Care difficulty

Moderate, and the difficulty is heat and overwintering rather than anything about the plant itself.

It is a true tender perennial. Keeping it through a British winter means keeping it above about 12 deg C, which needs a heated greenhouse or a warm room, and that is more than most people will do for a herb.

Taking cuttings each summer is the practical answer. A rooted cutting on a warm windowsill takes far less space than a two-metre parent.

Overwatering rots it, as it does every basil. Water in the morning and never leave it standing.

Greenhouse pests find it. Whitefly in particular takes to a soft-leaved basil quickly, and a biological control is the sensible answer on a food plant.

Given warmth it grows vigorously and produces a great deal of leaf.

Watering

Water in the morning, when the top 2 cm of compost has dried.

Water more generously in summer than any other basil here, since the plant is large and growing fast.

Reduce sharply from October and keep an overwintering plant barely moist.

Never leave the pot standing in water.

Use tepid water in winter.

Ventilate as well as watering under glass, since still humid air is what brings on mould.

Warning signs, diseases and pests

Whitefly builds up fast under glass, showing as small white insects rising in a cloud when the plant is disturbed, with sticky honeydew below. Use sticky traps and a biological control.

Aphids gather on the growing tips. Rub them off.

Spider mite produces fine stippling and webbing in a hot dry greenhouse. Raise the humidity and use a predatory mite.

Root rot from cold wet compost blackens the base of the stem and kills the plant.

Leaf drop over winter is normal on a plant kept cool, and heavy leaf drop means it is too cold.

Grey mould on crowded stems in still air needs thinning and ventilation.

Leggy growth means too little light.

Growing environment

Under glass in Britain. A greenhouse or conservatory, with a summer holiday outdoors from late June to early September.

Full sun and warmth. Minimum 12 deg C in winter and 18 deg C or more for good growth.

Free-draining compost in a large pot, or a greenhouse border.

pH around 6 to 7.

Ventilation matters as much as heat, because whitefly and mould both take hold in still humid air.

It gets large. Allow for a plant a metre and more across in a greenhouse, and prune it in spring to keep it manageable.

Feeding

Feed a balanced liquid feed every three weeks from May to August. This is a larger, more vigorous plant than the annual basils and it takes more.

Stop feeding from September so the growth firms before winter.

Avoid heavy nitrogen, which produces soft growth that whitefly finds and that carries less scent.

Repot into fresh compost each spring rather than feeding an exhausted pot.

Potash in late summer helps ripen the growth before winter.

Troubleshooting

It died over the winter. Too cold. African basil needs to be kept above about 12 deg C and it dies below 5 deg C. Take cuttings in summer and overwinter small plants on a warm windowsill instead.

Why does it smell of cloves? Eugenol, the compound that dominates clove oil. This species carries a great deal of it.

Is it the same as tulsi? It is one of the plants called tulsi, specifically vana tulsi. Holy basil, Ocimum tenuiflorum, is the main one. The scents differ, and this species is stronger and more clove-like.

The greenhouse is full of whitefly. They find soft-leaved basils quickly. Use sticky traps and a biological control rather than spraying a food plant.

It went woody and stopped producing leaf. Cut it back by a third in spring and take cuttings, since a young plant produces far more than an old one.

Can I grow it outside? Only from late June to early September in a warm sheltered spot, in a pot you can bring in.

How is it used in cooking? In west African soups and stews, added towards the end so the scent survives. It is strong, so use less than you would use sweet basil.