Basil

Light and exposure

Basil wants warmth and sun. Give it the warmest, brightest spot you have: a very bright windowsill, a veranda, a small greenhouse or a sheltered corner of the terrace. It needs at least six hours of sun a day to develop its aromas.

Growing it in a pot has a real advantage: you can follow the sun and bring the plant in for the evening as soon as the nights turn cool. In open ground, save the warmest wall of the garden for it, the one that catches the midday sun and gives its heat back in the evening.

Watering

Basil needs a soil that stays fresh and moist, without ever being waterlogged. Water regularly, ideally in the morning, at the base of the plant and not on the foliage. Watering in the evening leaves the leaves damp all night and opens the door to disease, a real risk under a humid summer.

In a pot, the compost dries out quickly in high summer and can need water every day in hot weather. A basil that wilts at midday but perks up again in the evening is simply short of water at the hottest moment.

Soil and repotting

A rich, light, well-drained potting mix suits it perfectly, whether in a pot or in open ground. Add a little mature compost at planting to support rapid growth.

Basil hates having its feet in water. In a pot, a drainage hole and a layer of clay pebbles at the bottom prevent stagnation, which is particularly useful when the rains set in at the end of summer.

Temperature and humidity

This is the critical point of the whole crop. Basil grows well between 18 and 28 degrees and already suffers below 12 degrees: the leaves blacken and growth stops. It tolerates no frost at all.

Do not trust an early mild spell at the end of winter. Late frosts often come back several weeks after the first fine days: wait until your region’s average last-frost date is well past before moving anything into open ground, and keep a protective fleece within reach for the cool nights early in the season.

Pruning and upkeep

Pinch out the tops of the stems regularly, just above a pair of leaves. The plant then branches and becomes bushy instead of running up tall. The more you harvest by pinching, the more basil produces.

Remove the flower buds as soon as they appear. Once basil flowers, it puts its energy into seeds, the leaves become smaller and more bitter, and the plant declines. Cutting off the flowers clearly extends the harvest.

Pests and diseases

Basil downy mildew, caused by Peronospora belbahrii, is the most common disease in a humid climate. You recognise it by a yellowing on the upper side of the leaves and a greyish-purple felting on the underside. It spreads quickly in mild, damp weather, typical of a soft, rainy end of summer.

To limit it, give the plants plenty of air, space them out, water at the base in the morning and never on the foliage. Collar rot, encouraged by soil that is too wet, and the slug that loves young plants round out the list of troubles to watch for.

Propagation

Sowing is the simplest route. Sow indoors, in the warmth between 18 and 22 degrees, from March onwards, on the surface because the seeds need light to germinate. Emergence takes one to two weeks.

Basil also roots very easily from cuttings: cut a stem ten centimetres long, remove the lower leaves and place it in a glass of water. Roots appear in one to two weeks, and you can then pot it up. A handy trick for multiplying a shop-bought plant.

Month-by-month care calendar

Green Hub tips

• Never move basil outside before your region’s last-frost date has passed. An early mild spell is a trap, late frosts come back after it.
• Always water at the base and in the morning. Wet leaves in the evening, under a humid summer, invite downy mildew.
• Cut off the flowers as soon as they show. Once it has gone to seed, basil turns bitter and stops producing.
• To multiply a fine bunch from the market for free, put a stem in water: it roots in two weeks.