How to Grow Basil Indoors and Outdoors: A Complete Guide

Pick the basil that suits your kitchen

Sweet Genovese is the classic pesto basil — big tender leaves with a strong anise-and-clove flavour. If you cook Thai or Vietnamese food, grow 'Thai' or 'Siam Queen' for smaller, spicier leaves that hold up in hot dishes. Bush types like 'Spicy Globe' stay compact and barely need pinching, which makes them ideal for a windowsill. Purple varieties such as 'Dark Opal' grow more slowly and yield less, but look superb in a mixed container. Whichever you choose, buy named varieties rather than a generic packet just labelled 'basil' — flavour varies enormously.

Starting basil from seed

Basil germinates fast when it is warm: sow at 20-25°C and you will see sprouts in five to ten days. Press the seeds onto the surface of moist seed compost and barely cover them, because basil needs light to germinate and a thick layer of soil will stall it. Keep the tray humid with a clear lid or a plastic bag, but open it daily so mould does not take hold. Once seedlings have two true leaves, pot them on individually and bury the stem up to the first leaf pair. Basil grows quickly from seed, so a fresh sowing every four to six weeks gives you a continuous supply rather than one big flush.

Sun, soil and the right container

Basil is a hot-weather plant: give it at least six hours of direct sun, and it will sulk in shade. A south-facing windowsill or a sunny patio is ideal. In containers, use a free-draining potting mix rather than garden soil, and always pick a pot with drainage holes, because basil hates wet feet. In the ground, work in compost and plant only after the last frost, when nights stay above 10°C. Space plants 20-25 cm apart so air moves between them — crowded basil is the first to come down with downy mildew.

Watering and feeding

Water when the top 2 cm of soil feels dry, which in summer usually means every day or two. Water the soil rather than the leaves, and do it in the morning so the foliage dries before night; leaves that stay wet overnight invite fungal disease. Feed container basil every two weeks with liquid fertiliser at half strength. Do not overdo the nitrogen, because too much food makes lush leaves with almost no flavour. If leaves turn pale yellow while the veins stay green, that is a nitrogen shortage — a light feed will correct it within a week.

Pinch, don't just pick

The single best thing you can do for basil is pinch out the growing tip as soon as a stem carries three or four leaf pairs. Pinching just above a leaf node forces the plant to branch, turning one skinny stem into a bushy plant with far more leaves. Always harvest from the top down, and never strip more than a third of the plant in one go. The moment flower buds appear, pinch them off — once basil flowers, leaf production drops and the taste turns bitter and peppery. If you want seed for next year, let one plant flower at the end of the season and collect the dried seed heads.

Common problems

Downy mildew shows as yellow patches on the upper leaf surface and fuzzy grey growth underneath, and it spreads fast in cool, damp, crowded conditions. Remove affected leaves immediately and improve airflow, because badly hit plants rarely recover. Leggy, pale plants are usually short of light rather than short of food. Slugs and earwigs nibble holes in outdoor basil, so check under pots and mulch by torchlight after rain. Basil is frost-tender: below about 10°C it can blacken overnight, so bring pots indoors well before the first cold night.

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