Basil

How to recognise it

Growth form

Upright, branched annual of 20–60 cm, with square stems like all members of the mint family.

Leaf

Opposite, oval to broadly lance-shaped, 2–10 cm long, glossy green or purple, with an entire or slightly toothed edge. Rub one and you smell the typical sweet, spicy scent.

Flower

Small white, pink or pale purple lipped flowers of about 1 cm, in whorls stacked into a spike at the tips of the stems, from July to September.

Fruit/Seed

Four small black nutlets per flower, inside the persistent calyx. Wet seed develops a coat of jelly and swells.

Roots

Fine, branched and shallow: in a pot it dries out quickly, and it hates waterlogged roots.

Confusion with

Related species such as holy basil (Ocimum tenuiflorum) and lemon basil look very similar but smell and taste different. So read the label if you are after a particular flavour.

Flowering: July–September · Pruning: June–September

Why grow it?

• One of the most popular culinary herbs: fresh leaves flavour tomatoes, pasta, pesto, soups and salads.
• Flowers from July to September with small, nectar-rich lipped flowers that honeybees, bumblebees and solitary bees love.
• Easy to grow from seed on a sunny windowsill, a balcony or a patio: you do not need a garden.
• There are dozens of varieties with different flavours and colours: large-leaved, small-leaved, purple, lemon- or aniseed-scented.
• A handsome, fragrant plant in a pot next to the tomatoes or among summer flowers.

Basil: where does it grow best?

• Native to warm, tropical parts of Asia; it does not grow anywhere in the wild here.
• Full sun and warmth: a south-facing window, a sheltered patio or a spot against a sunny wall. Below 10 °C it hardly grows.
• Light, humus-rich, free-draining compost or garden soil that stays moist but never soggy.
• Sheltered from wind and heavy rain; in cool, wet summers it does better in a greenhouse or on a windowsill.

Goes well with

• Tomato: Same need for sun, warmth and regular water, and a classic pairing in the kitchen.
• Sweet pepper: Another warmth lover, for the vegetable patch, the greenhouse or a pot on the patio.
• Parsley: Another leafy kitchen herb, which tolerates a little more shade.
• Pot marigold: Orange flowers among the vegetables that also attract hoverflies and bees.
• Nasturtium: Tumbles cheerfully over the edge of a container next to the basil.

Basil: when and how to plant it?

1. Sow indoors from April in small pots or a seed tray of fine seed compost, somewhere warm at 20–25 °C. Press the seed down and cover it only very thinly.
2. Keep the compost moist, not wet. The seed germinates in 1–2 weeks; move the seedlings straight into good light, or they become leggy and floppy.
3. Prick out the seedlings in groups of 3–4 into a 10–12 cm pot as soon as they have two true leaves.
4. Only put plants outside after mid-May, when nights no longer drop below 10 °C, 20–30 cm apart. Harden them off first for a week by putting them out during the day.
5. A supermarket pot holds dozens of seedlings: split the root ball into 3–4 pieces and pot each one into a larger pot with fresh compost.
6. Water in the morning, at the base rather than over the leaves, and let the top centimetre of soil dry out in between.

Care

Water

Regularly but in moderation: it likes moist, not wet, soil. Check pots almost daily in summer.

Feeding

In a pot, a little organic liquid feed or some compost every two to three weeks. Too much feed gives soft leaves with less flavour.

Harvesting

Always cut whole tips just above a pair of leaves rather than picking single leaves: this makes it branch and stay compact.

Flowers

Pinch out flower buds if you mainly want leaves. Let a few plants flower for the bees and for your own seed.

Warmth

Bring pots indoors on a cold night. Below 5–10 °C it gets black patches and stops growing.

Tip: Do not keep fresh basil in the fridge, as it turns black: stand the stems like a little bouquet in a glass of water on the kitchen worktop.

Pruning and mowing

Pruning months: June–September.

When: From June to September, every time you harvest: pinching out the tips keeps the plant compact and leafy.

How:

• Pinch or cut out the tip of young plants above the third or fourth pair of leaves so that side shoots form.
• After that, always harvest the tips of the stems, just above a pair of small side buds.
• Remove flower spikes as soon as they appear if you mainly want to harvest leaves.
• In August, let a few stems flower: bees feast on them and you can collect seed.

Caution: Do not just pick the large lower leaves: the plant then grows tall and bare and runs to flower sooner.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow indoors in April–May at 20–25 °C. You can collect seed from your own plants in September, but varieties can cross with each other and will then not come true.

Cuttings

From June to August: cut an 8–10 cm tip without flower buds, remove the lower leaves and stand it in a glass of water or in moist cutting compost. It roots within 1–2 weeks.

Basil: how does it get through the winter?

Hardy to 5 °C: protect in harsh winters.

• Basil is not hardy: the first night frost, and even a few cold nights below 5 °C, are enough to kill it.
• Outdoors it dies in October; pull the plant up then and put it on the compost heap.
• A pot on a warm, sunny windowsill keeps giving leaves for a few weeks, but it grows poorly in the dark winter months. Cuttings taken in September overwinter indoors more easily.
• In autumn, freeze chopped leaves with a little olive oil in an ice-cube tray, or make a stock of pesto.

Diseases and pests

• Damping off: Seedlings collapse and rot at the base. Sow in clean seed compost, not too thickly, and do not overwater.
• Slugs: Outdoors they can eat young plants in a single night. Grow in pots on a table or patio and check in the evening.
• Downy mildew: Leaves turn yellow with a greyish-purple fuzz underneath, mainly in wet summers. Water at the base, space the plants out and remove diseased plants.
• Aphids and whitefly: Mainly indoors and in the greenhouse. Spray them off with water or wipe them away; outdoors, ladybirds and parasitic wasps help.
• Black leaves: Cold damage or waterlogged roots. Move the plant somewhere warmer and let the soil dry a little between waterings.

Through the year

• March: Buy seed. With a warm, light spot you can already sow indoors at the end of March.
• April: Sow indoors at 20–25 °C.
• May: Prick out the seedlings. After mid-May, put plants outside in a warm spot.
• June: Pinch out tips and make the first harvest. Take cuttings.
• July: Harvest freely. The first flower spikes appear.
• August: Harvest and make pesto. Let a few plants flower for the bees.
• September: Collect seed. Last big harvest; freeze leaves.
• October: Outdoor plants die with the first cold. Bring a pot indoors onto the windowsill.

Did you know?

• The name comes from the Greek basilikon, ‘royal’: it was considered a herb fit for a king.
• In water, basil seed develops a coat of gel and swells into little balls that look like frogspawn; in parts of Asia it is added to sweet drinks and desserts.
• Purple varieties owe their colour to anthocyanins, the same pigments found in red cabbage.