How to grow basil in pots: complete guide

Most common varieties

Genovese basil: the classic pesto variety, large bright-green leaves, intense sweet aroma.

Neapolitan basil: even larger leaves, fresher aroma, good in salads.

Greek basil (or fine-leaf basil): compact, very branched plant, ideal for small pots and windowsills. Very resilient.

Red or purple basil: spicier aroma, decorative.

Thai basil (lemon, cinnamon): used in Asian cuisine, very different aromas from Genovese.

When and how to plant it

Basil fears cold: it suffers below 10°C and dies at the first frost. In temperate climates sow or plant out from mid-April (mild areas) to late May (colder areas), once the risk of night frost has passed.

You can start from seed (cheap but 2-3 weeks slower) or from a nursery seedling (faster). If you buy a supermarket "plant" with many small ones in a single pot, split them: too many plants in too little space will smother each other.

Pot and substrate

Pot at least 20-25 cm wide and equally deep for a single well-developed plant. If you plant multiple seedlings, allow 15-20 cm between them. Rectangular balcony planters work great for growing several plants together.

Substrate: quality all-purpose enriched with compost or a pinch of well-rotted manure. Add perlite to improve drainage. The pot must have drainage holes.

Light

Basil loves sun: minimum 5-6 hours of direct light per day. A south- or east-facing balcony works great. In too much shade it goes leggy, with small leaves and no aroma.

Watering

Basil drinks a lot in summer. Water when the top 2 cm is dry: in high summer that often means daily or every other day. Evening is better than morning (leaves aren't hit by immediate sun and roots have time to absorb).

Watch out: don't wet the leaves while watering, pour at the base of the plant. Wet leaves on cool evenings encourage downy mildew, the main basil disease.

Pruning: the key to continuous harvests

The secret to basil from June to November is regular pruning. Left alone, the plant produces flower spikes at the top of the stems, exhausts its energy on reproduction and stops making leaves.

The rule: as soon as the plant has 4-6 well-developed leaves, cut the main stem above the second pair of leaves from the bottom. The plant will respond with two new lateral shoots. Repeat every time a new stem reaches 4-6 leaves. In a few weeks you have a bushy plant full of leaves.

Remove every flower spike as soon as it appears: flowering interrupts leaf production and worsens the aroma.

Fertilising

Basil is a "hungry" plant: it consumes nutrients quickly. Feed every 15 days with a liquid vegetable fertiliser or diluted nettle liquid. In pots with little substrate, feeding matters even more.

Common problems

• Leaves yellowing from the bottom: overwatering or lack of fertiliser. Check drainage and feed.
• Leaves with black or brown spots: downy mildew. Remove affected leaves, space plants apart, avoid wetting foliage. In severe cases treat with copper.
• Holed leaves: slugs or snails. Set traps (a small dish of beer) or coarse-salt barriers around the pot.
• Aphids on apical shoots: strong water jet or diluted potassium soap.
• Leggy plant with no leaves: too little light. Move to direct sun.

End of season

Basil is an annual: with the first cool nights (below 12°C, typically October-November) it produces less and dies with the first frost. Before that, cut large bunches of leaves and freeze them (whole or in olive-oil cubes) to have them all winter.