Coriander

Light and exposure

For a leaf harvest, coriander prefers a partly shaded position, especially in high summer. A spot that is too hot and too sunny drives it to bolt almost at once, at the expense of foliage.

If your aim is instead to harvest the seeds, a sunny position promotes flowering and ripening. For foliage, then, give it a cool, bright corner that is not scorching, with light shade in the afternoon during heat waves.

Watering

Coriander needs constantly cool soil. The slightest water stress, soil that dries out or a burst of heat, triggers bolting, that is the rapid appearance of the flower stalk at the expense of the leaves. So water regularly to keep the soil cool.

In pots as in open ground, consistency is essential: frequent, moderate watering is better than a drying out followed by a flood. A light mulch at the base helps retain moisture and delay bolting.

Soil and repotting

Coriander likes loose, cool soil, rich in organic matter and well drained. Adding mature compost before sowing supports fast growth and abundant foliage.

It develops a taproot and tolerates transplanting poorly: it is better to sow it directly in its final spot rather than transplant it, which stresses it and speeds up bolting. In pots, choose a fairly deep container, at least twenty centimetres, with good drainage.

Temperature and humidity

Coriander is an annual that does not overwinter outdoors: it does not survive frost and completes its cycle in a single season. Unlike thyme, chives or mint, which are perennial and hardy, it must be resown every year. Unlike basil, it is not so cold-sensitive as to fear the slightest coolness: it tolerates mild temperatures and even grows better in the cool than in the heat.

It is precisely the heat that upsets it. A hot summer sends it to seed within a few days. So it can be sown relatively early in spring, as soon as the soil warms up a little, and again at the end of summer to make the most of the cool late season, when it produces fine foliage. An autumn frost marks the end of the plants in place.

Pruning and upkeep

Harvest the outer leaves as needed, cutting the stems at the base, which encourages the centre to produce new leaves. Pick regularly to slightly delay bolting and prolong the harvest.

As soon as a flower stalk rises in the centre, the plant switches to seed and the leaves become sparse and finely cut. You can cut this stalk to gain a few leaves, but a bolting plant is nearing the end. The best thing then is to let it flower to harvest the seeds, and to rely on a new sowing for foliage.

Pests and diseases

Coriander is fairly little affected by diseases, its short cycle often keeping it out of harm’s way. In damp weather, powdery mildew may cover the foliage with a white felt and leaf spots may appear. Thin out sowings that are too dense and avoid wetting the foliage in the evening to limit these troubles.

Like other Apiaceae, it can attract the carrot fly, Psila rosae, whose larvae attack the roots: an insect-proof mesh protects the sowing. Aphids sometimes nestle in the flower umbels, and slugs devour the young seedlings in spring. Nothing very serious in general on a crop grown cool and airy.

Propagation

Coriander is propagated only by sowing, and preferably by direct sowing, since it hates transplanting. Sow the seeds about one centimetre deep, in cool, loose soil, in their final position. Emergence takes one to three weeks. A classic trick is to split or lightly rub the seeds, which are in fact double fruits, to speed up germination.

Stagger the sowings every two or three weeks, from spring to the end of summer, to make up for the rapid bolting and have leaves continuously. If you let a plant flower and set seed, it often self-sows and you will find spontaneous seedlings the following season.

Month-by-month care calendar

Green Hub tips

• Always sow in place, without transplanting: coriander’s taproot hates being disturbed and this triggers bolting.
• Against too-rapid bolting, keep the soil cool and give it partial shade in summer. A burst of heat or dryness sends it running.
• Stagger the sowings every two to three weeks: a plant produces leaves for only a limited time before bolting.
• The best foliage comes in the cool of spring and autumn. A late-summer sowing benefits from a mild late season.