Every year, the International Herb Association names a medicinal, culinary, or decorative plant Herb of the Year and their 2017 choice is coriander.
The exact origins of coriander (Coriandrum sativum) are lost in the mists of time, because the plant was already widely disseminated throughout much of the Old World well before the modern age. However, ethnobotanists believe it originally grew wild in the Mediterranean basin and the Middle East. It was certainly known to the ancient Egyptians and Greeks as well as to the Romans.
The name coriander is also of uncertain origin, but one of the more intriguing suggestions is that it derives it from the Ancient Greek kóris for stink bug, said to have a similar smell.
Coriander is quite typical of plants in its family, the Apiaceae, with a rosette of deeply cut leaves at the base giving rise to a leafy upright stem topped by domes of small flowers.
It’s an annual that reaches about 1 to 2 feet (30–60 cm) in height, sometimes more. The leaves that form the rosette are the ones usually harvested. They are medium green and fairly broad, diversely lobed with a toothed margin. In the rosette phase, it looks quite a bit like its close relative, parsley (Petroselinum crispum), and indeed is sometimes called Chinese parsley. The leaves of the top of the plant are more finely cut, giving maturing plants a very feathery appearance.
The flowers are borne at the top of the plant in small umbels. The tiny flowers are white or very pale pink. Those on the outside of the umbel bear asymmetrical petals, distinctly longer than the others. They do an excellent job of attracting pollinating and beneficial insects to the garden, especially hoverflies and ladybugs.
Even before the flowering has finished, the foliage will already be yellowing. The seed capsules mature rapidly and release their seeds, then the plant dies.
One Plant, Two Names
Northern Europeans mainly use dried coriander seeds as a condiment, a tradition that was also adopted in northern North America and Australia, while in Asia and South and Central America, populations mainly harvest the foliage.
Currently, under the influence of Mexican cuisine, the use of leaf coriander is gaining ground in North America under its Spanish name cilantro. In supermarkets, you usually see the Spanish name. Most people probably don’t realize coriander and cilantro are the same plant, just harvested at two different periods.
Besides being used as a culinary herb, both leaves and seeds of coriander are used medicinally, especially to treat gastric problems. Seeds also give an essential oil used in aromatherapy, perfumery and the food industry.
Of Questionable Taste
Curiously, the leaves and seeds don’t have the same flavor.
The leaves, used extensively in Asian and Mexican cuisines, have a refreshing taste a bit like parsley with a lemon bite to it, but it is certainly not everyone’s cup of tea. Many people say they taste and smell the soap… or worse! This disdain seems partially genetic and tends to run in families.
To my own nose, coriander leaves do indeed smell like a somewhat squashed stink bug… but then I find stink bugs, which obviously repel some people or they wouldn’t have that name, actually smell quite pleasant.
There is less controversy about the somewhat citrusy flavor of the seeds, which generally seem acceptable to all and are widely used in marinades and curries.
Novice gardeners often complain that they failed with coriander. But actually, they probably didn’t fail. They just didn’t understand that they have to harvest it promptly. Only a week or so goes by between the plant being ready to harvest and it turning brown and dying. You have to be fast when it comes to coriander!
That’s why I don’t recommend buying pots of already-started coriander, even though most garden centers (and supermarkets) sell them that way. Those plants are just about to bolt (go to seed) when you buy them and will probably do so shortly after you get them home. And as soon as they start to bolt, the foliage becomes bitter and is no longer edible. Why go through that?
It is far easier to sow this herb yourself from seed, sowing it directly in the ground where you want it to grow. Coriander seeds are widely available, probably in local garden centers; if not in just about any catalog that offers herb seeds.
Sow the seeds about ¼ inch (5 mm) deep and about 1 to 2 inches (3 to 5 cm) apart, starting in early spring, as soon as the soil can be worked. Repeat every 2–3 weeks: that way, you’ll have leaves to harvest throughout the summer and into fall.
You can also sow coriander outdoors in late fall to ensure the first harvest the following spring. In countries with mild winters, in fact, coriander is generally grown as a winter herb, as the cool days and even cooler nights (it will take some frost) help keep it from bolting.
The Laidback Gardener Method
The most laidback way to grow coriander is to let it self-sow.
The first time you grow it, simply let a plant or two go to seed. The seeds will then fall to the ground and germinate, providing a few seedlings at a time for most of the summer. From then on, let at least one plant go to seed each year and you’ll end up with a self-maintaining coriander supply, despite the very short life of each individual plant. Of course, you’ll discover that coriander doesn’t always sprout where you want it to, making it officially a weed… but at least it’s an edible weed!
Coriander prefers full sun or light shade and well drained, slightly acid soil (a pH of about 6.0 to 6.8) of just about any quality.
Coriander is rarely sown in rows. Instead, traditionally a few seeds are sown here and there among the other vegetables and herbs. It can also be sown in pots outdoors, normally near the edge of a pot containing other herbs or vegetables.
Thin the seedlings to 15 to 30 cm apart… and use the seedlings you remove by thinning in the kitchen as your first harvest.
Keep the soil slightly moist during the (very short) growing season. Covering the soil with mulch will keep the soil cooler and help delay bolting.
There is no need to go out of your way to fertilize coriander. Instead, just maintain good soil quality for the other herbs and vegetables and coriander will benefit from it.
Coriander grows best in spring and fall, but goes to seed rapidly in the heat of the summer. Sometimes you only have time to harvest a few leaves per plant from summer-grown coriander. Or simply harvest the seedlings as sprouts.
Coriander does not make a good indoor plant. Not only is it difficult find the intense sun and the cool temperature it prefers, but it’s sensitive to plant pests when grown indoors. Instead of trying to force a recalcitrant plant to grow to full maturity, though, try sowing and harvesting young plants before they start to degrade.
Sow the seeds in a pot or tray in moist soil, supplying the most intense lighting you can. The leaves will be small, but there should be plenty to harvest in just 3 to 4 weeks. Repeat sow every 2–3 weeks to ensure a continuous supply.
You can harvest coriander leaves at any time until the plant starts to bolt, from the time it is a seedling until it has formed its full rosette. Just cut off each leaf at the base. You can harvest up to one third of any given plant’s leaves at one time and it will replace them.
Coriander leaves don’t dry well. They can be frozen or stored in oil, but then lose a lot of their taste. It’s best to use them fresh.
As for the seeds, harvest them from the plants which you’ve allowed to go to seed. As soon as the capsules begin to turn brown, cut the stalks and place them inside a paper bag (some sources suggest they have to be upside down in the bag, but you can place them right side up or sideways: it makes no difference). Don’t wait too long to harvest them or the capsules will split open and you’ll lose the seeds!
The seeds are already dry when your harvest them and will readily keep for at least 4 or 5 years.
There are several varieties of coriander, but if you want to harvest leaves for the longest possible season, consider varieties that are known to be slow to bolt, such as ‘Calypso’, ‘Long-Standing’, ‘Marino’ or ‘Slow Bolt’. If growing for seed, though, these would be the worst choices!
Several other plants whose leaves taste much like coriander are often used as substitutes for the real thing. This is particularly the case with culantro (Eryngium foetidum), Bolivian coriander (Porophyllum ruderale) and Vietnamese coriander (Persicaria odorata, syn. Polygonum odoratum).