The Weed That Invented Mustard — Korea's Wild Mustard and the Kimchi That Made a City Famous

 The Weed That Invented Mustard — Korea's Wild Mustard and the Kimchi That Made a City Famous

The yellow condiment in the plastic squeeze bottle on the diner table. The grainy Dijon that comes in a small glass jar. The hot English mustard that clears the sinuses in a single bite. All of them trace back to plants in the same botanical family as this one — small, yellow-flowered, growing in fields and roadsides across the temperate world, entirely unremarkable to most people who walk past them.

들갓 is wild mustard. *Sinapis arvensis*, or its close relative *Brassica juncea* — the two are so similar that even trained botanists sometimes argue about which one they're looking at. Both produce the same four-petaled yellow flowers arranged in a cross, the same long slender seed pods, the same pungent seeds that, when ground and mixed with liquid, produce mustard.

The cross-shaped flower is so consistent across the entire family that botanists named it after the shape: Cruciferae, the cross-bearers. The name has since been updated to Brassicaceae, but the observation stands. Every cabbage, broccoli, radish, arugula, wasabi, and horseradish plant on earth belongs to this same family of cross-shaped flowers.

 The Plant: 들갓 (Sinapis arvensis / Brassica juncea group)

**Korean name:** 들갓 (wild mustard); 갓 (cultivated mustard)  

**English common name:** Wild Mustard, Charlock, Indian Mustard  

**Scientific name:** *Sinapis arvensis* L. / *Brassica juncea* (L.) Czern.  

**Family:** Brassicaceae (십자화과)  

**Blooms:** April – June  

**Height:** 30–80cm  

**Native range:** Mediterranean/Western Asia; now distributed worldwide  

**Toxicity:** None. All parts edible.

들갓 is an annual or winter annual herb — a weed of cultivated ground, field margins, and disturbed roadsides. It germinates in autumn or spring, grows quickly, flowers prolifically, sets seed, and dies. The stems are bristly with stiff hairs. The lower leaves are large and lobed; the upper leaves smaller and often clasping the stem. The flowers are bright yellow and produced in elongating racemes at the stem tips — as older flowers go to seed, new ones continue opening above them.

The seed pods are long and narrow, ending in a beak-like tip. When the pods ripen and dry, they split open and fling the seeds. A single plant can produce over 2,000 seeds, which is one reason wild mustard has followed human agriculture to every continent.

 The Mustard Plant, Historically Speaking

Mustard as a condiment is ancient. Roman recipes include it. Greek texts describe it. The Sanskrit word for mustard appears in texts dating back thousands of years. What people were using in all of these contexts was the ground seed of *Brassica* or *Sinapis* species mixed with liquid — grape must in Rome (giving us the word "mustard": *mustum ardens*, burning must), vinegar in medieval Europe, water in various Asian traditions.

The pungency of mustard — that sharp, sinus-clearing heat — comes from compounds called glucosinolates. In the intact seed, they're chemically inert. When the seed is crushed and mixed with water, an enzyme called myrosinase becomes active and converts them into isothiocyanates — the compounds that produce the heat. This is why ground dry mustard powder doesn't smell particularly pungent until you add water and wait a few minutes. The heat develops as the chemical reaction proceeds.

Yellow mustard (the American diner variety) is mild because it uses *Sinapis alba* seeds and adds turmeric for color. Dijon uses brown or black mustard seeds (*Brassica nigra* or *B. juncea*) and white wine instead of vinegar, which produces a sharper flavor. English mustard uses a blend. The variation in mustard flavor across cultures is largely a variation in which species of seed, and what liquid was used to mix it.

 갓김치 — The Kimchi That Put Yeosu on the Map

In Korea, 갓 — the cultivated form of mustard greens — is most famous not as a condiment but as a kimchi ingredient. And 갓김치 from Yeosu, the coastal city in South Jeolla Province, is considered the finest in the country.

The 갓 grown in Yeosu has a particular character that local farmers attribute to the sea air and the specific mineral content of the coastal soil. The leaves are more tender than inland varieties, the pungency balanced rather than overwhelming, and the fermented result has a depth of flavor that 갓김chi from other regions supposedly doesn't quite match. This is the kind of claim that sounds like local boosterism but is taken seriously enough by Korean food culture that Yeosu 갓김치 has become an explicit regional identity marker — something the city is actually known for.

갓 leaves, like all Brassicaceae, contain glucosinolates. In fermentation, these break down further and transform, producing the complex flavor that makes 갓kimchi different from cabbage kimchi. The fermentation period is shorter — 갓kimchi is often considered ready within a few days to a week, where baechu kimchi benefits from longer aging. The result is sharper, more immediately pungent, with a fresh bite that doesn't mellow the way cabbage does.

 What the Seeds and Leaves Do Medicinally

In traditional Korean and East Asian medicine, 갓 seeds — 개자 (芥子) — were a genuine pharmacological ingredient, not just a kitchen spice.

The seeds were used externally as a rubefacient: ground and made into a poultice, they cause skin reddening and warmth, and were applied to joints, the chest, and the back to treat rheumatic pain, bronchitis, and cold-type conditions. This is the same application that gave us "mustard plasters" in Western folk medicine — a centuries-old parallel use on opposite sides of the world for the same plant family.

Internally, the seeds were used to promote digestion, warm the stomach, and expel cold and dampness from the body. The young leaves were eaten as a spring 나물 — peppery and pungent, eaten blanched or raw. Modern analysis confirms that mustard greens are genuinely nutritious: high in vitamin K, vitamin C, folate, and the glucosinolates that in metabolized form have been associated with cancer-protective properties in epidemiological research.

 Finding It — And the Field in These Photos

In Korea from April through June, wild mustard appears wherever the ground has been disturbed. Field edges, roadsides, embankments, the margins of cultivated land. It grows tall enough to be conspicuous once it flowers — the yellow stands out against the green. The bristly stems and the elongating flower racemes with developing seed pods below and open flowers above are the field markers.

The cross-shaped four-petaled yellow flower is diagnostic for the family but not specific to this species — there are several other yellow Brassicaceae flowers in Korea at the same time of year. The combination of bristly stems, large lobed lower leaves, and the elongating raceme with seed pods already visible at the bottom while flowers continue opening at the top narrows it considerably.

One thing worth noting about the field in these photos: the dense, bright green feathery vegetation filling the background is 쇠뜨기 (*Equisetum arvense*, field horsetail) — one of the most ancient plant lineages on earth, a living relative of species that grew 350 million years ago before flowering plants existed. The fact that 들갓, one of the most modern and agriculturally successful weeds on the planet, grows alongside 쇠뜨기 in the same patch of disturbed ground is a quietly interesting collision of timescales. Both thrive in the same poor, disrupted soil — just for very different reasons and from very different points in evolutionary history.

 ⚠️ Disclaimer

This blog documents Korean plants and their traditional uses for educational and cultural purposes only. Nothing here is medical advice. Mustard seed poultices can cause skin irritation or burns if left on too long — traditional use required careful application and timing. If you're considering using any plant medicinally, consult a qualified healthcare provider first.

*Photographed in Korea, April 2026. All field photography by The Korean Herbalist.*

**Tags:** 들갓, 갓, Sinapis arvensis, Brassica juncea, wild mustard Korea, Korean mustard greens, 갓김치 Yeosu, Korean spring plants, Brassicaceae Korea, Korean traditional medicine