Why the yellow-flowered choy sum is the heart of Chinese vegetable cooking

Gardening · Published 3 October 2026 Swipe more like this →

In short: Choy sum, or heart of the vegetable, is a staple of Chinese cuisine prized for its tender stems and vibrant yellow blossoms. Unlike its cabbage cousins, this mustard family member never forms a compact head, instead offering a delicate, leafy structure that thrives in specific soil conditions and quick growth cycles.

Known in Cantonese as choy sum and in Mandarin as caixin, this versatile green is a member of the Brassica genus. Its name translates literally to heart of the vegetable, reflecting its central role in culinary traditions across China and Japan. Botanically, it is classified as Brassica rapa var. parachinensis or Brassica chinensis var. parachinensis, distinguishing it from other leafy greens like gai lan through its unique flowering habit.

The plant is characterized by erect, fleshy stems that reach between 15 and 20 centimeters in height, though total plant height can span from 10 to 40 centimeters depending on the specific variety and environmental factors. A defining feature is the appearance of distinct yellow flowers, which typically emerge once the plant has developed seven to eight leaves or reached a height of approximately 20 centimeters. These flowers feature four oval to round petals and six stamens, eventually giving way to silique-structured fruits that can contain anywhere from 4 to 46 small, round seeds.

Cultivation of choy sum requires attention to soil chemistry, as the plant prefers a pH range between 5.6 and 7.5. Its root system is relatively compact, remaining within a 12-centimeter radius and depth. As an annual herbaceous plant, it does not form the dense heads associated with traditional cabbages, instead maintaining a simple or branched leafy structure. Whether blanched, stir-fried, or added to soups, the entire plant is edible, making it a highly efficient and valued crop for home and commercial growers alike.

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