Choy Sum, often marketed as Chinese flowering cabbage, is a popular Asian green celebrated for its tender stems and slightly sweet, mustardy flavor. This member of the Brassica family is harvested primarily for its flowering shoots, which are a staple in stir-fries, soups, and steamed dishes across East Asian cuisines. Successful cultivation requires attention to its preference for cooler conditions to prevent premature flowering, a process known as bolting.
Preparing the Planting Site
Choy Sum is a cool-season crop that thrives in moderate temperatures, ideally between 59°F and 77°F. Planting should be timed for early spring or late summer to early fall, allowing the plants to mature before intense heat or hard frost. High temperatures cause the plant to “bolt,” or send up a flower stalk, which reduces the tenderness and flavor of the harvest.
The planting site requires rich, well-draining soil to support the plant’s rapid growth and shallow root system. Before planting, amend the area with aged compost or well-rotted manure to improve fertility and soil structure. Choy Sum prefers a slightly acidic to neutral soil pH, with an ideal range of 6.0 to 7.0.
The plant grows best in full sun, requiring at least six hours of direct sunlight daily. However, it tolerates partial shade, which is beneficial in warmer climates. Siting the crop in a location that receives afternoon shade helps to maintain cooler soil temperatures, offering a way to delay bolting in the spring and extend the harvesting window. Proper site preparation minimizes stress and encourages robust vegetative growth.
Sowing Seeds and Thinning
Choy Sum seeds should be sown shallowly, ideally at a depth of about 1/4 inch (6mm), directly into the prepared garden bed. The seeds germinate quickly, typically emerging within three to seven days when soil temperatures are within the preferred range. For a continuous supply of fresh greens, succession planting is recommended.
Start a new row of seeds every two to three weeks until the weather becomes too warm for the crop. Initially, sow the seeds closely together, then thin the seedlings once they have developed their first set of true leaves. Thinning prevents overcrowding, which leads to stunted growth and encourages premature bolting due to resource competition.
The final spacing between plants should be approximately six to eight inches (15-20 cm) apart, allowing each plant room to develop a substantial rosette of leaves and a thick, harvestable stem. Rows should be spaced about 12 to 18 inches apart to permit good air circulation and allow for easy access when weeding and harvesting. Removing the thinned seedlings gently ensures the roots of the remaining plants are not disturbed.
Routine Care and Pest Control
Consistent moisture is important for maintaining a healthy Choy Sum crop and preventing the stress that triggers bolting. Because of their shallow roots, the plants require regular, shallow watering to keep the soil consistently moist but never waterlogged. Monitoring the soil and watering deeply once or twice a week, or more frequently in dry conditions, is sufficient.
A light, balanced feeding with a nitrogen-rich fertilizer should be applied every few weeks throughout the growing period to support the production of tender, leafy growth. Choy Sum is vulnerable to nitrogen deficiency, so incorporating a liquid feed or granular fertilizer with a higher first number (for nitrogen) every three to four weeks provides the necessary boost. Avoid excessive fertilization, which leads to soft, overly succulent growth that is more susceptible to pests.
As a member of the Brassica family, Choy Sum is a target for several common garden pests. Flea beetles, which chew small holes in the leaves, and cabbage worms (the larvae of the cabbage white butterfly) are common threats. Inspecting the undersides of leaves for the small, white or yellow eggs and handpicking any visible larvae is an effective organic control method.
Aphids cluster on the tender new growth, sucking the plant sap and potentially stunting the plant. A strong jet of water can dislodge aphids, or a treatment of insecticidal soap or neem oil can manage heavier infestations. For flea beetle and cabbage moth prevention, installing lightweight row covers immediately after planting creates a physical barrier, which is a reliable method for protecting young seedlings.
Harvesting the Crop
The moment of harvest is determined by the plant’s flowering stage, as the goal is to capture the stems at their most tender point. Choy Sum is ready for harvest about 30 to 50 days after sowing. This occurs when the central flower stalk is well-developed but the small, yellow buds have not yet opened. Harvesting before the flowers bloom ensures the sweetest, most succulent stem texture.
One common method is to cut the entire plant at the base, just above the soil line, using a sharp knife. This provides a single, large bunch of greens and is typically used for the final harvest. Alternatively, the “cut-and-come-again” method involves harvesting the outer leaves and stalks while leaving the central growing point intact.
This technique allows the plant to continue producing new shoots for an extended period, maximizing the yield. After harvesting, the greens should be stored unwashed in a breathable bag in the refrigerator, where they will maintain freshness for up to a week.