How to grow choy sum
Overview
Choy sum (Brassica rapa var. parachinensis) is a fast-growing Asian green cultivated for its tender flowering stems and leaves. It is typically harvested just before the flowers open, yielding crisp, mildly sweet stems. Key to success is cool weather and consistent moisture.
Varieties
- Green Stem Choy Sum — Classic variety with pale green stems and dark green leaves, quick to mature in 30–45 days.
- White Stem Choy Sum — Similar to green stem but with white, more tender stalks; popular for stir-fries.
Soil Preparation
Choy sum prefers well-drained, fertile loam with pH 6.0–7.0. Enrich soil with well-rotted compost or aged manure before planting. Avoid heavy clay or waterlogged sites.
Growing Guide
Sow direct or transplant seedlings in full sun. Prepare rich, well-drained soil with pH 6–7, and space plants 20–30 cm apart. Water regularly to keep soil evenly moist, and apply a balanced liquid fertiliser every 2–3 weeks. Harvest stems before flowers fully open to maintain tenderness.
Sowing
Direct sow seeds 5 mm deep and 20 cm apart, thinning to 20–30 cm. Germination takes 5–10 days at 15–25°C. Can also be transplanted; harden off seedlings first.
Care
Feed every 2–3 weeks with a balanced liquid fertiliser during active growth. Remove yellowing lower leaves to improve air circulation. No pruning is needed; simply harvest stems as they mature.
Companion Planting
Good companions include carrots, onions, beets, lettuce, and peas. Avoid planting after other brassicas (broccoli, cabbage, kale) to prevent soilborne disease buildup.
Common Pests & Risks
Cabbage white caterpillars can defoliate plants; cover with fine netting or apply Bacillus thuringiensis. Aphids and flea beetles are also common; control with neem oil, insecticidal soap, or introduction of beneficial insects like ladybirds.
Harvesting
Harvest choy sum when stems reach 20–30 cm tall, just before the flower buds open fully. Cut the main stem at the base to encourage side shoots for a second harvest. Use immediately for best flavour.
In the Kitchen
Use whole young stems and leaves in stir-fries, soups, or blanched as a side dish. Store in a plastic bag in the fridge for up to 5 days. Best eaten fresh for crisp texture.
Troubleshooting
Premature bolting: caused by heat or dry soil; plant in cool season and keep moisture steady. Yellow leaves: often from overwatering or poor drainage; ease watering and improve soil. Stunted growth: check soil pH; adjust to 6–7. Holes in leaves: cabbage white caterpillars; use netting. Sticky residue: aphids; spray with neem oil or introduce ladybirds.