Vegetable · Flowering brassica
Choy Sum
Brassica rapa var. parachinensisA quick-growing Cantonese green harvested for its slender flowering stems rather than a head or root. Long, warm days push it to bloom fast, so it suits a short, cool-season window better than a slow summer crop. The one rule: cut stems while the buds are still closed for the sweetest, most tender bite.
Sow depth
¼ in
Spacing
6 in · rows 12 in
Sun
Sun or part shade
Germination
4–7 days
Time to harvest
35–50 days
Difficulty
Easy
When to sow choy sum
- Sow from about 4 weeks before your last expected frost until around your last expected frost.
- Sow from about 9 weeks before the first expected autumn frost until about 5 weeks before the first expected autumn frost.
Direct sow shallowly into moist, fertile soil once the coldest weather has passed.Sow little and often — every two to three weeks — for a steady harvest.Cover lightly and keep the seedbed damp until seedlings emerge.
Thin to 6 in so stems can bulk up rather than crowd each other thin.Water regularly; dry spells push plants to flower ahead of schedule.Weed while young — shallow roots dislike competition and disturbance.
Cut whole flowering stems 2–3 in from the base once buds are visible but unopened.Harvest the main stem first, then keep picking side shoots as they follow.Use promptly — flavor turns tough and bitter within a day or two of full bloom.
Companion plants
Alliums like garlic and onions planted nearby help mask choy sum from egg-laying cabbage pests.
Watch out for
Aphids — Cluster on tender stems and flower buds in mild weather. Rinse off with a strong water jet or invite ladybirds in.Flea beetles — Riddle leaves with small holes in warm, dry spells. Cover young plants with fine mesh from sowing.