Choy sum Brassica rapa var. parachinensis
Choy sum (Brassica rapa var. parachinensis) is an annual vegetable in the Brassicaceae family, native to Southern China (cultivar group of Brassica rapa). It grows 30–45 cm (12–18 in) tall and 20–30 cm (8–12 in) wide, wants full sun and moderate water, and is hardy to about -3 °C (27 °F). Space plants about 15 cm (6 in) apart.
Plan Choy sum in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Choy sum at a glance
| Type | Annual vegetable |
|---|---|
| Family | Brassicaceae |
| Mature height | 30–45 cm (12–18 in) |
| Mature spread | 20–30 cm (8–12 in) |
| Spacing | 15 cm (6 in) centre to centre |
| Sun | Full sun, at least 5 h of direct sun a day |
| Water | Moderate; drought tolerance none, waterlogging tolerance low |
| Soil pH | 6–7 |
| Cold hardiness | About -3 °C (27 °F) once established (roughly USDA zone 9) |
| Heat stress | Likely above about 30 °C (86 °F) |
| Flowering | about 6–9 weeks after planting, for 3–5 weeks |
| Days to maturity | About 45 days from planting |
| Wind tolerance | Low |
| Pollinator value | Moderate |
| Edible | Yes: flower stalks, leaves, flower buds |
| Native to | Southern China (cultivar group of Brassica rapa) |
| Common in gardens of | 🇨🇳 China, 🇸🇬 Singapore, 🇹🇭 Thailand |
Is Choy sum toxic?
- People: not known to be toxic
- Cats: not known to be toxic
- Dogs: not known to be toxic
Not toxic; raw brassicas can cause gas in pets if eaten in quantity.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Choy sum
Good neighbours
- good With Rhubarb: Traditional lore says rhubarb planted near brassicas helps against clubroot and pests; the evidence is weak and not confirmed by trials. Evidence D
- good With Nasturtium: Nasturtiums act as a trap crop for cabbage white butterflies and blackfly, drawing some pressure away from brassicas. Evidence C
Shared pests and diseases
- Clubroot: Clubroot spores persist in soil up to 20 years; keep brassicas in a rotation. Evidence B
Questions about Choy sum
- How far apart should I plant Choy sum?
- About 15 cm (6 in) apart, centre to centre. A mature plant spreads 20–30 cm (8–12 in).
- Does Choy sum need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does Choy sum need?
- Moderate water. Drought tolerance is none and waterlogging tolerance low.
- How cold-hardy is Choy sum?
- It tolerates about -3 °C (27 °F) once established, roughly USDA zone 9. As an annual it is usually planted out after the last frost.
- When does Choy sum flower?
- About 6–9 weeks after planting, for 3–5 weeks.
- Is Choy sum poisonous to cats and dogs?
- For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Not toxic; raw brassicas can cause gas in pets if eaten in quantity.
- What grows well with Choy sum?
- Traditional lore says rhubarb planted near brassicas helps against clubroot and pests; the evidence is weak and not confirmed by trials. Nasturtiums act as a trap crop for cabbage white butterflies and blackfly, drawing some pressure away from brassicas.
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- EcoCrop crop environmental requirements, FAO
- University extension gardening guides (general), Various land-grant university extensions
- Flora & Fauna Web, National Parks Board, Singapore
Notes and assumptions
- Harvested at first flower; quick crop of about 40-55 days in warm weather.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Broccoli Brassica oleracea var. italica
- Cauliflower Brassica oleracea var. botrytis
- Cabbage Brassica oleracea var. capitata
- Kale Brassica oleracea var. sabellica
- Radish Raphanus sativus
- Bok choy Brassica rapa subsp. chinensis
- Brussels sprout Brassica oleracea var. gemmifera
- Kohlrabi Brassica oleracea var. gongylodes