Choy sum
Brassica rapa var. parachinensis
Also known asYu choy · Chinese flowering cabbage · Caisin · Cai xin · Flowering Chinese cabbage
Environment
The bounded range this crop tolerates.
Climate and zones
- USDA zones
- 5–10 (winter low around -29°C)
- Frost
- tolerates light frost
- Season
- cool (spring/fall)
Growing systems
Root mass: light.
Growing media
| Medium | pH effect | Retention | Bacterial surface |
|---|---|---|---|
| Rockwool (Mineral wool) | alkaline until pre-soaked | very high | low |
| Expanded clay pebbles (LECA) | neutral / inert | low | high |
| Coco coir (Coconut coir) | slightly acidic | high | moderate |
| Net pot, no medium (Bare-root) | - | - | - |
| Soil-based mix (Potting soil) | varies | high | high |
Nutrient demand by stage
NPK ratios are relative weights. EC targets shift through the plant's life.
| Stage | N | P | K | EC (mS/cm) |
|---|---|---|---|---|
| seedling | 1 | 1 | 1 | 0.7 |
| vegetative | 3 | 1 | 2 | 1.8 |
Companion-growing notes
- Heavy uptake of calcium. Co-grown crops with the same demand will end up deficient even at "correct" EC.
Aquaponics suitability
Compatible
Fish waste provides enough nitrogen for healthy growth. Supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.
Care notes
One of the fastest and easiest Asian greens for hydroponic production. EC 1.2-2.0 mS/cm. pH 5.5-6.8. Temperature: 15–25°C (cool to moderate; bolts in sustained heat above 28°C, but unlike lettuce, the flowers are part of the harvest so early bolting is less problematic). Moderate light (DLI 12-18 mol/m2/day). From seed to harvest: 4-6 weeks, making it one of the fastest brassica crops. NFT, DWC, raft, and vertical systems all work. Harvest the whole plant or cut the main stem and allow side shoots to develop for a second harvest. The speed and ease make choy sum ideal for commercial hydroponic operations targeting Asian vegetable markets. Succession plant every 2-3 weeks for continuous supply. Nutrient demand is moderate; standard leafy green formulation. Flea beetles and caterpillars are potential pests in open greenhouses. For hydroponic growers near Asian communities, choy sum is a high-demand, fast-turnover crop with consistent market pricing ($4-8/kg). In aquaponics, choy sum grows vigorously in warm, nutrient-rich water.