Pak Choi Nutrient, pH & EC Guide for Hydroponics
Baby pak choi at EC 1.5–1.8 produces uniformly tender leaves and stems - higher EC thickens and toughens leaf texture, making EC choice a direct quality lever for restaurant buyers.
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Pak choi is closely related to bok choy and shares its brassica nutritional profile, but is distinguished by a wider petiole and more deeply savoy-textured leaves in many varieties. It is one of the most versatile hydroponic crops, producing high-quality baby greens for salad mixes at 25–30 days or full-size heads at 45–55 days. EC management has a direct and predictable effect on leaf and stem texture, making it a deliberate quality tool rather than just a growth parameter.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Seedling | 6.0–7.0 | 0.8–1.2 | 400–600 | Fast germination at 15–22°C; 5–7 days to emergence | | Baby (harvest at 25–30 days) | 6.0–7.0 | 1.5–1.8 | 750–900 | Hold throughout for tender uniform texture throughout leaf and stem | | Full-size (harvest at 45–55 days) | 6.0–7.0 | 2.0–2.5 | 1000–1250 | Higher EC produces firmer, slightly thicker tissue in full-size heads |
Note on PPM: Values above use a 500 conversion factor (EC × 500 = PPM). Some meters use 700 - multiply by 1.4 to convert.
Key Nutrients
| Nutrient | Role in This Plant | Deficiency Sign | Correction | |----------|-------------------|-----------------|------------| | Calcium | High demand; tip burn prevention critical in inner leaves; Ca:Mg ratio 3:1 for brassica family | Brown papery tip burn on inner leaves; distorted young growth | Maintain Ca at 150–200 ppm; Ca:Mg ratio 3:1; add fan before raising Ca concentration | | Sulfur | Glucosinolate synthesis for characteristic mild brassica flavour | Uniform yellowing of youngest leaves; loss of mild peppery character | Maintain SO4 at 40–60 ppm via MgSO4 or potassium sulfate | | Boron | Cell-wall integrity in rapidly expanding brassica leaves; trace element critical | Distorted, thickened, or hollow inner leaf or stem tissue | Keep B at 0.2–0.5 ppm; add carefully as toxicity occurs above 1–2 ppm |
Deficiency Identification
- Tip burn on inner leaves: Transpiration-limited calcium transport. Add a small oscillating fan directed at the canopy. This is the most effective single intervention for brassica tip burn.
- Tough, leathery texture in baby pak choi: EC above 1.8 during early production. Lower EC to 1.5–1.8 for baby-leaf harvest. Texture does not recover after toughening.
- Distorted inner leaf tissue: Boron deficiency. Supplement B at 0.2–0.4 ppm very carefully.
- Uniform young-leaf yellowing: Sulfur deficiency. Supplement MgSO4 to restore sulfur and magnesium simultaneously.
Feeding Schedule Notes
Pak choi offers two distinct production strategies. For baby pak choi targeted at high-end salad mix or restaurant garnish: maintain EC at 1.5–1.8 throughout and harvest at 25–30 days for maximum tenderness. For full-size heads: ramp from 0.8–1.2 at seedling to 2.0–2.5 at maturity over 45–55 days. The texture difference between these EC ranges is measurable and intentional. Ensure a small fan runs continuously over the crop from day one to prevent tip burn via improved transpiration. Maintain solution temperature between 15–22°C. Full reservoir changes every 7–10 days.
Research note: Baby pak choi at EC 1.5–1.8 produces uniformly tender leaves and stems; leaves and stems toughen at higher EC. EC choice is a direct quality lever for texture consistency.