Bok Choy Nutrient, pH & EC Guide for Hydroponics
Bok choy accumulates abundant calcium hydroponically yet still suffers tip burn - caused by low transpiration not low Ca - and a small oscillating fan resolves it without any nutrient change.
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Bok choy is a fast-maturing brassica that performs exceptionally well in hydroponic systems, reaching harvest in as little as 30–45 days. Its most common production challenge - inner-leaf tip burn - is frequently misattributed to calcium deficiency when the actual cause is reduced transpiration in enclosed grow spaces. Understanding this distinction prevents unnecessary nutrient adjustments and resolves the problem far more effectively.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Seedling | 6.0–7.0 | 0.8–1.2 | 400–600 | Germinates readily at 15–22°C; cool temperatures preferred over warm | | Vegetative | 6.0–7.0 | 1.5–2.0 | 750–1000 | Ramp steadily; boron and calcium important from this stage | | Mature | 6.0–7.0 | 2.0–2.5 | 1000–1250 | Full-size heads; baby bok choy can be harvested earlier at lower EC |
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 (Ca:Mg 3:1) | Cell-wall integrity in brassica leaves; Ca:Mg ratio critical for brassica family | Brown papery tip burn on inner leaves; hollow centres in severe cases | Maintain Ca at 150–200 ppm; Ca:Mg ratio should be approximately 3:1; add fan before adjusting Ca | | Boron | Cell-wall development and cross-linking in rapidly expanding brassica leaves; trace requirement | Distorted, thickened, or hollow inner leaf tissue | Keep B at 0.2–0.5 ppm; use boric acid or borax in small quantities | | Sulfur | Glucosinolate and characteristic brassica flavour compound synthesis | Uniform young-leaf yellowing; loss of mild peppery flavour | Maintain SO4 at 40–60 ppm via magnesium sulfate or potassium sulfate |
Deficiency Identification
- Inner-leaf tip burn with adequate Ca in solution: Transpiration-limited calcium transport. Add a small oscillating fan to improve air movement over the canopy. This single change resolves most bok choy tip burn without any nutrient adjustment.
- Distorted or hollow inner leaves: Boron deficiency. Increase B to 0.3–0.5 ppm carefully - boron toxicity occurs at only 1–2 ppm, so precision matters.
- Uniform young-leaf yellowing: Sulfur deficiency. Add MgSO4 to restore both sulfur and magnesium.
- Slow growth or purple stem colouring: Phosphorus deficiency, common in cooler solution (below 15°C). Increase temperature and check P at 40–60 ppm.
Feeding Schedule Notes
Bok choy is well-suited to both NFT and DWC systems. For baby bok choy (harvest at 15–20 cm), maintain EC at 1.5–1.8 throughout and harvest at 30–35 days from transplant. For full-size heads, ramp to 2.0–2.5 in weeks 4–6. The most impactful setup decision is airflow: place a small oscillating fan directed across the crop canopy from day one. This both prevents tip burn through improved transpiration and reduces fungal pressure in the humid brassica crown. Maintain solution temperature between 15–22°C. Full reservoir changes every 7–10 days prevent boron and trace element depletion.
Research note: Bok choy accumulates more Ca hydroponically than in soil, yet tip burn occurs from low transpiration, not low Ca - a small oscillating fan prevents it without any nutrient adjustment.