Spinach Nutrient, pH & EC Guide for Hydroponics
Spinach tolerates and performs well at higher EC than most salad greens, but elevated EC also increases oxalate accumulation - baby-leaf harvest at 25–30 days keeps oxalates significantly lower.
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Spinach is one of the more nutrient-tolerant leafy greens and can handle EC levels that would stress lettuce, but this comes with a trade-off: higher EC and longer grow times both increase oxalic acid accumulation in leaves. Growers targeting lower-oxalate product for health-conscious consumers should harvest young and manage EC at the lower end of the range. Spinach also prefers cooler solution temperatures than most hydroponic crops.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Seedling | 6.0–7.0 | 1.0–1.4 | 500–700 | Tolerates higher starting EC than lettuce; cool water (15–18°C) improves germination | | Vegetative | 6.0–7.0 | 1.8–2.0 | 900–1000 | Ramp gradually; target pH 6.5 as optimal centre for iron and manganese availability | | Mature | 6.0–7.0 | 2.0–2.3 | 1000–1150 | Monitor oxalate trade-off; lower for baby-leaf harvest |
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 | |----------|-------------------|-----------------|------------| | Iron (chelated) | Essential for chlorophyll synthesis in dark-green spinach leaves | Yellowing of youngest leaves, veins stay green | Use Fe-EDTA; maintain pH 6.0–6.5 for best iron availability in this pH range | | Manganese | Works alongside iron for chlorophyll production; spinach has elevated Mn demand | Interveinal yellowing on young leaves, similar to Fe deficiency | Ensure Mn at 0.5–1.0 ppm; distinguish from Fe deficiency by checking pH first | | Nitrate nitrogen | Primary nitrogen form; spinach actively concentrates dietary nitrate in leaf tissue | Overall pale colour, thin leaves, slow growth | Maintain NO3-N at 150–200 ppm; note this also increases leaf nitrate content |
Deficiency Identification
- Young-leaf chlorosis: Iron or manganese deficiency, both common in spinach when pH drifts above 6.8. Check and adjust pH before adding chelated minerals.
- Overall pale green with thin leaves: Nitrogen deficiency. Increase EC by 0.3–0.5 mS/cm and confirm NO3-N is the primary nitrogen source.
- Leaf edge burn with older-leaf necrosis: Potassium deficiency or accumulated salt stress. Perform a full reservoir change and check individual ion concentrations.
- Slow growth in otherwise healthy plants: Confirm water temperature is not above 22°C. Spinach slows noticeably above this threshold and may bolt above 25°C.
Feeding Schedule Notes
Spinach germinates and grows best at solution temperatures between 15–20°C - warmer than this slows growth and promotes bolting. Start at EC 1.0–1.4 for the first 10–14 days, then step up to 1.8–2.0. For baby-leaf production targeting harvest at 25–30 days, hold EC at 1.2–1.6 throughout; for full-size mature leaves targeting 40–50 days, ramp to 2.0–2.3 in the final 10 days. Maintain pH between 6.0–7.0 with 6.5 as the sweet spot for iron-manganese availability. Full reservoir changes every 7–10 days prevent nitrate-to-ammonium ratio drift.
Research note: At EC 2.0–2.3, spinach accumulates higher oxalates than at EC 1.2–1.6; baby-leaf harvest at 25–30 days has measurably lower oxalate content than mature harvest.