Microgreens Nutrient, pH & EC Guide for Hydroponics
Microgreens draw most of their nutrition from seed stores, making solution EC less important than harvest timing - nutrients drop sharply once cotyledons yellow after day 12–14.
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Microgreens are a unique hydroponic category where seed nutrient stores supply the majority of nutrition through the cotyledon stage - external solution EC is far less critical than for any mature crop. The primary grower variables that affect nutritional quality are harvest timing relative to cotyledon development and light exposure after blackout. Understanding that peak nutrition occurs at the cotyledon stage before true-leaf emergence is the single most important insight for microgreen production.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Germination (blackout) | 5.5–6.5 | 0.0–0.5 | 0–250 | Plain water or very dilute solution; seed stores supply all required nutrition | | Cotyledon stage | 5.5–6.5 | 0.8–1.2 | 400–600 | Light solution supports cotyledon expansion; harvest window begins here | | Extended grow (if applicable) | 5.5–6.5 | 1.0–1.4 | 500–700 | Only if growing to first true-leaf stage; nutritional density decreasing from this point |
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 | |----------|-------------------|-----------------|------------| | Beta-carotene | Highest in sunflower, pea, and broccoli microgreens at cotyledon stage; light-exposure dependent | Yellowing or pale cotyledons indicate declining carotenoids post-peak | Harvest before cotyledons yellow; ensure adequate light (150–250 µmol) after blackout period | | Vitamin C | Peaks at cotyledon stage in most species before true leaves emerge | Measured by harvest timing, not visible sign | Harvest at cotyledon fully open, before first true-leaf tip appears | | Folate | Concentrated particularly in legume microgreens (pea, sunflower) | Not visibly detectable | Ensure correct species selection; legume types are highest folate sources |
Deficiency Identification
- Yellowing cotyledons before day 10–12: Insufficient light after removing blackout cover, or seed quality issue. Increase light to 150–250 µmol PPFD immediately after uncovering.
- Leggy, pale, stretched stems: Insufficient light during post-blackout growth. Reduce distance from light source or increase intensity.
- Damping off (stem collapse at soil line): Overwatering and poor air circulation. Bottom-water only; ensure grow mat is moist not saturated; add small fan for airflow.
- Uneven germination: Inadequate seed contact with medium, uneven weight during blackout, or poor seed lot. Press seeds firmly into moistened medium; apply even weight during blackout.
Feeding Schedule Notes
Most microgreens require no nutrient solution at all during germination - plain water moistening the growing medium is sufficient, as seed stores contain all required nutrition for the first 7–10 days. After the blackout period (typically 3–5 days for most species), introduce light and begin bottom-watering with a dilute solution at EC 0.8–1.2. Harvest timing is the dominant quality variable: harvest at or just after cotyledon fully opens for peak Vitamin C and carotenoids. Species-specific cycles range from 5–7 days (radish, mustard) to 10–14 days (sunflower, peas). Do not hold microgreens past the point when cotyledons begin to pale or the first true leaves emerge - nutritional density declines from this point.
Research note: USDA ARS analyses found radish and broccoli microgreens contain 10–40x higher Vitamin C, E, and beta-carotene than mature counterparts; this ratio drops if cotyledons yellow after day 12–14.