Stevia Nutrient, pH & EC Guide for Hydroponics
Rebaudioside-A content peaks 2–4 weeks before first flower opens in stevia - once flowers open, glycoside concentration drops sharply as the plant redirects resources to seed production.
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Stevia is one of the most unusual hydroponic crops in terms of what is being optimised: the goal is not biomass or essential oil, but steviol glycoside content - compounds 200–300 times sweeter than sucrose by weight. Like many secondary metabolites, glycoside concentration peaks at a specific developmental window relative to flowering, and then declines sharply. Nutrient management is secondary to harvest timing and variety selection for this crop.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Seedling | 6.0–7.0 | 0.4–0.6 | 200–300 | Very low starting EC; stevia adapted to low-fertility tropical/subtropical soils | | Vegetative | 6.0–7.0 | 0.8–1.0 | 400–500 | Modest EC; avoid high nitrogen which dilutes glycoside concentration | | Pre-harvest | 6.0–7.0 | 0.8–1.4 | 400–700 | Harvest 2–4 weeks before first flower opens for peak Reb-A content |
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 | |----------|-------------------|-----------------|------------| | Potassium | Modest support for steviol glycoside biosynthesis; adequate at EC 0.8+ | Reduced glycoside content; marginal leaf scorch | Maintain K at 100–150 ppm; does not need the high K demand of fruiting crops | | Nitrogen (low) | Excess N dilutes steviol glycoside concentration in leaves; keep at lower bound | Rapid, large-leafed growth with reduced sweetness indicates excess N | Target N at 60–80 ppm NO3-N; this is deliberately low; resist increasing EC to speed growth | | General mineral balance (low) | Balanced dilute solution; stevia is adapted to low-fertility Paraguay highland soils | True deficiency unlikely at EC 0.8–1.4 | Use standard formula at 40–50% of lettuce rate |
Deficiency Identification
- Reduced leaf sweetness (tasteless or mildly sweet): Either harvest timing is wrong (too late, past flowering) or excess nitrogen has diluted glycoside content. Check both before adjusting nutrients.
- Yellowing from oldest leaves upward: Nitrogen deficiency at very low EC. Increase EC slightly to 1.0–1.2 while keeping N conservative.
- Bolting (flower stem elongation): Stevia is a short-day plant; flowering is triggered by days shorter than 13 hours. Use a 14–16 hour photoperiod to delay flowering and extend the vegetative harvest window.
- Slow germination: Stevia seed germination is notoriously poor and variable; establish from tissue-culture plantlets or cuttings of certified Reb-A dominant varieties for reliable production.
Feeding Schedule Notes
Stevia is best established from tissue-culture plantlets or rooted cuttings from a certified high-Reb-A variety - germination from seed is unreliable and the resulting plants have variable glycoside profiles. Root cuttings at EC 0.4–0.6 before stepping up to 0.8–1.0. Maintain a 14–16 hour photoperiod throughout to delay flowering and extend the high-glycoside vegetative phase. Monitor plants weekly for the first appearance of flower buds. The optimal harvest window is 2–4 weeks before the first flower opens - this is when Reb-A content peaks. Once flowers open, glycoside concentration drops sharply and does not recover. Cut plants above the lowest 2–3 nodes to allow regrowth for successive harvests. Solution temperature at 20–26°C.
Research note: Rebaudioside-A content (200–300x sweeter than sucrose) peaks 2–4 weeks before first flower opens. Once flowers open, glycoside concentration drops sharply as plant redirects to seed production.