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Spinach (Spinacia oleracea) — Temperature Requirements by Growth Stage
Overview
Spinach (Spinacia oleracea) is a cool-season leafy crop whose growth and quality depend strongly on stage-specific temperature. Optimal temperature management from germination through vegetative growth and bolting is essential for stable production and high-quality harvest. Based on Japanese public agencies and seed company manuals and academic sources, this report organizes temperature parameters (optimal_min, optimal_max, base_temperature, low_stress_threshold, high_stress_threshold, max_temperature, frost_threshold, sterility_risk_threshold) by stage.
Temperature Requirements by Growth Stage
1. Germination
- optimal_min / optimal_max: 15–20°C
- base_temperature: Not stated (4°C often used as practical minimum for germination)
- low_stress_threshold: No clear numeric data
- high_stress_threshold: Germination rate drops markedly above 25°C; nearly impossible at 35°C
- max_temperature: 35°C maximum for germination
- frost_threshold: Germination possible around 4°C but slower at low temperature
Key points: Risk of poor germination at both low and high temperature; germination possible between 4°C and 25°C; above 25°C, rate falls sharply and damping-off risk increases.
2. Vegetative Growth
- optimal_min / optimal_max: 10–20°C (some sources emphasize 15–20°C by cultivar)
- base_temperature: Not stated
- low_stress_threshold: No clear numeric data (pH below 5.5 causes growth disorders; no temperature value stated)
- high_stress_threshold: Above 25°C—growth suppression, quality decline, more disease
- max_temperature: 25°C and above sharply limits growth
- frost_threshold: Cold hardy to about −10°C; survives winter field production
Key points: Exceeding optimal range promotes early bolting and disease; among leafy crops, spinach has exceptional cold tolerance.
3. Flowering / Bolting
- optimal_min / optimal_max: Not stated (bolting promoted when vegetative optimum 10–20°C is exceeded)
- high_stress_threshold: Above 25°C, bolting risk rises (especially under long days)
- max_temperature: 25°C and above suppresses growth and promotes bolting
- sterility_risk_threshold: No official numeric data for pollen sterility
Key points: Long days (13+ hours) combined with high temperature (25°C+) accelerate bolting; no clear domestic sterility temperature data (spinach is mainly a leaf crop, not seed production).
Cultivation Notes
- Soil pH and disease: Below pH 5.5 harms germination and growth; powdery mildew and downy mildew risk high at 8–18°C with high humidity.
- Management: Uniform sowing, timely thinning, harvest before 22–25 cm plant height for quality.
- Temperature: Summer production in cool highlands; winter production possible without heating in cold regions.
Data Gaps
- Clear numeric values for base_temperature, low_stress_threshold, and sterility_risk_threshold are not found in major Japanese public/academic sources; flowering pollen sterility data are scarce because spinach is mainly grown for leaves.
Temperature Requirements Summary Table
| Stage | optimal_min | optimal_max | base_temperature | low_stress_threshold | high_stress_threshold | max_temperature | frost_threshold | sterility_risk_threshold |
|---|---|---|---|---|---|---|---|---|
| Germination | 15°C | 20°C | ~4°C | No data | 25°C | 35°C | 4°C | — |
| Vegetative | 10°C | 20°C | No data | No data | 25°C | 25°C | −10°C | — |
| Bolting / flowering | Not stated | Not stated | No data | No data | 25°C | 25°C | Not stated | No data |
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Conclusion
Successful spinach production requires appropriate temperature at each stage—especially germination and vegetative growth. Avoid heat stress above 25°C and extreme cold below −10°C; manage soil acidity and disease; adjust sowing and management by region and season. Parameters without numeric data need further research but are organized within current official manuals and studies.