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Comprehensive Temperature Requirements by Growth Stage for Carrot
Overview
This report organizes temperature requirements for each major growth stage of carrot (Daucus carota L.) using parameters: optimal_min, optimal_max, base_temperature, low_stress_threshold, high_stress_threshold, max_temperature, frost_threshold, and sterility_risk_threshold (flowering only). It is based on domestic and international scientific and technical primary sources and agricultural guidelines. Values with unclear or conflicting research are noted explicitly.
Parameter Definitions
optimal_min / optimal_max
Temperature range at which growth and physiological function proceed most favorably at that stage.base_temperature Minimum temperature at which germination and growth nearly stop; also used as the basis for GDD calculation.
low_stress_threshold / high_stress_threshold
Temperature below (or above) which growth and quality decline or injury becomes likely.max_temperature Upper limit at which growth/germination stops or physiological injury/death may occur.
frost_threshold Air temperature at which tissue freezes and cellular injury or death is likely.
sterility_risk_threshold Temperature at which reproductive cell function is impaired during flowering/pollination/fertilization, sharply increasing sterility (less detailed research for carrot than cereals).
Temperature Parameters by Growth Stage (Summary Table)
| Growth Stage | optimal_min | optimal_max | base_temperature | low_stress_threshold | high_stress_threshold | max_temperature | frost_threshold | sterility_risk_threshold (flowering only) | References |
|---|---|---|---|---|---|---|---|---|---|
| Germination | 15°C | 25°C | 5–6°C | Below 10°C: delay | Above 25°C: decline / above 34–35°C: no germination | 35°C (no germination) | −2 to −3°C (seedling death) | — | [1][2][3][4][5][6][7][8] |
| Leaf/stem elongation, vegetative growth | 18°C | 21–22°C | ~3°C | Below 10°C: slow growth, etiolation | Above 23–28°C: deformity, poor color / above 28°C: stop | 28–35°C (growth/enlargement stop) | 0 to −2°C (aboveground death) | — | [2][3][5][6][7][8] |
| Root enlargement | 16°C | 21°C | ~3°C | Below 10°C: poor swelling | Above 21°C: color disorder / above 23–28°C: quality decline | 28–35°C (growth stop, injury) | 0 to −2°C (ground-level death) | — | [2][3][5][6][7][8] |
| Flowering / bolting | 15–25°C | 21°C | — (vernalization requires below 10°C) | Low temp: flower bud differentiation/bolting induction | — (estimated functional decline above 28–30°C) | Usually above 35°C (reproductive organ injury) | Below 0°C (flower injury) | — (detailed indicators mainly for cereals) | [2][3][5][6][8][9] |
Stage-by-Stage Explanation and Value Details
1. Germination (Sowing to Emergence)
- Optimal temperature: 15–25°C for shortest and best germination rate. About 20 days to germination at 11°C; more than 30 days at 8°C [5][6][7][8].
- Base temperature: 5–6°C is minimum for germination; physiological activity nearly stops below this.
- Low-temperature stress: Below 10°C, growth delay and reduced germination rate; marked delay below 8°C [5][8].
- High-temperature stress / max temperature: Germination rate decreases above 25°C; disorders above 30°C; no germination above 35°C [2][4][8].
- Frost temperature: Lethal death of seedlings immediately after germination below −2 to −3°C [7][8].
2. Vegetative Growth (Leaf and Stem Elongation)
- Optimal temperature: 18–21/22°C [3][7].
- Base temperature: About 3°C; growth markedly slows below this [3][5][7].
- Low-temperature stress: Below 10°C, leaves become thin, pale, and prone to etiolation [3][7].
- High-temperature stress: Above 23–28°C, root color and shape deteriorate; growth stops and roots become prone to splitting above 28°C [5][7][8].
- Max temperature: Growth stop or death around 28–35°C [3][7].
- Frost temperature: Frost on aboveground parts and leaves at 0 to −2°C [7].
3. Root Enlargement and Quality Formation
- Optimal temperature: 16–21°C is best for root enlargement and color; quality declines above 21°C [3][7][8].
- Base temperature: About 3°C (growth continues); low-temperature stress below 10°C causes poor root thickening.
- High-temperature stress: Quality decline above 21°C; rapid enlargement and color disorders above 23–28°C; nearly stops above 28°C [5][7][8].
- Max temperature / frost temperature: As above.
4. Flowering / Bolting (After Vernalization)
- Optimal temperature: 15–25°C (flower bud formation to flowering) [3][6].
- Base temperature: No direct description; bolting requires seedling vernalization below 10°C (around 5–7°C) for 1–2 months to promote flower bud differentiation [6][8][9].
- High-temperature stress: No clear threshold stated; reproductive organ development disorder or pollination failure estimated above 28–30°C (less organized than for cereals) [6][9].
- Max temperature: Risk of reproductive organ development/function disorder above ~35°C, but no explicit Japanese agricultural guideline [2][9].
- Frost temperature: Flower damage below 0°C.
- Sterility threshold: sterility_risk_threshold (high-temperature sterility) is hardly defined for carrot in Japanese or international literature; precise definitions exist mainly for rice and other cereals (above 34–35°C) [10].
Literature Variation and Undefined Parameters
- Major parameters such as optimal and base temperature are largely consistent across domestic (JA/MAFF, agricultural cooperatives, extension) and overseas literature.
- Germination is most temperature-sensitive; minor variation occurs by seed cultivar and soil conditions, but 15–25°C is generally best; extreme low and high temperatures are main causes of injury [5][6][8].
- High-temperature sterility temperature during flowering is well defined for rice, wheat, and other cereals including cultivar differences, but no Japanese or English literature explicitly states equivalent thresholds for carrot (research centers on bolting and flower bud differentiation temperature treatment).
- Extreme high temperature may adversely affect flowering, pollination, and seed formation, but descriptions such as "sterility sharply increases above 35°C" are not found [9][10].
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Conclusion
Each growth stage from carrot germination to flowering proceeds most smoothly in different temperature ranges. Germination is most sensitive; outside the optimal range, serious germination rate decline occurs. Vegetative growth and root enlargement are ideal around 16–21°C; deviation leads to quality deterioration, malformed roots, and growth disorders.
For flowering, vernalization (low-temperature induction) for bolting and flower bud formation is important; specific thresholds for high-temperature injury and sterility are not stated for carrot. No "flowering high-temperature tolerant cultivars" like those for cereals exist for carrot. This is common to all domestic and international guidelines and academic papers.
Sources
[1] Carrot cultivation methods and growing tips | Takii Net Shop: https://shop.takii.co.jp/selection/ninjin2011.html
[2] Carrot cultivation guidelines - JA Iga Furusato: https://www.jaiga.or.jp/?p=682
[3] Toward a low-carbon society "Japan's experience, Asia's challenge": http://2050.nies.go.jp/sympo/090212/ws/file/report_20090213_S-3WS.pdf
[4] Carrot Seed Germination at High Temperature: Effect of Genotype: https://journals.ashs.org/view/journals/hortsci/43/5/article-p1538.xml
[5] Carrot cultivation: https://www.hidefmc.com/ninjin/
[6] Why doesn't carrot germinate? Causes and how to improve germination: https://nogyoya.jp/fc/column/konsai/qzvwfd9k8alj/
[7] Summer-sown carrot cultivation manual (quality and yield improvement) - MAFF: https://www.maff.go.jp/j/seisan/gizyutu/hukyu/h_zirei/brand/attach/pdf/201023_3-42.pdf
[8] Improving carrot germination rate: https://www.pref.kagoshima.jp/al08/chiiki/nansatsu/sangyo/nougyou/gijutsu/documents/62039_20171005192314-1.pdf
[9] Vernalization Requirement, but Not Post-Vernalization Day Length Conditions Flowering in Carrot Daucus carota L: https://www.researchgate.net/publication/360044672_Vernalization_Requirement_but_Not_Post-Vernalization_Day_Length_Conditions_Flowering_in_Carrot_Daucus_carota_L
[10] Cultivar differences in rice sterility due to high temperature during flowering - Saitama Prefecture: https://www.pref.saitama.lg.jp/documents/32295/01_suitouyuuseihunenn.pdf