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Pumpkin (Cucurbita spp.) — Comprehensive Temperature Requirements by Growth Stage ​

Overview ​

Pumpkin (mainly Cucurbita moschata or C. maxima in Japan) requires appropriate temperature management at each stage from germination through maturation, harvest, and even storage. Temperature strongly influences physiology from germination and vegetative growth to flowering, pollination, fruit enlargement, quality, and storability. Drawing on Japanese agricultural guidance, literature, and reliable international horticultural guidelines, this report systematically summarizes the temperature ranges required at each growth stage and the associated parameters (optimal_min, optimal_max, base_temperature, low_stress_threshold, high_stress_threshold, max_temperature, frost_threshold, and—for flowering only—sterility_risk_threshold). Where values are unclear or Japanese domestic data are sparse, that is noted explicitly.

Temperature Parameters by Growth Stage ​

1. Germination Stage ​

  • optimal_min: 25°C
  • optimal_max: 30°C
  • base_temperature: 12–15°C
    • Minimum germination temperature is 12–15°C; below this, germination is extremely delayed or stops[6][15].
  • low_stress_threshold: Not clearly defined, but germination rate drops markedly below 20°C[6][15].
  • high_stress_threshold: 35°C (poor germination above 35°C)[6][15].
  • max_temperature: 40°C (no germination)[6][15].
  • frost_threshold: Extremely frost-sensitive; sowing and transplanting should occur only after frost risk has passed[6][9][12][15].
  • Notes: Below 15°C, germination is uneven and failure is common.

2. Seedling & Early Vegetative Stage ​

  • optimal_min: 20°C
  • optimal_max: 25°C
  • base_temperature: 12–15°C
  • low_stress_threshold: Below 15°C, growth stalls or is delayed[15].
  • high_stress_threshold: 30–35°C (etiolation and weak seedlings; exact figures not always stated)[6][8][10][15].
  • max_temperature: 35°C (increased risk of wilting and sunscald)[6][8].
  • frost_threshold: All green tissue is extremely frost-sensitive—exposure causes immediate death[6][8][10][13][14].
  • Notes: 20–25°C (day) / 15–18°C (night) is recommended for healthy transplants; seedlings have almost no cold hardiness.

3. Main Vegetative Growth Stage (True Leaf Expansion & Vine Elongation) ​

  • optimal_min: 18°C
  • optimal_max: 25°C
  • base_temperature: 10–12°C
  • low_stress_threshold: Below 15°C, leaf expansion is delayed and yellowing occurs[8][15].
  • high_stress_threshold: 30–35°C (leaf scorch, abnormal vine elongation, increased disease risk)[8][9][15].
  • max_temperature: 35°C
  • frost_threshold: Fatal to all green parts—no field work when frost is possible[6][8][9][10][12][13][14][15].

4. Flowering & Pollination Stage ​

  • optimal_min: 10°C
  • optimal_max: 30°C
  • base_temperature: 10°C
  • low_stress_threshold: Below 10°C, flowers fail to open and pollination is poor[2][3].
  • high_stress_threshold: Above 30°C, flower number and pollination efficiency decline[2][3][7].
  • max_temperature: 32°C (fruit set on female flowers deteriorates sharply above 32°C)[2][3].
  • frost_threshold: Flowers and young fruit are destroyed by frost[6][8][9][10][13][14][15].
  • sterility_risk_threshold: 32°C
    • Above 32°C, female flower abortion, fertilization failure, and male pollen sterility are pronounced[2][3][4]. International research reports similar thresholds; Japanese cultivar guides often do not state a fixed value, with some variation by cultivar and hot-year conditions.
  • Notes: Japanese sources frequently cite “poor fruit set in heat”; risk is prominent around 30–32°C, consistent with overseas literature.

5. Fruit Set & Early Fruit Development Stage ​

  • optimal_min: 18°C
  • optimal_max: 25–28°C
  • base_temperature: 10–12°C
  • low_stress_threshold: Below 15°C, growth is delayed and fruit enlargement is poor[8][9][10].
  • high_stress_threshold: Above 30°C, fruit set rate drops and enlargement may stop[6][8][13][14].
  • max_temperature: 35°C (rind abnormalities and quality loss)[8][9].
  • frost_threshold: Young fruit dies in frost; disease incidence increases[6][8][13][14][15].
  • Notes: Hot periods cause small fruit, misshapen fruit, and fruit drop.

6. Fruit Ripening & Maturation Stage ​

  • optimal_min: 18°C
  • optimal_max: 25°C
  • base_temperature: Not clearly defined (likely around 10–12°C)
  • low_stress_threshold: Prolonged periods below 15°C delay ripening and reduce storability[8][10][12][13].
  • high_stress_threshold: Above 30°C, sunscald, rind and quality decline, and disease increase[8][9][10][12][13].
  • max_temperature: 35°C
  • frost_threshold: Freezing damages fruit during growth and after harvest (storage at 10–13°C is strongly recommended)[12][15].
  • Notes: Post-harvest curing at 25–30°C; long-term storage at 10–13°C / 50–70% RH[1][5][12].

7. General Notes & Data Gaps ​

  • All green aboveground tissue is fully frost-sensitive—“immediate death on frost exposure” is emphasized across multiple sources[6][8][9][10][12][13][14][15].
  • Fruit chilling injury: Below 10°C (especially below 5°C), flesh browning and water-soaked rot risk (store at 10–13°C)[1][5][12].
  • Cultivar and regional differences: Japanese pumpkin (C. moschata) tends to be more heat- and humidity-tolerant than Western pumpkin (C. maxima), but numeric differences are not clearly stated in major guides[9][13].
  • Missing or unclear data:
    • base_temperature lacks heated-trial data and is largely reference values.
    • Low/high stress thresholds are often qualitative, expressed as ranges from experience and quality disorders.
    • sterility_risk_threshold is stated as 32°C in overseas sources; Japanese cultivar guidance emphasizes cultivar and environment dependence without fixed numeric rules.
  • Reasons for estimates:
    • Extension guides prioritize practical management over precise temperature bands, especially under recent climate variability.
    • Detailed physiological data for major Japanese cultivars are limited, so international literature fills gaps.

Parameter Definitions ​

  • optimal_min / optimal_max: Temperature range where growth, physiological activity, yield, and quality are maximized at that stage.
  • base_temperature: Minimum physiological temperature required for that process (growth stops below this).
  • low_stress_threshold / high_stress_threshold: Temperature range where stress first appears—disorders, low yield, quality loss, or growth delay.
  • max_temperature: Maximum temperature at which growth stops or damage/death occurs.
  • frost_threshold: Minimum air temperature causing lethal injury to that tissue/process (typically 0°C; must stay above 0°C).
  • sterility_risk_threshold (flowering only): Temperature at which male/female fertilization and pollination function decline sharply (reduced fruit set).

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Conclusion ​

Pumpkin has a clear and narrow temperature adaptation window at each growth stage; temperature management at germination, seedling, flowering, fruit set, and ripening is key to stable production, yield, and quality. Although Japanese and international sources show slight numeric variation, most agree that roughly 17–25°C is a broadly ideal range, with maximum caution for poor fruit set and sterility above 30–32°C and for frost vulnerability. Much Japanese material is experience-based; gaps can be filled from international and physiological reports. More detailed cultivar-specific physiological data and validation under new growing conditions remain important research needs.

Sources ​

[1] Pumpkin Production - Penn State Extension: https://extension.psu.edu/pumpkin-production/
[2] Pumpkin Critical Temperature Thresholds - The Long Paddock: https://data.longpaddock.qld.gov.au/static/dcap/DCAP3/DCAP 3__10 Pumpkin CTT Final.pdf
[3] Flowering, Sex Expression, and Fruiting of Pumpkin (Cucurbita sp.) under Various Temperatures - ResearchGate: https://www.researchgate.net/publication/277744936_Flowering_Sex_Expression_and_Fruiting_of_Pumpkin_Cucurbita_sp_Cultivars_under_Various_Temperatures_in_Greenhouse_and_Distant_Field_Trials
[4] Flowering, sex expression, and fruiting of pumpkin (Cucurbita sp) - SciSpace: https://scispace.com/pdf/flowering-sex-expression-and-fruiting-of-pumpkin-cucurbita-4g9a5y6qd8.pdf
[5] Squash, Pumpkin and Winter | College of Agricultural Sciences - Oregon State University: https://horticulture.oregonstate.edu/oregon-vegetables/squash-pumpkin-and-winter
[6] カボチャの栽培 - Hide Farm Management Consultant: https://www.hidefmc.com/kabocha/
[7] かぼちゃの栽培方法 ～種まきから収穫まで解説!仕立てや人工授粉 - Takagi: https://www.takagi-member.jp/contents/detail/443?srsltid=AfmBOoodU5hCRsYY1UHU27xFUdGfA83vH5ZMosgC7GA9YRwCkjVewkwn
[8] カボチャ (Squash) - Atariya: https://www.atariya.net/yasai/kaboch.htm
[9] カボチャの育て方・栽培方法 - 園芸通信 (Sakata Seed): https://sakata-tsushin.com/lesson-vegetable/detail_33/
[10] カボチャ - 野菜栽培マニュアル ｜ 調べる - タキイ種苗: https://www.takii.co.jp/tsk/manual/kabocha.html
[11] Cucurbit Crop Growth and Development Germination and Emergence - Purdue University: https://www.agry.purdue.edu/cca/2007/2007/Proceedings/Liz Maynard-CCA proceedings 1_KLS.pdf
[12] カボチャ - MAFF栽培指針: https://www.maff.go.jp/j/seisan/kankyo/hozen_type/h_sehi_kizyun/attach/pdf/aki3-4.pdf
[13] カボチャの育て方・栽培方法 - Sakata通信: https://sakata-tsushin.com/lesson-vegetable/detail_33/
[14] カボチャ | 野菜のビギナーズマニュアル | 株式会社トーホク: https://www.tohokuseed.co.jp/beginners/kabocha.html
[15] カボチャの上手な栽培方法・育て方 | タキイネット通販: https://shop.takii.co.jp/selection/kabocha2011.html

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