Comprehensive research report on cumulative temperature (GDD) requirements for each main growth stage of broccoli (Brassica oleracea var. italica)

Overview

This report describes the cumulative temperature (Growing Degree Days, GDD) is compiled from the most reliable sources possible, based on domestic and international peer-reviewed papers, public institutions, agricultural guidelines, etc. If the direct GDD value has not been reported, clearly indicate the estimated value calculated using the number of days, actual measurements, or standard temperature, base temperature, and optimal temperature, and clearly state the basis, assumptions, and precautions. It assumes general open-field cultivation, especially in temperate regions.

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Definition and calculation method of cumulative temperature (GDD)

• **GDD (Growing Degree Days)** is the cumulative value of temperature required for a crop to grow to a certain level.
• General formula:
  GDD = Σ [(daily maximum temperature + daily minimum temperature) / 2 - reference temperature (Tbase)]
• **The standard temperature (Tbase)** for broccoli is often 4°C (40°F), but some Japanese studies have also used 7.2°C [1][2][3][4].
• Optimum temperature is 16-24°C, with slight variations at each stage [5][6][7].
• Since detailed settings and thresholds differ depending on the model, region, and variety, please clearly state the Tbase for each source when quoting numerical values.

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Cumulative temperature (GDD) requirements for each growth stage

1. Germination

• Period: 2-3 weeks (approximately 14 days) until transplanting
• Optimal temperature: 16-18°C (mainly spring and autumn sowing in temperate zones) [5][6][7][8]
• Estimation method (Tbase=5°C, period 14 days, average temperature 17°C):
  • {(17 + 17) / 2} - 5 = 12 GDD/day × 14 days = 168 GDD
• Caution: It will vary depending on the difference between open field/house, cell seedling raising, and direct sowing. Planting is often seen as the turning point to the next stage.
• Reference: [5][6][7][8]

3. Vegetative Growth

• Direct GDD value available. Many studies report cumulative temperatures from planting to flower bud formation/head set in the following ranges:
  • 400 to 600 GDD (Tbase 4 to 5°C) GDD)" → "starting stage of flower bud differentiation" [9][10][11][12]
• Japanese research example: Analyzed using a model that assumes 7.2°C as Tbase, but 4-5°C is also used as a reference to emphasize international consistency [1][2][9]
• Caution: Day length, effective photosynthetic radiation, and extreme temperatures (especially high temperatures) are closely related to the timing and success or failure of flower bud formation [10][11].
• Reference: [1][2][9][10][11][12]

5. Flowering / Harvest

• From flower bud formation to flowering and harvest, in many cases the marketable head** is finally reached at 750-950 GDD (Tbase 4-5°C).
  • Example: Approximately 400-600 GDD from planting to flower bud formation, then an additional 150-300 GDD until harvest time[2][9][12][13]
• Flowering itselfIn many cases, the product does not meet the product specifications, so the actual harvest management should be based on the ``enlarged state of the flower buds just before flowering.''
• Precautions:
  • At high temperatures (>24-27°C), rapid flower bud differentiation, flowering, and fading occur quickly [10][11].
  • Extreme weather conditions and lack of irrigation and fertilization can also cause discrepancies in GDD digestion efficiency and actual growth stage.
• Reference: [2][9][12][13]

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Summary table of cumulative temperature requirements for each stage (Tbase=5°C rough guide)

Stage	GDD (estimated value/literature value)	References
Germination stage	Approx. 150 GDD	[5][6][7]
Seedling stage	Approx. 170 GDD	[5][6][7][8]
Vegetative growth stage	400-450 GDD	[6][7][8][9]
Flower bud formation period	400-600 GDD	[1][2][9][10][11][12]
Harvest period (until harvest)	750-950 GDD	[2][9][12][13]

Try it in your region

See how these GDD requirements apply to your local weather data. Simulate Broccoli cultivation →

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Notes and data gaps

• Difference between GDD division and stage division: There are few studies that clearly divide GDD by stage, and in reality there is a high degree of continuity between germination and planting, nutrition and reproduction.
• **Temperature stress (especially high temperature)** has a large effect, and even if the GDD is the same, there will be differences in growth progress and quality [10][11].
• Differences in variety/environment (sowing period, cultivation area, day length, etc.) affect requirements. GDD needs to be used as a "just in case".
• Primary information in Japanese is small, but there is also an example of a standard temperature 7.2°C model, and consideration should be given to comparing and handling it with international information that uses 4 to 5°C [1].
• It is appropriate to use GDD as "an indicator" that interacts not only with the daily average but also with the extreme values ​​of minimum and maximum temperatures, day length, and management techniques.

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Overview

• Estimated cumulative temperature requirement (Tbase 5°C standard) for each developmental phase of broccoli is approximately 300°C from germination to seedling stage GDD is weak, vegetative growth period is 400-450 GDD, flower bud formation is cumulatively 400-600 GDD, and harvest period is distributed at cumulatively 750-950 GDD.
• Direct literature values mainly focus on flower bud formation and harvesting period, and subdivisions from germination to seedling/vegetative stages are largely based on estimates.
• The cumulative temperature model should be used as a guideline and predictive indicator for management in actual cultivation.Local weather, variety, and stress factors must also be considered in the management strategy.

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Sources

[1] Increasing the Yield of Broccoli (Brassica oleracea L.) (Japanese: cumulative temperature 7.2°C model): https://www.jstage.jst.go.jp/article/hortj/advpub/0/advpub_OKD-143/_pdf/-char/ja
[2] Predicting broccoli development | Request PDF - ResearchGate: https://www.researchgate.net/publication/240423868_Predicting_broccoli_development
[3] Data Requirements for Supporting Registration of... (Tbase international comparison): https://www.acis.famic.go.jp/eng/shinsei/8147_e.pdf
[4] Determining Heat Unit Requirements for Broccoli: https://journals.ashs.org/jashs/view/journals/jashs/122/2/article-p169.pdf
[5] 4 Stages of Broccoli Growth - Spider Farmer: https://www.spider-farmer.com/blog/broccoli-growing-stages/
[6] The 4 Broccoli Plant Growing Stages (With Pictures) - The Spruce: https://www.thespruce.com/broccoli-plant-growing-stages-7254306
[7] How to Grow Broccoli - MSU Extension: https://www.canr.msu.edu/resources/how_to_grow_broccoli
[8] Growing Broccoli for Beginners | WVU Extension: https://extension.wvu.edu/lawn-gardening-pests/gardening/gardening-101/growing-broccoli-for-beginners
[9] Plant Growth and Development of Broccoli - Encyclopedia.pub: https://encyclopedia.pub/entry/35086
[10] The heat-sensitive stage of broccoli flower development: http://www.hort.cornell.edu/bjorkman/lab/broccoli/broccoli.php
[11] Prediction of time to harvest and its variability in broccoli (Brassica ...): https://www.sciencedirect.com/science/article/abs/pii/S0304423815303459
[12] Final report for GS21-246 - SARE Grant Management System: https://projects.sare.org/project-reports/gs21-246/
[13] Final Report for FNE11-718 - SARE Grant Management System: https://projects.sare.org/project-reports/fne11-718/