Appearance
Comprehensive Survey of Growing Degree Days (GDD) by Growth Stage for Carrot
Overview
This report summarizes required Growing Degree Days (GDD) for each growth stage of carrot (Daucus carota L.)—germination, leaf/stem elongation and vegetative growth, root enlargement, and flowering/bolting—based on current Japanese primary literature and international scientific papers, with base and optimal temperatures. Where direct GDD values are not reported, estimates are derived from reliable indirect data, days, and temperature data. Base temperature (Tbase) and optimal growth temperature for each stage are also stated.
What Is GDD?
Growing Degree Days (GDD) evaluate how much temperature has accumulated at each growth stage, generally calculated as the daily sum of (daily mean temperature − base temperature). Base temperature (Tbase) varies by crop and stage; for carrot, 5°C (to 8°C) is mainly used in Japanese and international literature [1][2][3][4].
1. Germination
Base and Optimal Temperature
- Germination base (minimum) temperature: about 8°C [1][2]
- Optimal germination temperature: 15–25°C; no germination above 35°C [2][3]
- At 11°C, uniform germination in about 20 days; more than 30 days at 8°C [2]
Required GDD
- No direct "required GDD" for germination stage in Japanese literature [1][2].
- Papers and agricultural materials report high germination rate at accumulated temperature above 40°C under 0–5°C low-temperature germination [4].
- International literature (MDPI, 2024) uses Tbase=5°C and defines GDD range to end of seedling stage (SS) as "below 948 (Tbase=5°C)" [5]. Thus germination/seedling proceeds essentially from GDD 0 to 948.
Summary
- GDD from germination to end of cotyledon stage: about 0–950 (Tbase=5°C, international standard) [5]
- Japanese primary literature lacks "accumulated temperature ○°C for germination" format but conversion from germination optimal/base temperature and days is possible.
2. Leaf and Stem Elongation / Vegetative Growth
Base and Optimal Temperature
- Optimal growth temperature: 15–25°C [6][7]
- Growth and root enlargement suppressed below 10°C and above 30°C [7]
- Root length determination for summer-sown autumn harvest around 70 days after sowing (varies by cultivar) [7]
Required GDD
- Little direct GDD reporting for this stage in Japanese literature.
- International literature (MDPI, 2024) classifies Vegetative Stage (VS = leaf/stem elongation and vegetative growth) from SS end (GDD 948) to "below 1513 (Tbase=5°C)" [5].
→ GDD range for leaf/stem elongation and vegetative growth is about 950–1510.
Summary
- Leaf/stem elongation and vegetative growth: GDD about 950–1510 (Tbase=5°C)
- Few explicit Japanese examples; international standard conversion from growth rate and root length timing is a useful reference.
3. Root Enlargement
Base and Optimal Temperature
- Optimal temperature for root enlargement: 18–21°C [7]
- Enlargement stops below 3°C; suppressed below 10°C and above 30°C [7][8]
Required GDD
- No explicit GDD from root enlargement start to harvest in Japanese primary papers.
- International literature defines Root Enlargement to Harvest as "below GDD 1968 (Tbase=5°C)" [5]. Root enlargement start is around GDD 1513 (VS end); enlargement end around GDD 1968. → Practical root enlargement period GDD is about 1510–1970.
Summary
- Root enlargement: GDD 1510–1970 (Tbase=5°C)
- Applicable as modern field cultivation and harvest maturity guideline.
4. Flowering / Bolting
Base and Optimal Temperature
- Flower bud differentiation and flowering optimal: 10.87°C–22.37°C (international paper) [9]
- Japanese literature reports increased bolting risk at accumulated temperature below 1,314°C [10]
Required GDD
- No direct GDD to bolting/flowering in Japanese primary papers.
- International literature uses high GDD accumulation (e.g., after 1513) as indicator for bolting/flowering equivalent stages [5]
- In practice, low-temperature exposure before sufficient GDD (below 1314°C accumulated) increases bolting risk [10]
Summary
- No clear GDD division to bolting/flowering stage even in international literature.
- Bolting is likely when low-temperature exposure occurs before reaching about GDD 1300 from germination
5. GDD Summary Table by Growth Stage (Recommended Standard)
| Growth Stage | GDD Range (Tbase=5°C) | Notes |
|---|---|---|
| Germination to cotyledon | 0–950 | Japanese literature centers on germination days and temperature |
| Leaf/stem elongation, vegetative growth | 950–1510 | Mainly international reporting |
| Root enlargement | 1510–1970 | |
| Bolting / flowering | 1300–1970+? | Many uncertainties (lower limit only) |
Try it in your region
See how these GDD requirements apply to your local weather data. Simulate Carrot cultivation →
6. Japanese Data Gaps and Future Tasks
- Explicit GDD per growth stage is very limited in Japanese primary scientific papers.
- Using international agronomic values (Tbase=5°C) as practical indicators and comparing with field observation, days, and temperature is currently most reasonable.
- Accumulation of Japan-specific data on GDD to bolting/flowering and fine regional and cultivar differences for winter and summer sowing is desirable.
Conclusion
This survey integrates GDD requirements by carrot growth stage from Japanese and international sources, with estimates where direct values are unavailable. International Tbase=5°C ranges provide practical field guidance; local climate and cultivar adjustment remain important.
Sources
[1] Spring-sown carrot and burdock bolting before harvest, Snow Seed PDF: https://www.snowseed.co.jp/wp/wp-content/uploads/grass/grass_196005_03.pdf
[2] Improving carrot germination rate, Kagoshima Prefecture PDF: https://www.pref.kagoshima.jp/al08/chiiki/nansatsu/sangyo/nougyou/gijutsu/documents/62039_20171005192314-1.pdf
[3] Carrot: timely sowing and irrigation for reliable germination - JA Saitama: https://www.ja-saitama.or.jp/wp/?p=9422
[4] MHLW Health and Labour Sciences Research Results Database: https://mhlw-grants.niph.go.jp/system/files/2014/142021/201407025A/201407025A0020.pdf
[5] Optimal Timing of Carrot Crop Monitoring and Yield Assessment ..., MDPI 2024: https://www.mdpi.com/2076-3417/14/9/3636
[6] Cropping season and suitable cultivars for summer-sown autumn-harvest carrot in Miura Peninsula: https://agriknowledge.affrc.go.jp/RN/2010941264.pdf
[7] Fertilization Science - BSI Bio Carrot: http://bsikagaku.jp/f-fertilization/carrot.pdf
[8] Iwate Prefectural Agricultural Research Center Report No. 11: https://www.pref.iwate.jp/agri/nouken/ronbun/noushi/noushi_11.html
[9] Phenological phase affects carrot seed production sensitivity ..., ScienceDirect: https://www.sciencedirect.com/science/article/pii/S0048969723031236
[10] Growth of spring cabbage and autumn-winter radish under climate change, TUAT Repository: https://tuat.repo.nii.ac.jp/record/1897/files/202103TakadaAtsushi_F.pdf