Spinach — GDD Requirements by Growth Stage

Overview

This report surveys GDD (Growing Degree Days) for spinach (Spinacia oleracea) across three stages—germination, vegetative growth, and bolting/flowering—from reliable academic and extension sources. Where stage-specific GDD is unavailable, reasonable estimates use days, temperature, and base temperature (T_base) from guides and research, with calculation assumptions explained.

GDD Basics for Spinach

GDD = {(T_max + T_min)/2} − T_base

• T_base for spinach: 4.4°C (40°F), consistent in Japanese and international sources[1][2].
• Optimal germination: 15–20°C (rate declines above this)[3][4][5].
• Vegetative optimum: 15–20°C after germination; above 20°C, growth slows and bolting risk rises[5][6].

Stage Assumptions for GDD Estimation

• T_base: 4.4°C
• Mean temperature: 15°C (conservative optimum per stage); longer duration in cold regions.
• Days: Germination 10 days; vegetative 35 days (midpoint); ~45 days total to bolting (varies by cultivar and environment).
• Stage GDD = (mean temperature − T_base) × days.

Germination GDD

• Optimal temperature: 15–20°C[3][4][5]
• Duration: 5–14 days; ~10 days typical[3][5][6]
• Estimate: (15 − 4.4) × 10 ≈ 106 GDD (~100–120 GDD at 15–16°C over 10 days)

Vegetative GDD (Post-germination to Pre-bolting)

• Optimal: 15–20°C; growth stalls above 20°C[5][6]
• Duration: 28–42 days[6][7]
• Estimate: (15 − 4.4) × 35 ≈ 373 GDD (~350–470 GDD at 15–17°C over 28–42 days)

Bolting / Flowering

• Triggers: Day length 13+ hours plus temperatures above 20°C[6][8][9]
• GDD role: Day length is critical; GDD alone is not a direct threshold for bolting.
• Cumulative to bolting start: ~106 + 373 ≈ 480 GDD (estimate)
• Sources state bolting cannot be managed by GDD threshold alone[6][8][9].

Stage GDD Summary (Estimates)

Stage	Days (guide)	Mean temp	Estimated GDD (°C·days)
Germination	5–14	15–20°C	50–150
Vegetative	28–42	15–17°C	300–470
Bolting / flowering	—	—	~480 GDD cumulative to pre-bolt; bolting driven mainly by day length and heat

Try it in your region

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

Calculation Caveats

• Estimates use typical days and temperatures from literature; actual values vary by site, sowing date, and cultivar (early vs. slow-bolting).
• Bolting is driven more by long days and high temperature than by GDD alone.

Conclusion

• GDD guides germination (~100 GDD) and vegetative/harvest period (~350–470 GDD; ~450 GDD total pre-bolt).
• Bolting requires day length 13+ hours and temperatures above 20°C—GDD alone cannot control it; adjust sowing date and season.
• No major guide recommends GDD-only bolting prediction.
• Use local measured temperatures for best results.

Sources

[1] Growing Degree Days - Cultivation Ag: https://cultivationag.com/growing-degree-days/
[2] Base and upper temperature thresholds to support the calculation of growing degree days and crop coefficients in the FAO56rev guidelines - Agricultural Water Management (2025): https://www.sciencedirect.com/science/article/pii/S037837742500469X
[3] Effect of Temperature on Seed Germination in Spinach (Spinacia oleracea L.): https://journals.ashs.org/view/journals/hortsci/51/12/article-p1475.xml
[4] Growing Spinach: Complete Life Cycle Guide - Vaki-Chim: https://growplant.org/blog/spinach-life-cycle/
[5] タキイのホウレンソウ栽培マニュアル（日本語）: https://www.takii.co.jp/tsk/manual/pdf/hourensou.pdf
[6] ほうれん草の生態に関する研究（第1報）: https://iwate-u.repo.nii.ac.jp/record/11471/files/erar-v5n2p22-35.pdf
[7] How to Grow Spinach - MSU Extension: https://www.canr.msu.edu/resources/how_to_grow_spinach
[8] 営農改善指導基本方針 北海道農政部: https://www.pref.hokkaido.lg.jp/fs/1/1/2/8/9/3/2/0/_/令和2年営農改善指導基本方針.pdf
[9] Growing Spinach, A Cool-Season Vegetable - Penn State Extension: https://extension.psu.edu/growing-spinach-a-cool-season-vegetable