Radish (Daikon) — Temperature Requirements by Growth Stage

Overview

Radish (daikon) is a cool-season root crop whose cycle includes germination, seedling (leaf growth), root enlargement, and flowering (bolting). Appropriate temperature at each stage is critical; departure from optimal ranges risks poor germination, root quality loss, bolting, and pollen sterility. Using authoritative Japanese and academic sources, this report tabulates optimal_min, optimal_max, base_temperature, low_stress_threshold, high_stress_threshold, max_temperature, frost_threshold, and sterility_risk_threshold (flowering only) by stage. Cultivar and regional differences are noted where documented; otherwise general values are given.

Temperature Requirements Summary by Growth Stage

Stage	optimal_min	optimal_max	base_temperature	low_stress_threshold	high_stress_threshold	max_temperature	frost_threshold	sterility_risk_threshold (flowering only)	Notes
Germination	18°C	24°C	4–5°C	4°C	25°C	—	4°C	—	No cultivar/regional values stated
Seedling / leaf growth	10°C	18°C	4–5°C	−4°C	29°C	29°C	−4°C	—	Heat/bolting tolerance varies by cultivar
Root enlargement	10°C	18°C	4–5°C	−4°C	29°C	29°C	−4°C	—	Cultivar and harvest timing differ
Flowering (bolting)	10°C	18°C	4–5°C	−4°C	29°C	29°C	−4°C	30–32°C (estimated from related crops)	No radish-specific value found

Parameter Definitions and Rationale

• optimal_min / optimal_max: Germination is best at 18–24°C; subsequent growth and root enlargement at 10–18°C. Germination rate and uniformity decline above 25°C[1][2].
• base_temperature: 4–5°C for germination and growth; below this, growth stops or germination fails[3][4].
• low_stress_threshold / frost_threshold: Seedlings and roots tolerate to about −4°C; below that, injury or death occurs. Harvest before hard frost (−4°C or below) is recommended[2][3][5].
• high_stress_threshold / max_temperature: Above 29°C, growth is poor and bolting advances; 29°C is a practical upper limit[2][3].
• sterility_risk_threshold: No radish-specific data; related brassicas suggest increased pollen sterility and poor seed set above 30–32°C (estimate)[6].
• Cultivar/regional differences: Heat-tolerant and slow-bolting types are recommended for warm/tropical systems; specific thresholds are often in catalogs and trials[3][2].

Detailed Stage Descriptions

Germination

• Optimal 18–24°C; germination possible near 5°C but slower at low temperature. Above 25°C, germination rate falls.
• ~4°C is effectively the base temperature; extreme cold below 4°C risks injury though germination cold tolerance is relatively high.

Seedling / Leaf Growth

• Optimal growth 10–18°C; above 29°C, root enlargement is poor and immature plants bolt easily.
• Tolerance to frost to about −4°C; below that, plants die or stop growing.
• Growth likely begins around 5°C.

Root Enlargement

• Ideal 10–18°C, similar to leaf growth; heat and cold stress need more attention than in leaf stage; above 29°C enlargement is inhibited and quality drops.
• Hard frost (−4°C or below) can damage roots—harvest before severe frost.
• Peak enlargement and harvest timing vary slightly by cultivar.

Flowering (Bolting)

• Similar optimal and heat-stress conditions to root enlargement; above 29°C, bolting and flowering are promoted.
• Related brassicas: above 30–32°C, pollination failure and poor seed set are possible; radish-specific values are not stated.
• Flower initiation and sterility risk vary by cultivar and region—consult local guides and seed catalogs.

Cultivar and Regional Differences

• In Japan, cultivars differ in heat tolerance and bolting resistance; early vs. late types and heat tolerance affect success in warm regions.
• Specific thresholds may appear in catalogs and trials—refer to local extension materials when selecting cultivars.

Try it in your region

See how these temperature requirements apply to your local weather data. Simulate Radish cultivation →

Sources

[1] Growing Daikon Radish April Cross: https://growcycle.com/seed-directory/daikon-radish-april-cross?srsltid=AfmBOorRmJLRlvAfgi7ZdmI0EoTWLze3wetnTQrPjys9EBx3nSNUcNHK
[2] Daikon – Growing Guide - Deep Green Permaculture: https://deepgreenpermaculture.com/2025/08/16/daikon-growing-guide/
[3] Daikon Radish Cultivation Guide for Florida: https://edis.ifas.ufl.edu/publication/HS1370
[4] Daikon Radish Seeds | Sow True Seed | Open Pollinated: https://sowtrueseed.com/products/radish-daikon-japanese-minowase?srsltid=AfmBOoqUr7e46Np4_cLfAcPEHLoTgEkSolgiSlYZDiSVxNFJ-l5zT_c6
[5] Growing Daikon Radish: Massive And Mild-Flavored - Epic Gardening: https://www.epicgardening.com/growing-daikon-radish/
[6] Best Temperature & VPD for Flowering Stage Outdoors 2025: https://farmonaut.com/blogs/best-temperature-vpd-for-flowering-stage-outdoors-2025

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When planning detailed temperature settings and cultivation schedules for your region and goals, also consult local extension services and cultivar-specific manuals.