Cold stratification by species (table)
Cold moist stratification is a pre-germination treatment that mimics the natural winter dormancy-breaking process. Many seeds from temperate climates require a period of cold, moist conditions before they will germinate -- a safeguard against germinating in fall before winter. Per NC State.
Cold moist stratification is a pre-germination treatment that mimics the natural winter dormancy-breaking process. Many seeds from temperate climates require a period of cold, moist conditions before they will germinate — a safeguard against germinating in fall before winter. Per NC State Extension, this physiological dormancy is overcome by holding seeds at 35—40°F in moist medium for a species-specific period, ranging from 30 days to over 6 months.
Without stratification, these seeds either fail to germinate at all or germinate poorly and irregularly.
How cold stratification works
Per Penn State Extension, seed dormancy in temperate species is maintained by germination inhibitors (abscisic acid and related compounds) in the seed coat or embryo. Cold-moist stratification degrades these inhibitors over time, resetting the seed's germination "permission" system. The key requirements are:
- Temperature: 34—41°F (1—5°C); 38°F is the optimal target per most sources. Below 32°F, stratification stops; below 28°F, seeds can be damaged.
- Moisture: Seeds must be hydrated throughout stratification but not waterlogged
- Aeration: Some oxygen exchange is needed; sealed containers with no ventilation can cause anaerobic conditions and rot
- Duration: Species-specific; shortening fails to overcome dormancy; extending is generally safe