Seed Stratification Techniques

Seed stratification is a cold- or warm-moist treatment that simulates winter conditions to ensure that certain seeds germinate properly. Many trees, shrubs, and native perennials need it.  Failure to do this for seeds that require it can result in zero germination.

🌱 What Is Seed Stratification?

Stratification breaks seed dormancy by exposing seeds to cold or warm, moist conditions for a specific period (typically weeks to months). Without it, seeds may sit in soil for a year or more without sprouting.

❄️ Stratification (cold-moist stratification is most common)


What you need

  • Seeds
  • Moist medium: sand, vermiculite, peat moss, or paper towel
  • Zip-top bag or container
  • Warm Temperatures (house temperatures) for warm-moist stratification or a refrigerator (NOT a freezer) for cold-moist stratification

Step-by-step

  1. Moisten the medium
    Damp, not dripping (squeeze test: no water should drip out).
  2. Mix seeds into the medium
    The medium should surround the seeds evenly.
  3. Seal and label
    Include plant name + start date + length of stratification needed.
  4. Refrigerate at 34–41°F (1–5°C) for cool-moist stratification or typically room temperature  65–72°F for warm-moist stratification
    Store in the crisper or at the back of the refrigerator.
  5. Check periodically
    1. If mold appears → rinse seeds, replace medium
    2. If seeds sprout early → plant immediately
  6. Plant after the stratification period
    Sow as directed once time is complete.

Note: If there is plenty of refrigeration space, plant seeds in pots, wrap in plastic wrap, and put the entire container in the refrigerator.

⏳ Typical Cold Stratification Times

Plant Type Time Needed
Many natives & wildflowers 30–60 days
Fruit trees (apple, pear) 60–90 days
Nut trees (oak, walnut) 90–120 days
Some shrubs (viburnum) up to 180 days

🌤️ Warm + Cold Stratification (some trees & shrubs)

Some seeds require a warm, moist period followed by cold.  For example:

1. Warm phase: 60–90 days at room temp (moist medium)

2. Cold phase: 60–120 days in the refrigerator

(Common for magnolia, pawpaw, some viburnums)

🌧️ Outdoor (Natural) Stratification

  • Sow seeds outside in the fall
  • Let winter do the work naturally
  • Best for hardy natives and woodland plants
    ⚠️ Risk: rodents, rot, uneven germination
  • Winter sowing in containers is another option that gives the seeds more protection

🚫 Common Mistakes

  • ❌ Medium too wet → mold/rot
  • ❌ Freezing seeds (freezer ≠ fridge)
  • ❌ Forgetting to label
  • ❌ Skipping stratification when required