Many tree seeds need stratification, a stretch of moist cold or warmth that mimics the seasons, because chemical inhibitors or an unripe embryo keep them dormant until winter has passed. At home, seeds are held in damp peat moss in a sealed bag, refrigerated for cold or kept at room temperature for warmth, for the days the species needs.

Why do tree seeds stay dormant without stratification?

Because dormancy times germination to a season that favors a seedling's survival. In many species, inhibitors such as abscisic acid block sprouting until cold, moist conditions break them down, while others have immature embryos that need a warm phase first.

How is cold stratification done at home?

With damp peat moss, a sealed bag, and a refrigerator:

• Soak peat moss, then squeeze out as much water as possible
• Layer the seeds in the damp peat inside a zip lock bag and seal it
• Keep the bag in the bottom of the refrigerator, about 1 to 5°C (34 to 41°F)
• Check it occasionally and sow early sprouts

How long does stratification take for common trees?

Cold periods from the seed listings:

• Red maple: 30 days
• Paperbark birch and Japanese black pine: 60 days
• Himalayan white pine and Full Moon Japanese maple: 90 days
• Southern magnolia and Bloodgood Japanese maple: 120 days

How are seeds that need warm and cold stratification handled?

In sequence, warm first at 72 to 86°F, such as on top of the refrigerator. Because a warm phase lets an immature embryo finish growing before the chill, Japanese Tree Lilac Seeds are held at room temperature for 60 days and then refrigerated for 60 more.

Frequently Asked Questions

Can seeds be stratified in the freezer?

No. Cold stratification works just above freezing, in the 1 to 5°C range a refrigerator holds.

What should be done if mold appears in the bag?

Moldy seeds come out, and the rest go into fresh, slightly drier peat. Mold usually signals a medium that was too wet.

Can sand or paper towels replace peat moss?

Usually, yes. Any clean medium that stays evenly damp without dripping can hold seeds through stratification.

Do warm and cold periods add up?

Yes. At 120 days warm followed by 90 days cold, Giant Dogwood Seeds are bagged for about seven months before sowing.