Seed Stratification



I came home from work one day last week and the area around our house was littered with green ash seeds (actually fruits). The wind was not particularly strong that day, so apparently the seeds were simply ready to take the trip.

Those winged fruits or samaras occasionally provide kids with some good entertainment. I suspect a good share of you have thrown them up in the air and watched them “helicopter” down to earth a few feet away. I did it again last week!

Seeds are amazing things. There is so much going on in them, but we seldom give it much consideration. Like most seeds of plants native to temperate climates such as ours, the seeds of ash will not germinate until they have gone through a cold period. This cold treatment or “stratification” allows the seed time to be dispersed, and more specifically, withstand the cold harsh conditions of winter. If the seeds were to germinate immediately they would not disperse far from the parent tree, and they certainly would not survive the winter.

Seed dormancy is a function of the seed coat and/or embryo development. Sometimes the seed coat and/or embryo are not ready even though the correct germination conditions are present. That is dormancy. At other times the seed conditions are ready to go but the environmental conditions for germination are not present. That is called quiescence. Either way, the timing mechanisms work beautifully.

The seeds of ash start to fall as soon as they are ripe. But they still need that cold treatment or stratification. The seeds do not have to freeze; they just need several weeks of near freezing conditions. There is some evidence that these cold temperatures are actually required for certain proteins or enzymes to stimulate growth.

If you ever try starting some of our native trees or wildflowers from seeds, remember that most of our native species need to go through a stratification. Do not keep the seeds in the house over the winter. Keep them in a cold place, such as an unheated garage. You could even plant the seeds before winter sets in. Either way, they should get the required cold treatment.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.



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