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Seed Stratification

From seed to sprout

Seeds of native prairie species have built-in dormancy mechanisms that prevent them from germinating (sprouting) until growing conditions favor survival of the seedling plants. This is one of Nature’s ways of ensuring species survival. Depending on the species, seeds will not break dormancy under too wet or too dry growing conditions, imminent winter conditions, or high temperatures. Some seeds do best planted fresh - in general, our spring ephemerals and many sedge species. Some seeds require light to germinate. Some have fuzzy seedcoats which shed water or very hard seedcoats which seal water from the embryo plant. Some hard-coated species benefit from fire, which weakens the seedcoat so that it can absorb water. Some seeds have chemical inhibitors to germination and benefit from chemical action, such as would naturally occur during transit through a bird’s digestive system, for instance. But helping most seeds germinate isn’t complicated.

Many prairie species require about two months of cold, damp conditions before they will germinate - what they would ordinarily experience over winter. You can plant late in the fall (late November in Iowa, or frost seed by end of January) and let Mother Nature do this work. If you are planting in the spring, you must have artificially imitated Nature's cycle by stratifying your seed so that it will germinate: mix seed (keep species separate) with a sterile medium(builder’s sand from lumber supply company or vermiculite from greenhouse nursery), at a ratio of one part seed to 2-3 parts medium, and add water. A sterile medium is recommended to prevent mold growth. The seed mixture should be nicely damp, but not so moist that you can squeeze water out of it. Place in clean plastic bag and store in refrigerator for two months. Start checking periodically after 4-5 weeks for germination - if seed has started to sprout, you must plant. You must time this method so that germination is coordinated with outside growing conditions if you are not using a greenhouse, and is not advised unless you can provide water for seedling plants.

Some hard-seeded prairie species (particularly legumes) benefit from scarification to make a hard seedcoat less impervious to water: place seed between two sheets of medium-grade sandpaper and rub to abrade the seed. Examine progress with a hand lens or magnifying glass - you want to scratch, not crush, the seed. Then proceed with cold/moist stratification if required.

Helping seed grow is fun, and pretty soon you’ll be into the serious stuff like the boiling water method for New Jersey tea! For help with individual species germination requirements, several good resources are available (not meant to be an exhaustive list nor in any particular order of recommendation):

  • Prairie Propagation Handbook, available from the Wehr Nature Center in Franklin, WI. 

  • The Tallgrass Restoration Handbook for Prairies, Savannahs, and Woodlands by Packard and Mutel, Society for Ecological Restoration. 

  • Restoring the Tallgrass Prairie, An Illustrated Manual for Iowa and the Upper Midwest by Shirley Shirley.

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