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Getting
Ready for Springtime:
Seed Stratification
By
Glenda Buenger
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. (414) 425-8550.
Last time I checked, it still cost only $4.95, a good addition
to your prairie library, and close to if not already considered a
classic.
The
Tallgrass Restoration Handbook for Prairies, Savannahs, and Woodlands by
Packard and Mutel, Society for Ecological Restoration.
Available from
Island
Press, 1-800-828-1302; www.islandpress.org
This book is already considered a landmark of restoration
knowledge.
Restoring
the Tallgrass Prairie, An Illustrated Manual for Iowa and the Upper
Midwest by Shirley Shirley. Available
from the University of Iowa Press, 1-800-621-2736; www.uiowa.edu/~uipress
. A very useful book which contains
propagation methods and drawings of seedling plants.
Catalog
and Cultural Guide, self-published by Alan Wade with members of the Wiscoy
Valley Land Cooperative, Prairie Moon Nursery, Winona, MN.
(507) 454-5238; pmnrsy@luminet.net; www.prairiemoonnursery.com;
atalog is free or you can try downloading it from the webpage if you have
Adobe
Reader. The cultural guide contain
information
about germination requirements for individual prairie, woodland, and wetland
species.
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