Seed Stratification Guide to Seed Dormancy
Excerpted from: Seed Stratification Guide by Prairie Nursery
Stratification is a process of treating seeds to simulate natural conditions that seeds would
experience in the soil over-winter to break seed dormancies and initiate the germination process.
Stratification treatments are applied when the seed is being propagated in a greenhouse setting or
in a way/schedule that is not aligned with the natural germination cycle.
Seeds and seed mixes which are sown outdoors in the fall do not require stratification treatments.
Dry stratification is a seed pre-treatment in which the seed is subjected to cold temperatures of 32˚ F
or lower, for a period of a month or longer. This simple treatment of keeping the seeds in cold, dry
storage helps increase germination rates by imitating a natural winter dormant period. Many native
prairie species require only Dry Stratification.
Dry stratification can be accomplished in temperate climates by
storing the seed in Ziploc bags in a refrigerator, or in a rodent-proof container in an unheated building
over winter for 30-120 days (depending upon the species). Most warm season prairie grasses and
wildflowers require only 30 to 60 days of dry stratification to break seed dormancy.
Many prairie seeds germinate best when seeded in fall, in a dormant seeding. The exposure to cold,
damp conditions over the winter is a nature's "moist stratification," and signals to the seed that it is
time to germinate when the soil warms up in spring. Some wildflowers need this process, more than
others. A moist stratification seed treatment is used to mimic the effects of winter on the seed.
Moist stratification is a process wherein the seed is mixed with moistened inert material (fresh sawdust,
builder’s sand, vermiculite, peat moss or similar material) and stored cold for ten days to three months.
Planting the seed outside in the fall (direct seeding) achieves the same results as Moist Stratification. It
is not necessary to use Moist Stratification pre-treatment for seed that is to be planted in the fall, as
dormancy will be broken naturally in the soil over winter.
To Moist Stratify seed: In a plastic bag or re-sealable container, mix the seed with an equal volume of
moist (not wet) sawdust or clean builder’s sand (if moisture can be squeezed out of the sawdust or
sand, it is too wet). Refrigerate at 34-38 degrees F (do not freeze!). Most flower seeds require 3-4 weeks
of treatment. Legume seeds generally only require ten to fifteen days. Some flowers require two to three
After removing the moist stratified seed from the refrigerator, it can be sown in pots or flats, or diluted
with a much larger volume of inert carrier material and direct-seeded onto the soil.
When planting moist stratified seed, it is best to water the area for one to two months after seeding.
Seed may revert to dormancy if it does not receive rain or moisture within a certain number of days
after planting. All direct seedlings in spring or early summer, pre-treated or not, will benefit from irrigation
during the first two months after seeding.
Members of the legume or bean family can benefit from an inoculation with Rhizobium bacterium
prior to planting. All of our legume seeds have been pre-inoculated with this bacterium. The bacterium
works with the plant to form nodules, on the roots of legume plants, which are capable of taking nitrogen
from the atmosphere and incorporating it into the plant.
Inoculant, which is usually a mixture of the bacteria and peat, can be purchased and applied to seed.
Pre-inoculated seed can also be purchased from various seed vendors. It is vital that the best methods
are used when applying inoculant to seed, during storage, and during planting. Different types of bacteria
are used for different species of legumes. Be sure to purchase the correct inoculant for the species
being planted. During purchasing, be sure to buy the correct inoculant for the species planted and to
read the tag. It is essential that the bacteria have contact with the roots.
Scarification of seed is the process of scratching the seed coat to allow moisture to enter the seed itself.
If a seed requires scarification, gently scratch the seed with a sandpaper block or sharp blade prior to planting outdoors,
or prior to moist stratification. Many members of the pea family (legumes) benefit from scarification.
The seeds of 'Double dormant' species must spend two consecutive winters in the ground in order
for the seed to break dormancy. These seeds are best planted in the fall, although they typically will
germinate two years after being seeded in the spring.
Hot water is used for species that require heat to stimulate germination. Scarify the seed and then place
it in a bowl. Pour boiling water over the seed and allow the water to cool. This mimics the effects of a prairie fire.
Pour off the water, collect the seed, and then Moist Stratify for 30 days as per directions above.
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