Stratifying Seeds the Easy Way

by C. Dodd on January 31st, 2012

Stratification is a method of getting seeds to germinate by providing them with a few weeks of damp, cold conditions.  A lot of native seeds need to be stratified before they will germinate. An easy way to do this is let nature do the work by planting your seeds in pots in February or early March, and then just leaving the pots outside under the snow until spring thaw. The snow will insulate the seeds and will protect them from extreme temperature fluctuations.  

The Method
Plant your seeds in pots using a good potting soil. It's best to plant the separate species in separate pots. It makes them easier to identify once they come up. After the seeds are planted water the pots from the bottom until the soil is nice and damp, and then take them outside and carefully bury the pots in the snow on the north side of the house. Be sure to mark the spot with a flag on a stick so that the pots don't accidentally get shovelled aside. The alternate freezing and thawing cycles do the work of breaking down the tough seed coat, so that after the snow melts in the spring,  the seeds will begin to germinate.
(Bruce Bashforth of Bedrock Seedbank likes to cover his pots in plastic, and bury them in an enclosed container to keep the moisture in. I prefer to put my pots in a shallow tray with no cover. Both methods work well, but it is important to bury the pots in the shadiest spot - the one where the snow melts last in your yard.)

Once the snow has gone, you can bring your pots inside and put them in a sunny windowsill or under lights. Your plants will geminate faster using this method, but they will need more care indoors. An alternative method is to leave  the pots outside in a semi-shaded spot to germinate naturally. Leave your pots uncovered and stand them in a shallow tray so they don't dry out too quickly. This makes it easy to water them from the bottom. However, make sure when it rains that you drain the tray so that the pots are not standing in water. The soil should be damp but not waterlogged for a long a period. Be sure to check every day for moisture levels and signs of germination. The only species that likes drier soil once it has germinated is Prairie Crocus. If you are growing Prairie Crocuses let them dry out between waterings.

Different species germinate at different times. Some will be up in April; most will emerge some time in May, and a few stragglers won't show until June, just when you have given up on them! I find that some species won't germinate until after the first good spring rain. Some species, such as Blue-eyed Grass, will be stubborn and won't germinate at all, but if you bury the pots up to the rim in a sheltered spot in the garden, those plants might pop up the following year. Remember to mark them well and water them occasionally during dry weather.

Planting Details
Large pots, 12 to 15 cm (5 or 6 inches) in diameter are best. This size gives the seedlings enough room. You can use cell pacs instead of pots if you prefer. Cell pacs are useful because you don't have to go through the hassle of separating the tiny seedlings during transplanting, but they do dry out faster.
You will also need a good quality commercial seed starting mix. These are soil-less mixes that contain peat moss. I usually get mine at Apache Seeds, but any garden centre will have it. Make sure the mix is damp before you start. I use the mix because it contains very few weed seeds, and the tiny native seedlings will be easier to recognize when they emerge. This is also the reason that I use a separate pot for each species - it's easier to tell if the emerging seedlings really are the ones you planted if they all look alike.

Fill the pot to about half an inch from the top and gently press the mixture down flat. Sprinkle the seeds over the surface and try your best to space them evenly. This is not an easy thing to do. Remember that a little goes a long way, so don't crowd those seeds! The seedlings will be a lot easier to transplant if they are not packed together in a big clump. If you are worried about poor germination, just plant two pots instead of one. Seeds should be covered
very lightly because a lot of species need light to germinate. Fine seeds, such as harebells, that looks like dust should not be covered at all.

For large seeds, such as Alpine Hedysarum, the general rule is to cover the seed with soil to twice the diameter of the seed. When you are finished, label the pot with 2 labels (it's amazing how many labels go missing), water it from the bottom and let it sit for a while until the surface is nice and wet. Try to use melted snow water, or tap water that has been standing for a day or two so that the chlorine has had a chance to evaporate. Your pots are now ready to go outside.

Bruce Bashforth of Bedrock Seed Bank taught me this method. Thank you Bruce!

Species That Don't Need to be Stratified 
These seeds can be planted in April or May:

Most grass species except for Blue Grama Grass
Alpine Hedysarum (Hedysarum alpinum). Soak the seeds of this species in hot water for 12 hours before planting.
Gaillardia (Gaillardia aristata)    
Giant Hyssop (Agastache foeniculum)
Meadow Blazingstar (Liatris ligulistylis)   
Smooth Fleabane (Erigeron glabellus) 
Wild Bergamot (Monarda fistulosa)  
Wild Blue Flax (Linum lewisii)
Common Tall Sunflower (Helianthus nuttallii)


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