Not all milkweed species’ seeds need a cold period to break the dormancy of the seed. But for those that do, we must simulate winter if the seeds aren’t sown naturally outdoors in the fall or your area doesn’t get enough winter weather. 30 days of cold moist stratification is usually recommended.  The longer the better but if you are short on time even 2 weeks will still increase your germination rates more than skipping this step. 

   There are 4 common ways to do this. Experiment with the method that works best for you.  If you are stratifying more than 1 variety, clearly mark each plastic baggie with the species and date.  Multiple marked baggies can then be placed in a larger plastic bag or sealed container to further protect the seeds.

  #1 Cold dry stratification. If you don’t have time to do a cold moist stratification method, this is the easiest way and my experimentation with the germination rates between the dry and moist were just about the same, but the seeds are very dried out and must be soaked for a few days to plump them back up before germinating. Instructions: Place the seeds in the fridge inside a plastic baggie for 1 month or until you are ready to start germinating. When you are ready to germinate them, soak the seeds for 24 – 48 hours in warm water before sowing. If you don’t have a seed heat mat, a coffee thermos works for this, change the water once.

  #2 Cold moist stratification using sand or soil. Instructions: Place the seeds in moistened (not soggy) sand or soil inside a plastic zip lock bag or a sealed container and refrigerate. The dampness will soften the seed coating while the cold breaks the dormancy.  This method most closely mimics nature without the freezing periods. For thicker coated seeds like Heartleaf -Asclepias cordifolia and Wooly Pod – Asclepias eriocarpa I use method #4.

  #3 Cold moist stratification using paper towels. This will be the way most sites encourage the practice. Instructions: Moisten a paper towel and spread the seeds out on it. Mist with water from a spray bottle. Fold and place in a plastic bag and refrigerate 30 days or until you are ready to start germinating.  Mark your baggie with species and date.

#4. Cold moist stratification using perlite. Some milkweed seeds are so thick, like Heartleaf-Asclepias cordifolia and Wooly Pod-Asclepias eriocarpa, that they struggle to get out of the seed coat. This cold moist stratification method works great for them. Instructions: Soak the seeds in warm water for 24 hours. Drain. Place in a small baggie along with 1 tsp. perlite. The perlite holds the extra water but doesn’t fall apart like the paper towels do. It also won’t grow mold. Mark the baggie with species and date. They can stay in this mix for over a year if you don’t need all. I’ve started using this method for all of my seeds that need to be cold stratified. When they are placed onto your starting medium with heat and light, germination is speedy.