Stratifying Perennial Seeds

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This St. Johns Wort was absolutely buzzing with all different types of bees on a visit last summer to Asheville, North Carolina. Their little legs were all so covered in pollen it was a wonder they could fly at all.

I will forever be of the opinion that a little magic is embedded in every seed; each season I am in awe of what can grow from such a tiny speck. Perennial seeds have a magic all their own in that they are not tricked into germinating on a warm winter day. Perennials have two defenses; first, they have a very thick seed hull that must go through several freeze and thaw cycles to have a chance of ever breaking open and germinating; second, they must go through several cold moist cycles until the ground temperature is consistently warm enough to allow the seedling to push up through the soil into a harsher environment. See...magic!

Stratifying perennial seeds can be as simple as planting seeds in the fall to overwinter in garden beds and push up their little surprises in the spring. This is as nature intended and of course, works best with native seeds acclimatized to your zone and native range. Being human of course we sometimes forget to do this or want more control over the process so we don't forget what surprises we planted for ourselves. In this case, we can support perennial seed germination through the process of stratification.

Stratification is a process of "pre-treating seeds in order to simulate natural conditions that seeds would experience in the soil over-winter." Prairie Nursery offers this definition and a PDF Seed Stratification & Propagation Guide on their website with incredibly detailed information about different types of stratification for wildflowers, grasses, and sedges. I found this so valuable I even printed a copy for my reference.

One possible way to stratify your perennial seeds is to store them in cold, dark, dry, and rodent-proof place, this might be your refrigerator, freezer, gardening shed, or garage depending on the seed. This is called dry stratification and supports the increased germination of perennial seeds. It is really simple to do with very little effort.

These are the seeds I sorted in January for stratification in February. The Shasta daisy, blanket flower, and black-eyed Susan seeds I harvested from our garden in Golden before we left. I have since ordered a few more varieties from local seed vendors: milkweed, yellow evening primrose, spilanthes, clary sage, larkspur, and columbines.

I decided to not take up more refrigerator space this year and try a method of moist stratification instead using recycled milk jugs as mini-greenhouses. There are loads of youtube videos and blog posts about this already, so I will let you go down the internet rabbit hole if you need more detail than the following. Simply save 1-gallon milk jugs and then:

  1. Cut them in half leaving just a small connection under the handle,
  2. Poke drainage holes in the bottom and vent holes at the top ( I used a hot glue gun to melt holes),
  3. Add potting soil, 
  4. Add perennial seeds, 
  5. Cover with soil, 
  6. Water and close the "lids" duct-tapping the gap.

Voila, a mini greenhouse full of future perennial seeds!

These mini-greenhouses live on the front porch where I can keep an eye on them, open them on hot days, and close them back up on cold nights once spring arrives. For now, they are closed and get a nightly freeze to support their germination once it warms up. As seedlings begin to sprout, I will post their progress below. Until then, I wish you happy visions of pollinator-attracting perennials dancing through your head!

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