Saturday, March 12, 2016

Stratify This

This winter I've proposed a landscape project for Franconia Sculpture Park's program. Materially, the artwork will be made of milkweed, Asclepias species, sourced from the northern tier. I don't want to say too much more about the form this planting will take as the jury is still out. I do, however want to share with you the process for stratifying milkweed seeds. It's an easy and fun thing to do should you want to get a jump on milkweed for your yard. You may, of course, plant seeds in fall and the damp, cold climate will do all the work for you, but what fun is that?

It's important to source your milkweed seeds regionally because they will be best adapted to your climate extremes. My project's seeds were purchased from Prairie Moon Nursery, a Minnesota based native seed company. Like many perennials (plants that come back each year), Milkweed requires a period of cold and damp to break dormancy of its seed. This process is known as stratification. 

First you will need sand. It's possible that any sand will do, but I bought this very fine, washed sand at the big box. The fifty pound paper sack (which leaks all over, keep it outside) was under five dollars and I used only a fraction of it.

You must dampen the sand and the first thing you will notice is how the water percolates through it just as it does at the beach. If you'd rather go to the beach than the box store, I recommend bringing a coffee can with you for your seed stratification needs. 

You'll also need some kind of sealable bag, ziplock type or even a baggie. There shouldn't be any free water in the bag after dropping in the sand. Add the seeds and label. I wrote the start date, how long they should be stratified, and the quantity of seeds. And since it is easy to forget about them, I put an alert on my phone to remind me to check in 28 and 30 days.

Here they are -seven varieties of milkweed ready for the refrigerator. If all goes according to plan, I will be potting these seeds in deep cell trays come late March. Afterward, the trays will go into the greenhouse, ahem, the as yet unbuilt greenhouse leaning against an oak tree in the back yard. All in good time. By May they should be ready to plant in our Monarch Park over the drain field and quite possibly at the sculpture park forty five minutes to our north and east.


  1. Sounds like fun. Milkweed is on my list to add this year for the butterflies.

    Question: do you know if it is possible to start seeds in cells in a cold frame? I don't really have room for a light table inside, so am hoping to hear the soil in my cold frames (it's 60's and 70's here now) and then try some zinnia and veggie seeds in cells in a closed frame. Any suggestions? thanks. webb

    1. Milkweed wants 75-80 degrees for germination. With the early warmth this year and in a protected location you may be successful. I'll probably put mine in a greenhouse since I've not grow room either. Good luck!