Stratifying perennial wildflower seeds

seeds held in the open palms of a white woman; wildflowers can be seen in the background
Many native perennial wildflower seeds need to experience environmental conditions that break their dormancy before they will germinate. Photo credit: Cornell CALS Communications

Did you miss your opportunity to plant perennial wildflower seeds directly in the ground last fall? Don’t despair!

If you happen to have some bare ground prepared but just didn’t plant the seeds, you could wait until late winter and sprinkle seeds on bare soil. This practice is known as frost seeding and is sometimes used on farms to sow cover crop seed. Cycles of freezing and thawing soil help work the seeds into the ground.

If you don’t have bare ground already prepared, or if starting seeds inside sounds more appealing, you can stratify your seeds inside now. January is a great time to do that, at least if you are living in USDA plant hardiness zone 5 or 6.

What is seed stratification?

Stratification is the process of breaking the dormancy of seeds; signaling that they can “wake up” and be ready to germinate. Seed stratification generally requires exposing the seeds to the right amount of moisture and the right temperature for the right length of time. Some examples include:

  • Hot water soak – Pour hot water over seeds and allow them to soak
  • Cold moist stratification – Mix seeds with sterile sand, vermiculite, or another substance that won’t hold too much moisture (e.g., damp paper towel or coffee filter). Make sure that whatever medium you use is only damp and not too wet. Put the mixture in a plastic bag or closed container in your refrigerator for the required amount of time.

Last spring I described the different types of stratification (and scarification) recommended for some of the perennial wildflowers I’ve been growing in central New York. For many of these species, 30-60 days of cold moist stratification is recommended. So, if you start stratifying your seeds now (late January), they’ll be ready to move to a warm (and often well-lit) spot by the end of March. This will give them 6-8 weeks to germinate and grow before you transplant them outside in the spring.

How do I stratify my seeds?

Cold moist stratification – keeping seeds cool and moist for an extended period – works well for many perennial wildflower seeds. That’s the method I use most often. Sometimes multiple stratification methods will work for the same wildflower species. Don’t be afraid to experiment!

Several containers (plastic and glass jars, paper and plastic envelopes) of seeds and a permanent marker laying on a desktop.
Perennial wildflower seeds I collected last fall. Full disclosure, I don’t know if all these species require stratification to germinate.

 

Cold-stratifying seeds at home can be very simple. I’ve been successful with just some paper towels and Ziploc bags. Don’t forget a permanent marker. Future you will appreciate the time you spent labeling your seeds now! I like to write directly on the paper towel in which I will wrap the seeds and include the date.

Paper towels labeled with names of wildflowers and date next to a permanent marker and a plastic Ziploc bag.
Label the paper towels you will use for cold moist stratification. I recommend including the plant species and date.

 

Get the labeled paper towels wet, then squeeze all the excess water out. You want them to be damp but not dripping. Sprinkle seeds into the middle of the paper towel, then wrap the seeds up.

Several damp paper towels on a countertop, each with a small pile of seeds in the middle
Sprinkle perennial wildflower seeds into the middle of each labeled, damp paper towel.

 

Two damp paper towels in different stages of being folded around the seeds
Fold the damp paper towel around the seeds.

 

If the paper towels are folded so that seeds won’t fall out, you can put multiple “packets” of damp paper towels in the same sealable plastic bag. You could also re-use a plastic container. The goal is to seal the moisture in so that the seeds don’t dry out.

Six folded paper towels, each labeled with the name of a different wildflower and a date.
Seeds neatly wrapped in dated, damp paper towels and ready to spend some time in the refrigerator.

 

Now put your bag or container of seeds in your refrigerator. Write a note on your calendar or set a reminder on a digital device to pull the seeds out in 30-60 days, depending on the species. See last spring’s blog post to learn how long to keep different wildflower seeds in the cold before you try to germinate them.

Plastic Ziploc bag filled with folded paper towel packets of seeds on a refrigerator shelf
If you share your refrigerator with family, friends, or co-workers, make sure to label your plastic bag or let them know what you’re up to so that your seeds aren’t accidentally thrown away!

 

Germinating your seeds

When it’s time to take your seeds out of the refrigerator, start by preparing moist (but not too wet) potting mix. Pay attention to whether your seeds need light to germinate (should only be pressed into the surface of the potting mix), or can be buried. Just like your annual flower or vegetable seeds, many – but not all – perennial wildflower seeds also appreciate a warm spot (e.g., on a heat mat) when they are germinating.

 

I’ll let you know how my seed stratification worked. Happy seed-starting!

 

 

This post was written by Amara Dunn-Silver, Biocontrol Specialist with the NYSIPM Program.

 

This work is supported by NYS Departments of Environmental Conservation and Agriculture and Markets.