Seed starting is just about to begin in earnest for the year. In some cases the seeds you might want to grow may require some extra steps to germinate best. Annuals tend to do just fine without much pretreatment but often perennials need a period of cold to break dormancy and begin to germinate. This cold period is called cold stratification. Cold stratification simulates the nature seasonal variations the seeds are used to experiencing.
25 Perennial Plants that Benefit from Cold Stratification
Not all perennials require cold stratification but the plants listed on the table below benefit from periods of cold. There are many techniques to break dormancy with cold stratification. I’ve included four potential ways you can cold stratify your seeds but there are many variations of those methods you can try.
| Plant | Hardiness Zone | Cold Stratification Time |
|---|---|---|
| Milkweed (Asclepias spp.) | 3-9 | 30-60 days |
| Perennial Sweet Peas (Lathyrus odoratus) | 4-9 | 4-6 weeks |
| Black-Eyed Susans (Rudbeckia spp.) | 3-9 | 4-6 weeks |
| Columbines (Aquilegia spp.) | 3-8 | 4-8 weeks |
| Delphiniums (Delphinium spp.) | 3-8 | 6-8 weeks |
| Foxgloves (Digitalis purpurea) | 4-8 | 4-6 weeks |
| Lupines (Lupinus spp.) | 3-8 | 4-6 weeks |
| Lavender (Lavandula spp.) | 5-9 | 4-6 weeks |
| Monkshood (Aconitum spp.) | 3-8 | 4-6 weeks |
| Penstemons (Penstemon spp.) | 4-9 | 4-6 weeks |
| Primroses (Oenothera spp.) | 4-9 | 4-8 weeks |
| Roses (Rosa spp.) | 3-9 | 6-8 weeks (some may not require) |
| Sages (Salvia spp.) | 4-9 | 4-6 weeks |
| Snapdragons (Antirrhinum majus) | 5-9 | 4-6 weeks |
| St. John’s Wort (Hypericum perforatum) | 3-8 | 4-6 weeks |
| Viburnums (Viburnum spp.) | 3-8 | 3-4 months |
| Yarrow (Achillea millefolium) | 3-9 | 4-6 weeks |
| Butterfly Bushes (Buddleia davidii) | 5-9 | 4-6 weeks |
| Balloon Flowers (Platycodon grandiflorus) | 3-8 | 4-6 weeks |
| Clematis (Clematis spp.) | 4-8 | 4-6 weeks (some may not require) |
| Purple coneflower (Echinacea purpurea) | 3-9 | 4-6 weeks |
| New England aster (Symphyotricum novae-angliae) | 3-8 | 4-6 weeks |
| Joe Pye weed (Eupatorium purpureum) | 3-8 | 4-6 weeks |
| Bleeding hearts (Dicentra spectabilis) | 3-8 | 6-8 weeks |
Echinacea
Echinacea will benefit from cold stratification. Alternatively you can direct sow seeds in the fall for spring germination.
Here are 4 Simple Ways to Cold Stratify Seeds
Moist Paper Towels Method
For this method, start by spreading seeds evenly on a damp paper towel. Fold the towel to cover the seeds completely, and place the arrangement in a sealed zip-lock bag. Label the bag with the name and date before refrigerating it for the specified duration, which may vary based on the seed variety. Be vigilant for any signs of mold and mist with water if necessary. This worked very well for me when I cold stratified Japanese maple seeds. They actually began germination in the refrigerator.
Sand or Perlite Mixture Method
To employ the Sand or Perlite Mixture method, combine damp sand or perlite with seeds in a container, maintaining a ratio of 3:1 for sand or perlite to seeds. Label the container and transfer it into a zip-lock bag, refrigerating it for the recommended time. Ensure the mixture remains slightly moist but not overly saturated to promote optimal conditions for seed storage. Larger seeds work well in sphagnum peat moss. How to Grow Ginkgo trees from Seed.
Direct Sowing in Pots Method
In the Direct Sowing in Pots method, sow seeds directly in an outdoor pot or cold frame, covering them with soil. Water the seeds thoroughly and ensure proper drainage to foster a conducive environment. Rely on Mother Nature to provide the necessary natural cold period throughout the winter season. Keep in mind that this method might not be suitable for all climates or plant types. Always protect your trays and pots from animals. Squirrels and chipmunks have voracious appetites and will dig through your pots to get to your seeds.
Ice Cube Tray Method
For the Ice Cube Tray Method, begin by filling ice cube trays halfway with water and freezing it. Once frozen, sprinkle seeds on the ice surface and add more water to cover them. Return the tray to the freezer for the specified duration. While this method offers good moisture control, it requires consistent monitoring to ensure the freezing temperatures necessary for successful seed treatment. When you are ready to plant you can place the cubes in your pots and allow them grow normally.
I will often store seeds in a refrigerator in their original seed packet. This seems to do the trick for cold stratification in most cases for the easier to germinate plants but may not work in all cases.
More on Growing Plants from Seed
How to Save Seeds of Echinacea (Coneflower)
Fall is that time of year when gardeners begin the process of cleaning up the garden but also is the time when we begin to think of next year and saving seeds. One of the my favorite plants is echinacea and I like to save…
How to Grow Southern Magnolias from Seed
The other day while on a shopping trip I sat in the car with my daughters while my wife ran into the store for a few things. In front of our parking space was a magnolia. I doubt it was the full sized magnolia (Magnolia…
How to Extract Seeds from Chaff
Have you ever wondered “How do I separate those tiny seeds from the chaff?” It’s not hard and shouldn’t cost you a dime to remove all those tiny seeds. There are quite a few methods for separating the seeds from the chaff, this is just…
A Few Garden Notes for Fall (Basil, Flowers, and Tomatoes)
As Labor Day has now past the feeling of fall is growing ever stronger. Each day the night comes sooner and lasts longer and as that light fades the plants begin closing down in preparation for the end of the growing season. During this time…
How Heucheras Begin (Starting Heuchera Seeds)
Recently I started some heuchera seeds while we were suffering through the record setting deep cold of the last several weeks. I had to do something garden related to lighten my spirits that were quickly being squashed by the weather’s entrapments and starting some seeds…
Seeds and Where to Find Them
By now you may have received your first seed catalog(s) in the mail. It’s a fun time of the year for gardeners. We get to sift through the pages, read the descriptions designed to entice us, and dream of what we will plant next year….
