{5 minute read}
Starting a garden from seed is a fantastic way to enhance your gardening skills while keeping costs low. Native annual and perennial seeds, however, require a bit more attention due to their natural adaptations that prevent them from sprouting at the wrong time. To help them germinate successfully, you’ll need to break this dormancy through a process called stratification. This process involves a simple pretreatment that mimics nature’s winter conditions.
Stratification helps seeds break dormancy. By softening the seed coat, it allows moisture to reach the embryo and kickstart germination. This technique lets gardeners start seeds indoors before the weather warms up and allows professional nurseries to grow plants ahead of schedule for a jumpstart in spring. I always encourage home gardeners to try stratification—it’s a fun, rewarding challenge, and there’s something extra satisfying about being able to say, “I grew this from seed!”
There are different types of stratification, and each type of seed will have its own specific requirements. A good seed supplier will provide this information right on the packet. Two of my favorites are Missouri Wildflower Nursery and Prairie Moon Nursery. Missouri Wildflower, based near Jefferson City, offers seeds that are local to our area. By buying from them, you’re supporting a regional small business and getting seeds that are collected from wild native plants. Prairie Moon, located in Winona, Minnesota, also provides native seeds, though they may not be as specifically adapted to our region. While some purists recommend only buying seeds from your immediate area, I like having a bit more flexibility and a broader selection. In my experience, both suppliers offer similar germination rates and plant success. Prairie Moon has really refined their packaging, stratification codes, and instructions—I’m a bit of a nerd about how well they communicate everything. Missouri Wildflower, being a smaller operation, keeps their instructions clear and to the point, which I really appreciate.
There are three main types of stratification: cold, alternating, and cold/moist. While each seed type has its own specific needs, we’ll focus on the first two and dive deeper into the third.
Cold Stratification (CS)
Cold stratification, also known as dry stratification, is one of the easiest methods! Seeds that need CS only require a period of low temperatures to soften their seed coat. I simply place my seed packets in the refrigerator—just make sure they don’t freeze. Temperatures between 33-41°F for one to three months is all that’s needed to break dormancy. I like to store mine in the middle of the fridge to avoid temperature fluctuations that happen in the door shelves. Once the chilling period is over, sow your seeds in flats and place them outdoors (once the weather is suitable) or under artificial light indoors to germinate.
Alternating Stratification (AS)
Alternating Stratification (AS) is a straightforward but slightly more complex technique. Some seeds have evolved to need multiple seasons of dormancy to germinate, requiring a cycle of cold, warmth, and then cold again. To mimic this natural process, you can alternate between placing your seed packets in the fridge (cold) and in a warm spot, like your pantry, to simulate the necessary temperature shifts.
Cold/Moist Stratification (CMS)
Cold/Moist Stratification (CMS) is the most common method for seeds we work with at Pollen to Petal. It mimics the cold and damp winter conditions of our Midwest climate. CMS can be done either in the fridge or outdoors.
The Refrigerator and Paper Towel Method is a popular indoor approach for CMS. Simply dampen a paper towel, place it in a ziplock bag, add your seeds, and store it in the fridge. While this method works well, I don’t prefer it because it takes up valuable fridge space and the seed roots sometimes get tangled in the towel, making the transfer to soil tricky. Some gardeners suggest turning the bag upside down to keep the towel above the seeds, preventing this issue.
For Outdoor Cold/Moist Stratification, the Milk Jug Method is a favorite! It’s a sustainable way to reuse plastics that might otherwise go to the landfill. You can use milk jugs, juice bottles, or even containers from rotisserie chicken or fruit. At Pollen to Petal, we use nursery flats and humidity domes for better organization in our indoor greenhouse. These flats are sanitized and reused to minimize waste. You could use any similar container that provides 2-3 inches of soil depth and 3-4 inches of space for the seeds to sprout.
To use milk jugs or juice bottles, cut three sides of the container to create a flap lid that makes it easy to add substrate, seeds, and check on the germination. Fill the bottom with 2-3 inches of lightly hydrated soil. The soil should hold its shape when squeezed, but not release water. Gently tamp it down without compacting it too much, as the roots need space to grow. Sow the seeds on the surface—most native seeds don’t need to be buried deeply—and top with vermiculite. Lightly water, but be careful not to overwater and drown the seeds. Don’t forget to label your containers!
Now, place your containers outside for the winter! I like to put ours against the concrete foundation of our house or in a raised bed with fall leaf litter for slight insulation. This keeps the seeds cold but not frozen. Some gardeners use a blanket over their containers during freezing conditions.
Be sure to check your CMS containers occasionally. If it’s too dry, water them gently. If the temperature rises unexpectedly, open the lid slightly to prevent the seeds from getting too warm.
Next up, we’ll cover what to do when you bring your CMS trays inside for early germination. Stay tuned, fellow nature lovers!
Photo by u/showtime316
*Pollen to Petal is not affiliated with, nor receives any compensation from any link or company mentioned within this post*