Where I live, the snow is rapidly melting, leaving behind a landscape that seems almost barren and asleep. However, for many native plants and quite a few garden perennials, it is this act of freezing and thawing that awakens them and actually increases their ability to survive and reproduce.
Cold stratification is the term used to describe this very basic need; the need for winter. Winter has the ability to soften the outer seed coat of some of nature’s toughest seeds through the action of freezing and thawing in a moist environment. For many plants that require stratification, this process can take up to 2 months and typically occurs between 34 and 41 degrees Fahrenheit.
During that time, the seed coat softens and embryonic growth is stimulated. Eventually, the embryo bursts through the softened coat and begins the process of germination.
For those of us who enjoy starting our own flowers, there are some classic perennials that require a period of cold stratification to increase germination. One example is Echinacea, a personal favorite of mine. Echinacea is a plant gifted with many benefits.
Most home herbalists are aware of its medicinal properties and gardeners love it for its beauty, low maintenance requirements and as a mid to late season nectar source for beneficial insects. For these reasons, Echinacea has a place in nearly every garden and farm. But purchasing mature Echinacea plants from a nursery can be expensive and often some of the most interesting varieties (rare or endangered native prairie Echinacea varieties have only been available in seed form recently) are not available commercially.
For these reasons, I started growing my own Echinacea from seed a number of years ago. In the beginning, I had mixed success. Without a period of cold stratification, the germination rate for this garden beauty can plummet to less than 30 percent. However, with stratification, it is possible to germinate nearly 100 percent of all Echinacea seeds that are started.
Cold is Good
Cold stratification is a process that is easily replicated at home in a controlled environment. After the seed is planted into a good quality potting mix, water thoroughly until the soil is completely saturated but no longer dripping out the bottom drain holes (I like to plant one seed per cell in a 78 cell container). Then, wrap the top of the container in clear plastic wrap and secure it loosely with duct tape. Put a piece of tape on the top of the plastic wrap with a label indicating both the date the seed was planted and the date that you are removing the container from cold stratification. Also include the name of the cultivar that was planted in the container if starting multiple varieties or species at the same time. Place the container onto a cookie sheet or nested in another hole-less tray that will catch any excess moisture and eliminate any dripping or mess.
When all of these steps are complete, slide the tray into a spare refrigerator (like the drink fridge you keep in the garage) and place a note on the outside door of the fridge with the date the seed was started and the date the tray should be removed from cold stratification. Typically, 30 days is enough stratification time for Echinacea.
Other species may take longer. During those 30 days, check on the container about once a week and make sure that the soil is still sufficiently moist. If need be, pull out the container and water thoroughly. This should only need to happen once in the 30 day period since the plastic wrap will help to retain soil moisture.
After the period of stratification has finished, pull the container out from the fridge, remove the plastic wrap and continue the seed starting ritual like usual including any heat mats or lighting that you typically use for your vegetable starts. For ensured success, follow the germination temperature guidelines specified on the seed packet. Temperature can be controlled by adding a thermostat onto your heat mat.
For those of us who like to collect seed heads from plants we already own or from native plants (ex: Balsam Root), an even easier hands-off approach is to take the saved seed (good quality, mature seed heads), plant it into a ½-gallon or similarly sized pot, place the pot in the shade outside your house for the summer and then water the pot intermittently over the fall and allow it to freeze and/or get snowed on over the winter.
Come spring, move the pot into a sunnier location and water regularly without overwatering. Take note of the rate of germination and experiment with overwintering your seeds in different locations around your yard to see if germination increases or decreases with location.
Cold stratification can be a lot of fun! With practice and persistence you will be able to grow more than enough Echinacea for your needs as well as those of your family and friends. Good luck and Happy Gardening.
Eron Drewis co-owner of Tierra Garden Organicsand retreat center manager at Tierra Retreat Center. One of her most recent projects is founding FARMY-Food Army, an organization aimed at offering support to small and start-up farms in North Central Washington and fundraising for a future equipment co-op. If you would like to read more from Eron including essays, past garden-related articles and more, please visit her personal blog, Farmertopia, and find all of her MOTHER EARTH NEWS postshere.
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