Cold Stratification for Planting Spring Seeds: What, Why and How
With the approach of spring and cold winter, gardeners begin to worry about putting those seeds and seedlings in the ground to be ready for a beautiful flower garden or vegetable garden. Last frost dates are noted and research is done on what each type of seed needs to reach its full potential.
What is cold lamination?
Many seeds, especially annuals, can simply be planted in the ground after the last spring frost and have plenty of time to do their thing before the first fall frost rolls around. However, some seeds, especially native perennials, don’t always work that way. In particular, wildflowers that self-seed in late summer need their seeds protected from frost and/or unusual periods of heat that could cause the seeds to germinate too soon. These seeds enter a state of dormancy called cold stratification until they are ready to reappear, in time, in the spring.
Many people have started to see the benefits of grow native wildflowers in their gardens. Growing native wildflowers helps promote local biodiversity and maintain local bird and insect populations. Research has shown that some native trees can support the existence of hundreds of local creatures, while imported non-natives may only support a small handful. Some butterflies are often on the lookout for specific flowers to feed on and lay eggs on, and with the depletion of natural habitats and green spaces, this proves to be a challenge.
In an effort to start giving back to the earth, gardeners, both seasoned and amateur, hunt for seed packets filled with mixed wildflowers, echinacea, milkweed, black-eyed susans or St. John’s wort. With all the good intentions in the world, some seeds will have very low germination success without being subjected to cold stratification. While seeds that fell to earth directly from their parent plant the previous year will naturally experience this cold stratification, seeds from a seed packet will not and will need a little helping hand.
Luckily, this cold lamination process is something that can be replicated fairly easily.
How can I cold stratify my perennial seeds?
If you have perennial wildflower seeds that you want to sprout in the spring, you have two options. You can sow your seeds in early winter, safe in the knowledge that your seeds will endure the depths of cold and will naturally cold stratify. However, if spring is already approaching and your seeds are still in the packet you bought them in, there is a way to force this process.
There are two ways to recreate this process. One is using sand and the other is using a paper towel. The paper towel method is the easiest method because it works for all seed sizes. Some of the smaller seeds will get lost in the sand and it will be impossible to retrieve them.
- Paper towel method: Take a square paper towel and dampen it with a spray bottle of water. You don’t need to saturate the towel, just moisten it. Then, on a quarter of the towel, sprinkle your seeds. Do not go more than one layer deep with your seeds. Fold the paper towel around your seeds so they are wrapped. Put the paper towel in a ziplock bag and label it with the type of seed you have inside and the date. Then place the bag in the fridge for 4-6 weeks.
- sand method: This is a good method for large seeds that can easily be removed from the sand at planting time. Put sand in a jar and spray it with water. The sand should be fully moistened, but not so wet that it clumps in your clenched hand. Next, put a good handful of sand in a ziplock bag and add your seeds. Make sure the seeds are completely covered with sand. Close the bag, label it with the variety of seeds and the date, and put it in the refrigerator for 4 to 6 weeks.
Once the cold stratification process is complete, you can plant the seeds according to the instructions on the seed packet. This process will greatly improve the germination rate of certain varieties of perennials, especially native wildflowers. Use this method, and you will have yourself a beautiful garden that will delight you and the pollinators!
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