Winter Sowing Native Seeds
Winter sowing is a seed starting method that harnesses the natural cold weather period to initiate the germination process for seeds, offering an easy approach for gardeners looking to propagate native plant species. Here are the steps involved in winter sowing one of my favorites, Asclepias purpuracens, our threatened Purple Milkweed, using clear plastic milk jugs, potting soil, and tape. These same steps may be followed to winter sow all other native plant seeds requiring cold/moist stratification.
Cold moist stratification is a process used to simulate the natural conditions that some seeds require for germination. Many plant species, especially those native to colder climates, have seeds that need a period of cold and moist conditions before they will sprout. This process helps the seeds break dormancy and prepares them for germination when favorable growing conditions return in the spring.
Materials Needed:
Clear Plastic Milk Jug: Choose a gallon-sized, transparent plastic milk jug for its ability to create a microclimate conducive to germination. The plastic must be translucent, for sunlight to get in and heat up the soil and air.
Seeds: Source seeds from reputable suppliers or forage your own, ensuring they are native to your region.
Potting Soil: Choose a well-draining mix suitable for native plants. I like the coast of main line of products. You do not need anything with fertilizer in it.
Scissors or Utility Knife: For cutting the milk jug.
Marker: Use a waterproof marker to label the jug with seed variety and sowing date. A sharpie will not hold through the winter. You need to use an outdoor garden marker.
Duct Tape or Packing Tape: Secure the cut portions of the jug to maintain its structure and keep out critters
Steps to Winter Sow Native Seeds:
Prepare the Milk Jug:
Clean the jug thoroughly to remove residues.
Cut horizontally about 5-6 inches up from the bottom, leaving a small hinge for resealing.
Dispose of the top. You want rainfall to enter.
Establish Drainage Holes:
Create drainage holes in the jug bottom to prevent water accumulation. You can do this most easily with a drill.
Fill with Potting Soil:
Add potting soil to the bottom part of the jug, roughly 5 inches deep, leaving adequate space at the top.
Seed Placement:
Sow native seeds at the recommended depth, ensuring even distribution. I plant them densely, 25-50 per jug.
Label and Secure:
Label the jug with the name of the plant and tape the cut edges securely.
Outdoor Placement:
Position the jug outdoors where it will not be knocked over and WILL receive rainfall.
Monitoring and Watering:
Monitor soil moisture regularly and water as needed starting in April. The semi-enclosed structure helps maintain consistent moisture levels.
Transplant Seedlings:
Once seedlings emerge in spring, and have one set of true leaves, gently transplant them into your garden or larger containers. Milkweed is slow to grow, so I recommend transplanting it to another container where you can monitor it until it’s large enough to transplant and not forget where it is.