Winter Sowing for Native Plants and Natural Habitat

Winter sowing is a method of plant reproduction, especially for native plants and natural habitat that need an extended amount of time with temperatures below freezing. These plants evolved in harsh northern climates and developed a precise method to ensure successful germination. Their programming requires 30,60,90 days below freezing before they germinate. If they don’t get the right dormant temperatures they will wait another year. Some species even require 2 years of cold dormancy before they germinate. These native seeds can lay dormant for decades in their natural environment and germinate when the conditions are right.

Winter sowing mimics this cold dormancy with a process called seed stratification. In nature, seeds are produced in late summer through late fall. As they are dispersed or scattered, seeds fall to the ground and wait for the right conditions for germination. Seeds need soil, moisture, sunlight, and consistent warmth to germinate, which is why they wait until the danger of frost is past to germinate.

We can provide cold stratification by artificial means. Sowing seeds into containers and then placing them outside in an area out of direct sunlight. This will keep them from heating up too soon, resulting in a premature sprouting followed by killing cold.

Another method of artificial seed stratification is to refrigerate seeds. Native plant nurseries use this method to have tighter control over their production.

A third method to create the conditions needed for successful germination is to plant dormant seed directly into the area that has been prepped for seeds. These seeds will germinate once conditions are favorable. Even with these different strategies, some seeds are later succession species. This means that they won’t germinate until other species have gone before them.

We will focus on the container method. The most popular container is the plastic 1-gallon milk jug, which is very common and performs very well. Here are the steps for a successful winter sowing experience:

1. Thoroughly clean your container. Usually rinsing with water, then washing with soapy water, followed by an additional rinse.

2. Using a permanent marker, write the names of the seeds and any other info you wish, like days to germination, etc. 

3. Cut through 3 sides of the milk jug at 4” above the bottom, leaving a 2” wide strip to act as a hinge. The soil depth is important for holding moisture and root development.

4. Poke drainage holes in the bottom of the container so that the soil doesn’t become waterlogged and suffocate the seedlings or cause fungal issues.  4-6 holes the size of a pencil are all you need. You can use a utility knife or a screwdriver that is heated so you can melt holes in the plastic.

5. Fill the bottom of the container with slightly moist potting soil, lightly pressing down to ensure adequate soil depth.

6. Scatter seeds upon the surface of the soil. If you wish, you can scatter a thin layer of potting soil on top of the seeds.

7. Seal the container with tape and place the cap on the container.

8. Place the container out in the sun and watch closely when the weather warms. Remove the cap so plants won’t get too hot in the sun. When plants are large enough, you can transplant them into larger pots or directly into the ground. Remember, these plants are babies and very delicate and vulnerable, so care is required in handling and transplanting.

I have a friend who dislikes tearing the seedlings apart when removing them from the milk jug, so she uses deep-celled potting trays that contain 50 cells, 5” deep, that have perforations for drainage with clear germination covers. It’s a bit more expensive but eliminates a lot of fussy work.

If you want to go it alone, you can follow these instructions. There are many groups that are having hands-on workshops. There are also numerous YouTube videos that provide excellent guidance.