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What Is Winter Sowing?
The term "winter sowing" generally involves planting seeds in clear or semi clear containers (most commonly used is milk jugs) early in the spring (often February or March) and leaving them outdoors until it's time to transplant them. Winter sown plants stay outdoors through frost, snow, and cold. The container works as a sort of mini greenhouse, protecting plants from wind and causing them to germinate sooner.
The winter sowing method works best with cold tolerant plants. See below for a list of the best seeds for winter sowing.
Why Use The Winter Sowing Method?
There are many benefits to winter sowing seeds. Winter sowing has become more and more popular in the gardening scene over the past few years for a number of reasons:
Winter sowing doesn't require any extra equipment like grow lights, heat mats, or fans
Winter sown seedlings require very little care
Pests and disease tend to be less of an issue in winter sown plants
Winter sown seedlings don't need to be hardened off
Winter sown seedlings tend to be strong and heathy
No indoors space is required to start seedlings using the winter sowing method (Your spouse may be especially appreciative!)
Check out this video on winter sowing by my friend Deanne from Four Sons Homestead.
The Best Seeds For Winter Sowing
The best seeds for winter sowing are seeds from plants that have some tolerance to frost. Here is a list of flower and vegetable seeds that can be started outdoors using the winter sowing method.
Cold tolerant flowers for winter sowing include:
Asters
Bells of Ireland
Calendula
Cosmos
Dianthus
Foxglove
Iceland Poppies (these do not always transplant well but tolerate cold well)
Nicotiana
Pansies
Rudbeckia
Snapdragons
Stocks
Sweet Peas
Violas
Zinnias
Nearly any perennial seeds for your area can be winter sown.
Cold tolerant herbs and vegetables for winter sowing include:
Arugula
Beet (Root vegetables tend to not transplant well but if you are growing for early beet tops, winter sowing works well.)
Bok choy
Broccoli
Brussel sprouts
Cabbage
Cauliflower
Dill
Green or Bunching Onions
Kale
Lettuce (Depending on the variety. Miners lettuce or claytonia is especially cold tolerant.)
Mint
Oregano
Parsley
Peas (Keep in mind these will quickly outgrow the container. Although quite cold tolerant, I prefer to plant my peas directly into the garden were they have more space to grow.
Radishes
Sage
Swiss Chard
Although some say it works, I don't suggest planting sensitive, heat loving plants such as tomatoes, peppers, squash, cucumbers, or basil using the winter sowing method. Even a light frost can be enough to kill these plants.
Containers for Winter Sowing
When choosing a container for winter sowing choose a clear or semi clear container with a removable lid on the top. You will need to cut through the plastic so don't choose containers where the plastic is stronger than your knife or scissors. By far the most common container for winter sowing is the gallon milk jug. It has a small top, trapping heat inside it, and is easy to cut.
Before cutting into your container for winter sowing drill holes in the base of it for drainage. Place a 1/4 inch hole approximately every 2 inches. If you don't have a drill you can carefully make holes with a knife or scissors.
Your winter sowing container also needs some sort of vent in the top to allow for some air circulation. If it has a removable lid remove this. If it is a container without a lid manually place some sort of hole, or vent, into the top. This hole can also be used to water the container if it gets too dry.
Once you have your drainage holes in your container, cut around the base of it at about 3 inches high leaving 1.5 to 2 inches connected to act as a hinge. Fill the base with soil and moisten the soil with water to prepare it for planting.
When to Plant Seeds for Winter Sowing
The idea with winter sowing seeds is to create an environment similar to seeds that survive the winter outdoors and germinate on their own when the time is right in the spring. It is really amazing how seeds that spend the winter outdoors know when it is safe to sprout.
You want to get your winter sown containers outdoors in time that they will experience some of the freezing temperatures of winter. For winter sowing in zone 3 or 4, ideally plant your containers anywhere from late January to early March, but winter sowing can be done anytime prior to your last frost date.
How to Plant Seeds For Winter Sowing
Planting seeds for winter sowing is just like planting any other seeds. You may want to sprinkle seeds across the soil if they are tiny. If the seeds are large enough to handle easily space them 1 to 2 inches apart.
Tip: When working with small seeds I like to sprinkle or place them on top of the soil and then add a thin layer of soil, rather than trying to push the seeds down into the soil.
After planting your seeds, water them in. Make sure you label your seeds as you plant so you don't lose track of what you are growing! If you are writing on the outside of the container use a garden maker or an acrylic marker. Sharpies tend to fade in the sun and are not suitable for labeling the outside of the container. You can also place labels inside the container. Either way works as long as you are using a good quality permanent marker.
Once you are finished planting, dry off your containers and wrap duct tape around the seam to keep the container closed and sealed through any winds.
Placement and Care for Winter Sown Containers
Place your winter sown jugs in an area where they won't be knocked over by wind but will receive sunlight and snow or rain. If temperatures do fall, it is better if the containers are covered in snow as this actually provides some insulation. Remember, we are mimicking nature, we want the seeds to experience the freezing temperature so that they can sense when spring weather starts to warm and when they should germinate.
If you end up planting later in March, place the winter sown containers near a north or east wall for two weeks so that they don't germinate too quickly and die when it freezes.
I am winter sowing in the Calgary, Alberta area and we experience warm chinooks during the winter. If you have the same issue, it may be necessary to move the containers out of the sun for the duration of the chinook as it may trigger germination too early.
Watering Winter Sown Seeds
Water your winter sown containers as needed. If the container feels light or if there is no longer any noticeable condensation inside the container it is time to water. You can water winter sown containers from the vent hole in the top, tilting the container so water can reach the full surface of the soil. You can also bottom water your winter sown seedlings by placing your container in a pan of water 3 inches deep and leaving it there for 20 minutes to absorb the water.
Caring for your Winter Sown Containers
Once you seeds have germinated (sprouted) they can continue to grow in the containers until it's time to transplant them. If the containers were in an east or north exposure, try moving them to a south or west wall after germination so that they will receive adequate sunlight.
Keep an eye on daytime temperatures as the days get warmer. If it gets above 23°C (73°F) open up your containers so you don't "cook" your plants. Close them up at the end of the day if you are expecting frost.
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