Winter Sowing Seeds in a Cold Climate (Zone 3)

Winter Sowing Seeds in a Cold Climate (Zone 3). Winter sowing is a way to start seeds outdoors in a small container greenhouse while it is still winter. Since the most common containers are used milk jugs, it is also sometimes referred to as milk jug sowing. It was first invented by Trudi Davidoff. It sounds so good that one wonders if it can be true. You will never know if you do not try it, so we did.

I did not doubt the system; it sure sounds possible. Seeds will germinate whenever it is natural for them, and we can trust Mother Nature. In zone 3, however, that time might come way too late since winter in a cold climate does not have good candidates for seed germination. Still, we did try it out hardcore, and here are our first results.

This blog post includes detailed instructions about winter sowing in Zone 3. Our experience has also shown that using winter sowing in combination with indoor outdoor or a greenhouse works even better in a cold climate. In our short growing season, we want to start with vigorous seedlings on time to get the best results.

Zone 3 refers to the plant hardiness zone in our area, where winter temperatures can reach -40 degrees.

Why use winter sowing to start seeds

Winter sowing is a great way to start seeds without a growing room, grow lights, or greenhouse. If your indoor conditions are not optimal for seed starting, consider winter sowing.

We use recycled plastic containers (gallon jugs) for winter sowing, reducing seed start costs. It is a great method for gardening on a budget.

Winter sowing makes seed starting easy, requires less care, and requires less work to harden off plants. However, some care and hardening are also needed here.

Winter sowing is especially good for seeds that need a cold stratification time. For perennial flowers, native perennials, and cold, hardy annuals. If you do it right, winter sowing produces more robust seedlings.

What seeds to start in winter sowing

Winter sowing does not have any magic to it. What we do here is create a somehow sheltered environment to let seeds germinate whenever the conditions for that seed are right.

So, if a plant variety germinates under cooler conditions, that seed will germinate earlier. If a plant variety needs warm soil, that seed will germinate later.

In our experience in a cold climate, only cold-hardy seeds germinate in time to make it worth it. The little container greenhouse is not able to create an environment for heat-loving plants if the outdoor temperature is too cold.

Winter sow perennials, native plants, hardy greens like kale and Swiss chard, and cabbage family plants. A good rule of thumb is that early spring outdoor planting can be started in winter sowing for whatever seeds the seed packet suggests. Tender annuals can also be planted, but here, it is advised to start later and use a combination with other systems like a cold frame or greenhouse. We talk about that more later.

Onions are a great combination crop to start with winter sowing. They require warm temperatures for germination but cooler temperatures for growth. Learn more about winter sowing onions here. 

Even tomatoes do well in winter sowing if they are kept indoors for germination and brought in during cold spells. 

When to start seeds in winter sowing in zone 3

The whole idea of winter sowing is that it can be done in the middle of winter and will work. This is true for a tempered climate. Any seed that would naturally survive being frozen and then germinate would work for winter sowing in Zone 3, also.

We have all seen hollyhocks, dill, cilantro, and other plants emerge in spring after a long, cold winter. Winter sowing is the same idea, just more controlled. Since we create a small microclimate, the seeds will emerge a bit earlier.

That said, -40 degrees is hard on the containers and may damage some seeds. There is no need to expose them to it. The seeds will not come up any earlier if we start them in winter sowing earlier (around the winter solstice). They will come up when the soil reaches the minimum temperature required for the types of seeds planted.

We wait until early March, which is plenty of time. Mid- to late February is a good time to start hardy perennials.

In winter sowing, we are aiming for young, healthy seedlings. For the most part, in zone 3, it seems to be a good idea to go with the same seed starting schedule we use for indoor seed starting. You can find a free printable schedule here.

Prepare the Milk Jag container greenhouse

Translucent containers, such as one-gallon milk and water jugs or vinegar jugs, can be used for winter sowing. However, any container can be used as long as it has drainage holes and an opening for ventilation. The recycled containers must also be clean.

In our example, we used plastic milk jugs. Make 10-12 holes at the bottom and lower sides in a clean container for drainage.

Now cut the jug just below the handle, leaving 1-2 inches by the handle to close and open the top. You want to have enough room for the roots to grow.

Soil for Winter sowing 

Fill the container with light, well-draining soil. Do not use seed starter soil, as it usually lacks nutrients. Instead, choose a potting mix that contains fertilizer. For example, you can use Promix organic vegetable and herb mix soil to start seeds.

If you use a soil mix without fertilizer (read the labels), add compost about 1/3 by volume. This is important because, unlike with indoor seed starting, we will not regularly transplant or water the seedlings. The seedlings need nutrients to grow on their own.

Water the soil throughout and let it drain. You are ready to plant now.

Planting the container greenhouse

Plant the seeds as usual, reading the label of the seed package. Most seeds need to be planted about three times their size deep.

If using very small seeds, sprinkle them on top and cover them lightly with some soil. Push the soil down lightly to ensure the seeds are in contact with the soil.

Do not overplant. Remember that these seedlings will be in the container until you plant them in the garden. Generally, they will be smaller than your usual seedlings started indoors. However, they still need some space to grow healthy roots.

Label the container so you know what is inside. Labeling inside the container also seems to work well since the outer surface will be exposed to the elements. Use a permanent marker that will last.

After planting, close the jugs and seal them with duct tape. We want to keep all the moisture in and prevent wind or airflow in the container. Only the lid is left open.

Bring the winter sowing container outside

Now, it is time for the winter part of the sowing system. In our first experiment, we placed the containers on the south side of our house. A few days later, we got snow, more snow, and heavy frost—too cold for my liking. But I wanted to try winter sowing in zone 3, so we did not pamper the seedlings.

I also had all the containers in a water-tight box, which I would not recommend.

Instead, bring the containers out into the garden to a snowy location. If you can, give them a sunny but somewhat sheltered location from the wind. Place them into the snow so the snow gives some temperature stability and insulation.

If there is no snow and the night and day temperatures fluctuate, you can either cover the containers for the night with a protective blanket or bring them in. This will help speed up germination and protect young seedlings. Protecting them is a must, especially if you are trying to start warm-weather seeds.

Frankie-Lou Fuller, who loves winter sowing in zone 3, has another great tip for a no-snow situation: Make a protective wall around the container greenhouses, using containers that are filled halfway with water. This helps keep the temperature somewhat more stable, prevents overheating during the day, and keeps the plants from being totally exposed at night. 

Again, for seeds that need warmth for germination, like onions or all summer crops, it is advisable to keep the jars indoors after planting. The jars do not need light, just warm temperatures. Once they germinate, get them used to the outdoors. Bring in summer crops during cold spells. Read more about starting seeds without grow lights here. 

Seedlings care in winter sowing

Once the seedlings are up and growing, they will need some care. Now, in my first trial, I did not do anything except rescue them a couple of times from drowning. If you do not keep them in a trey, that will not happen.

As the seedlings grow, they will need water. You will know if they need water by lifting the containers. A dry container will feel very light.

Water from below by placing the jugs into a tray with water. They will soak up the water.

The winter-sowed seedlings will be pretty hardy, but if you are growing a frost-sensitive plant and a sudden deep freeze is imminent, you should bring them indoors.

Note, that protection is not needed for hardy seeds before the seeds germinate. It would only mess up the natural timing for germination (the whole idea behind winter sowing). If we get a spring blizzard, that’s when we want to step in. 

Moving the containers in and out during unusual cold spells will help ensure more constant growth. If you have a greenhouse, keeping the seedlings in it overnight or in bad weather is a great way to combine winter sowing with greenhouse growing.

Later in the season, overheating might be an issue on sunny days. Spring sun can be very intense. After the snow has melted, a location with some protection from the afternoon sun is a good idea for the growing seedlings. In a greenhouse, the containers can be opened later in the season.

Hardening off plants in winter sowing

The plants in a milk jug container are not used to direct sunlight or air movement. They might become very weak seedlings if you leave them closed for too long.

About a week before planting seedlings in the garden, open the containers. Start that process in a shady, sheltered location. Slowly introduce them to sunlight and wind. Covering at first with fleece is a good idea. After that, they are ready to be planted and grow into healthy plants. Note that hardy seedlings can be planted out before the last frost date and heat-loving plants after. Find a schedule here. 

The planting out is the same as planting multiple seedlings from one pot. Here are the eight steps.

If you want to learn more about winter gardening, here are some inspiring books:

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