Winter Sowing: Start Seeds Outdoors in Containers

Winter sowing is a way to start seeds outdoors in the cold months, in containers with a clear cover. You sow in winter, leave the containers outside, and the seeds germinate on their own when spring warms. There are no grow lights or heat mats to run, and because the seedlings grow up outdoors, they need little or no hardening off.

What you need

• A clear or translucent container that holds several inches of soil. A gallon milk jug or a clear plastic takeout box with a lid both work.
• Several drainage holes in the bottom, so rain and snowmelt can run through.
• Vent holes or an open top, so rain and snow get in and the container does not overheat on a sunny day.
• Damp potting mix. Garden soil is too heavy for a container.
• Seeds, tape, and a permanent marker for labels. Write the label twice, once inside the container and once outside, because outdoor ink fades.

How to do it

1. Cut a milk jug around the middle, leaving a strip near the handle as a hinge.
2. Punch drainage holes in the bottom and a few vent holes in the top half.
3. Fill the bottom with several inches of damp potting mix.
4. Sow the seeds at the depth on the packet, press them in lightly and label the jug.
5. Tape the jug shut, leave the cap off, and set it outdoors where it gets sun and rain.
6. Check it now and then. Water only if the mix dries out in a long dry spell, since snow and rain come in through the vents.

What to sow

Start with seeds that handle cold. Many hardy perennials and wildflowers, milkweed among them, need a cold, damp spell before they germinate, called cold stratification. A winter outdoors supplies it. Hardy vegetables suit the method too: kale, broccoli, cabbage, lettuce and spinach. Check the seed packet for any special needs before you sow.

Tomatoes and peppers can be winter sown too, but late, around March or April in cold climates, so the seedlings do not come up into a hard freeze. Many gardeners skip tender crops and start them indoors. The seed starting calendar shows the timing for your zone.

When to sow

Sow once the weather has turned properly cold, so the seeds stay dormant until spring. Many gardeners start after the winter solstice and keep going into March. Where winters rarely freeze, you can sow most cool-season crops straight into the ground, so winter sowing adds less. The winter planting season page shows what has a planting window in each zone.

When the seedlings come up

Seeds sprout as the days lengthen and the weather warms. On sunny days, open the top or prop the lid so the seedlings do not cook. Check the mix every few days in spring wind, since small containers dry fast. When the seedlings are a few inches tall, with true leaves, and the soil is workable, plant them out. Hardy crops can go out before your last frost, and tender ones go out after it. If the containers stayed closed, give the seedlings a few days outdoors with the top off first.