Looking for a winter gardening activity to relieve some of the stress of your spring gardening schedule? Winter sowing is a technique that takes advantage of natural seasonal cycles. We plant seeds outdoors during winter and let them wait for spring. Better yet, it doesn't require much equipment or time.

What is Winter Sowing, and Why Do It

The definition of winter sowing is pretty straightforward–planting seeds in the winter. Instead of waiting for spring to plant all your seeds, we get some started in the ground or their containers early. Winter sowing is a low-cost method and doesn't take up much space in the house. 

Winter sowing has several advantages. First, it's easy. Typical indoor seed starting requires watering, lights, and frequent attention.  Let the seedlings dry out and you're starting over. Don't provide enough light, and you have leggy, spindly seedlings. Fungus gnats, damping off, or forgetting to harden off seedlings are all problems with standard spring seed-starting efforts. With winter sowing, we adopt a simpler approach. We sow them and then sort of forget about them for a while. When we feel the stir of spring, it's time to check and see what might have popped up. It’s a more hands-off approach that can still yield big results.

You'll need a bag of potting mix, duct tape and a marker, seeds, and some old milk jugs, take-out containers, or other clean jugs. They should be clear enough to let some light through. Let's get sowing!

Cold stratification the natural way

Some plants, or rather, their seeds, need to be exposed to a period of cold called stratification. Until the needed chilly period has been satisfied, the seed won't come out of dormancy. Others are perfectly happy to just wait through the cold until warmer weather triggers them to sprout. While they didn't need stratification, they won't sprout in the freezing temperatures and will pop up when soil temperatures warm in spring. 

For either, winter sowing takes advantage of the natural seasonal progression of temperatures to time seed germination. Instead of stratifying seeds in little baggies in your refrigerator, winter sowing lets Mother Nature do it for us outdoors. 

What plants can be winter sown?

Hardy annuals and perennials that require stratification are good candidates for winter sowing. If the seed packet says to chill the seeds before planting or the plant is self-seeding, it's likely a good winter-sowing choice. Heat-loving summer plants, such as sunflowers, are not suitable. 

But there are no hard and fast rules. If you've had volunteer tomatoes pop up a few weeks into summer, you've inadvertently winter-sown a heat-loving annual. The seeds stayed in the garden over winter and germinated when the conditions were right. 

The general guideline is that almost any perennial native to your area can be winter sown. Other perennials that are hardy in your area are also usually good candidates. Cold-hardy annuals, those that like cooler weather and can tolerate a frost or two, are also good seeds to winter sow. The below lists are by no means exhaustive. If you want to try something not listed, go for it! 

Vegetables

Spinach, chard, kale, broccoli, cauliflower, cabbage, Asian greens, and other cool-season vegetables.

Flowers and herbs

Poppies, butterfly weed, rudbeckia, echinacea, bachelor's buttons, milkweeds, chamomile, yarrow, scabiosa, snapdragons, foxglove, larkspur, monarda, sweet peas, and native ornamental grasses.

When to Winter Sow

For the most part, begin winter sowing once your temperatures are reliably below freezing. After the New Year is a good guideline for most folks in the US. The cold temperatures will keep the seeds from germinating early. If your soil warms up for a long period, the seeds could come out of dormancy and be killed by later freezing temperatures. Wait until winter has set in for good.

Most seeds don't need more than 60 days of cold stratification, and many need less, so this method can be done as late as February in northern areas. Perennials can be winter sown at anytime once the weather is cold enough, but cool-season vegetables and frost-hardy annual flowers should be winter sown in late winter or very early spring. They'll pop up when the sun begins to warm the soil mix inside the jugs.

How to Winter Sow Seeds

There are two basic types of winter sowing: in containers and broadcast directly on the ground. Both work, depending on your conditions and how much you need to plant.

Typically, winter sowing is done in milk jugs (the ones light shines through, not the opaque white ones) or similar containers. However, any container that will hold potting soil, allow light through, and can be sealed up will work. The directions below will refer to the milk jug method.

• Wash all jugs well, and don't throw out the caps; you'll want those, too. If you don't have the cap, you can cover the top with duct tape.
• Cut around three sides of the milk jug about halfway down using scissors or a utility knife. Leave the fourth side to act as a hinge. It should now swing open and shut like an alligator's mouth.
• Poke a few holes in the bottom for drainage and the top for ventilation.
• Fill the container to an inch below the hinge with lightly moistened seed starting or potting mix. Firm it gently.
• Sow the seeds according to their needs, whether on the surface or at depth. 
• Label the jug with the species or variety and the date planted. I label it on both the inside and the outside. 
• Tape the jugs shut and set them in an out-of-the-way spot where they won't get disturbed. It's okay if they get covered in snow over winter, but they should be in the sun in springtime. 

Once seeds have sprouted in your containers, they will need a bit more attention, but still less than indoor seedlings. Make sure the jugs and their seedlings are in a sunny spot protected from the wind. Pop them open and check the soil moisture. You may need to remove the cap or poke a few more holes in the lid to provide ventilation. 

As the temperatures warm up, open the lids during the day and close them at night. Your seedlings will be accustomed to the spring temperatures. They won't need to be hardened off before transplanting, and they won't grow leggy looking for more light, as is common with indoor-started seeds. They'll be ready to go out in the garden or meadow.

For winter-sowing large beds of wildflowers or ornamental grasses, prepare the seedbed in autumn before the ground freezes. When the ground starts to get cold, really cold, sprinkle or broadcast your seeds. Then, cover them with a thin layer of compost, soil, or mulch. If it snows in your area, the snow will help water the seeds in when it melts and protect them from wind and birds. They’ll start to pop up in spring, ready to grow.

Tips for Winter Sowing

• Sow only one variety or species per container. Seedlings can be hard to identify when they're young, and organizing everything by container makes it easier.
• Set a recurring task on your phone's calendar or write it on a wall calendar to remind yourself to check on them. They're fine over winter but can easily dry out or cook in spring with a warm spell. 
• Prick out or transplant seedlings while they are small. Winter-sown seeds can often come up thickly and be difficult to separate once larger.
• If you live in a frost-free area, your winter sowing is really just directly seeding in the garden! Whether in the milk jug or a garden bed, watch the soil moisture–too wet, and the seeds might rot before they sprout. 
• Have fun with it, and keep records to see what worked and what did not. After a few years, your garden journal will be a repository of customized information for what works in your garden.