Gardening with Gardner: Winter Sowing

Gardening with Gardner: Winter Sowing

Does a mid-winter thaw have you itching for spring? There’s a way to start seeds and get a jump on the season, even without a greenhouse or tunnel. You don’t even need space indoors!

Early spring gets very busy in the garden. Take advantage of this quiet time and try winter sowing. All you need is a recycled clear or frosted plastic container that will serve as a mini greenhouse.

The snowy winter months are a perfect time to get started. As long as you have at least 8 weeks until your last frost, you’ve got time. For areas with a last frost in mid-May, like in much of the northeast, January, February, and even early March are great times for winter sowing.

What You Need:

    • A deep container with a clear or frosted top (Milk or water jugs are popular, and large salad greens containers work, too.)
    • A knife or blade, and something to poke holes with
    • Some seed starting or potting mix
    • A label or paint marker
    • Some duct tape 
    • Your seeds!
A hand holding an empty milk jug
Time to raid the recycling bin!

Winter sowing in containers lets mother nature guide your seeds to sprout a little earlier than they normally would, thanks to the “greenhouse effect.” The containers also help to keep tiny sprouts protected from critters like squirrels and chipmunks.

How to Start: Prep Your Container

First, select your container, making sure it’s tall enough to hold a few inches of soil, and a few inches of plants. You also want to be sure it has a clear or frosted top to let lots of sunlight in. Their tall size and built in handle make milk jugs a popular choice. One-gallon jugs are most useful, but a half-gallon could work for just a few seedlings.

Remove the cap from your jug, or cut slits in containers with solid lids. This will act as a vent for steam on warm days (remember, you’re using the greenhouse effect!) and prevent you from cooking your little broccoli sprouts, while also allowing some moisture in. You can use the cap as a label inside, if desired.

If using a milk jug, cut around it just below the handle, leaving the area near the handle connected to act as a hinge. The bottom half will serve as your seed tray. Then, make 4-6 evenly spaced holes in the bottom of the jug. These will allow drainage and help avoid soggy soil. You can poke through with a screwdriver, cut with a blade, or even heat up a hot glue gun to melt a few holes.

Diagram of a winter sowing jug
Image credit: Hudson Valley Seed Co.

What to Grow

First, you may be wondering what types of things you can grow in a milk jug in the middle of winter. The best options are things that don’t mind the cooler weather. Winter sowing is a great method for seeds that require cold stratification. 

Often, these are seeds for perennials or native wildflowers whose seeds would normally be exposed to the snow and cold. They have a hard coating that helps protect the outer shell from breaking and sprouting too early. We’ve all experienced a mid-winter warm spell and seen a daffodil poke out too early! Winter sowing allows the seed to experience the natural freeze-thaw processes that soften the hard shell, but in a tiny greenhouse that you create.

Good options include many native perennials, cold-tolerant annuals, and spring/fall veggies. Here are some plants to try:

    • Echinacea, delphinium, milkweed and butterfly weed
    • Larkspur, snapdragons, foxgloves, hollyhocks, lupines
    • Lettuce, broccoli, cauliflower, kale, cabbage

Look for phrases on the seed packet like “plant as soon as soil can be worked” or in “early spring.” Avoid winter sowing anything that says it doesn’t like to have its roots disturbed, though (like carrots or radishes), as you’ll need to transplant your seedlings when the weather warms. Also skip plants that really need warm temperatures to do well, or have deep root systems, like peppers, squash, and tomatoes. Late winter or early spring is a better time for tender annuals.

Back of a seed packet with highlighted text: "Stratification hastens germination."
"Stratification" will occur naturally as these seeds sit outdoors in your container.

Add Soil and Seeds

Next, moisten your potting or seed starting mix. It’s best not to use garden soil for this type of seed sowing. You want to be sure the soil is well-draining and weed free. Fill up 2-3 inches of the bottom of the jug. Using a container that’s too shallow can lead to the soil drying out or roots being overcrowded. 

Once your soil is in, sow your seeds according to the packet instructions. Make sure you don’t sprinkle in the whole packet! You may have better germination with your mini greenhouse than you’ve had with other methods, and you want to be sure you give the seedlings room to grow. They’ll be cozy in your jug for a few weeks. 

Give your seeds a final light sprinkling of water. You may want to include a label inside the jug, in case the outside one fades. When you’re ready, close up your container. You can tape the seam with duct tape (or something else weatherproof), to make sure it doesn’t blow open or entice critters. You can use a paint marker to label the container (many “permanent” markers will fade in the sun), and then it’s ready! 

Infographic with winter sowing instructions

Let Mother Nature Take Over

Place your container in a bright spot protected from wind that you can access easily. It doesn’t need to be in direct sun all day long, but should get at least 4-6 hours of sun, if possible. In early spring, start to check on it regularly, making sure the soil stays moist and spritzing with a little water if it starts to get dry. As the days start to get a little warmer, you can open the top of the jug during the day and close it at night.

As spring arrives, you can harden off your seedlings, slowly introducing them to full strength sunlight and breezes. Start by opening the jug for a few hours a day, starting in dappled shade, then morning sun, and working up to the growing conditions they require. After about a week, you’ll be ready for transplanting. For best results, make sure your seedlings have two to three sets of true leaves before transplanting them, and choose a cloudy day for the least stress to your new plants.

Winter Sowing is great if you want to get things started without grow lights, seed starting kits, or taking up too much indoor space. Let nature do most of the work during winter and get strong, healthy starts in spring!

A winter sowing container of poppies.
These poppies will stay outdoors and germinate in early spring, safe from squirrels!