When I discovered winter sowing, it was one of the biggest “aha” moments of my gardening life. I didn’t immediately understand the reasoning behind the method, but after a little research I distilled that its root goal is to allow natural processes to simply happen rather than forcing them. This results in much earlier, healthier plants with less work required.
As gardeners, we’re always trying to mimic nature. Often, especially when starting seeds indoors, we’re forced to recreate conditions that are too complex to really pull off. Winter sowing takes away much of the guesswork and worry that comes with starting seeds indoors, plus it saves a ton of space, money spent on buying plants each spring, and a lot of precious time.
Essentially, winter sowing is planting your seeds in mini-greenhouses (milk jugs or a similar container) and placing them outside for the winter. This allows the seed to genuinely experience the conditions required for germination, and each kind of seed will then decide for itself when the time is right to sprout.
This is obviously not a new concept—plants have been growing themselves successfully this way for millennia—but it’s a novel hybrid method as far as human collaboration is concerned. Winter sowing allows the weather and the seed to dictate most of the timing and care, just like a wild seed, only in a semi-controlled setting to protect against factors like washout and predation. It’s the “set it and forget it” of seed starting and it's perfect for lazy, distracted gardeners like me.
Here in Maine, I start sowing in late December and continue at my leisure into February. Trudi Davidoff, the woman who brought this method to its current popularity, says that any time after the winter equinox is safe in most places. You may have thought your gardening season just ended, but by the time you collect all of the milk jugs in your neighborhood, it’ll be time to start all over again.
What to Do in Winter Gallon jugs have become the posterchild for winter sowing containers, but almost anything in your recycling bin will probably work. I use a combination of gallon jugs, old plastic nursery pots, and plastic tubs from grocery store salad greens. If you’re using gallon jugs, cut around the middle, leaving 1 inch as a hinge. Next, cut drainage holes in the bottom of any container that doesn’t already have them and cut ventilation holes in any container with a top (like the salad greens tubs). For gallon jugs, I poke holes in the bottom for drainage and leave the cap off the top for water and ventilation. Then fill your containers halfway with potting soil or compost if you’ve got it, and top with 1 inch of potting soil. Water these deeply and let the excess liquid drain.
Now we sow, but first, it should be noted that winter sowing is only suited for cold-hardy varieties, and all of your tropical or subtropical treats should still be started indoors. Spread your seeds evenly over the soil surface. Add more than you'd think you should—they can afford to be cozy here. In a 4-inch pot that would normally house a single plant at a commercial greenhouse, I sow a carpet of seeds that are easy to tease apart and transplant out, yielding more than 50 plants per 4-inch pot in many cases. This works best for small-seeded perennials that are more forgiving to crowding. Annuals with larger seeds require a little more space, but you should still sow more than you think you’ll need. Press your seeds firmly into the soil (press, not poke). You don’t want to push them down, but you do want the seed to have full contact with the soil. Sprinkle a thin layer of soil evenly over the seeds. You want the depth to be about the same as the seeds' diameter. Press again, gently.
Labeling is crucial at this step, and I even recommend doubling down by writing directly on your container as well as a label stuck into the soil. The label can be a popsicle stick, a store-bought plant tag, a strip of plastic cut from an old window blind or any other piece of plastic. When it comes to the writing utensil, I’m a devoted user of Listo marking pencils. They write on literally anything and won’t fade with exposure to the elements. A paint pen is second best, and a Sharpie will do in a pinch, but they fade within one season of rain and sun. If you’re using a Sharpie, writing on the bottom of the container can help shelter it from fading.
If you’re using gallon jugs, swing the top closed and secure it with tape. Any container without a lid should be covered with translucent plastic with ventilation holes and secured. Full disclosure: though this would fall outside of the “rules” of winter sowing, I have experimented with leaving my nursery pots uncovered and the only differences I noticed were that the seeds shifted around so they weren’t as evenly spaced and germination occurred a bit later.
Voila. Time to set 'em outside and forget 'em. You’ll want to choose a spot that’s out of the way so they won’t get stepped on, kicked over, or plowed into a snowbank, but not so far out of the way that you’ll forget to check on them when spring rolls around. Choose a place that’s protected from wind and too much direct sun. I put mine on a pallet against the west side of my house. Now we wait for spring.
What to Do in Spring The seeds should stay dormant all winter, go through their stratification process, sprout in the spring, and be big enough to transplant just when the garden soil has warmed up. Stay aware and check your pots for early germination during the rare mid-winter warmup or the early spring thaw. Once you start to see those first little green babies push through the soil, you’ll need to monitor your pots more regularly. You’ll want to enlarge the ventilation holes and occasionally water as the days warm up. You may need to open the tops or move your containers to a shadier, damper place to avoid cooking them in the new spring sun. I like to open the tops of the gallon jugs completely as soon as I see germination to spare myself the constant worry of overheating, and I may put them back on for a really cold night.
Once your plants have two or more sets of true leaves, they should be ready to transplant out into your garden or landscape if the soil is thawed and warmed enough. I’ve found them very forgiving if they stay in the pots longer than intended. I’ve also found winter-sown seedlings much more vigorous before and after transplanting, not suffering from transplant shock nearly as much as plants started indoors. When I tip out the first pot into my hand, I’m always amazed at how well developed the roots are and how sturdy and green the top growth is.
I’ve found so much winter joy, spring success, and food all year from this method, and I’m still pretty new to it. I hope you find those things, too.