Winter Sowing With Recycled Milk Cartons

Learn winter sowing the easy way with Duluth Wayforger™ Katie of @FrecklesAndSprouts.

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Enjoying a meal with your own homegrown produce is a real treat! Knowing that the food on your dinner table has zero food miles and is at the height of ripeness and nutrition is something more and more folks are searching for.

With spring fast approaching, you may be thinking of starting your first garden. Does starting seeds intimidate you? Are you concerned about growing your own food without the time, space or funds for grow lights or a greenhouse? Even if you have a grow tent at home or a small greenhouse, you may still benefit from a bit more space. Perhaps this winter sowing method of seed starting is just the solution for you!

What exactly is the winter sowing method?

Essentially, you are utilizing plastic containers that would otherwise end up in a landfill (extra eco-friendly bonus points!) and turning them into mini greenhouses for your plants. All it requires is some good-quality potting soil, translucent plastic containers, duct tape, scissors, a screwdriver (or something similar for adding drainage holes) and – of course – seeds. Once you get them set up, nature takes care of most of the work for you.

It is referred to as the winter sowing method, because you can set up these containers and place them outdoors to be exposed to the elements during the winter or early spring. Since the seeds haven’t sprouted yet, it’s perfectly fine for them to be covered under feet of snow. And you don’t have to worry about birds or rain runoff taking your seeds. 

On the other hand, if you have mild winters or “false springs,” like we do in Northern California, you may want to hold off on sowing seeds until early spring. You wouldn’t want to have tomato seeds sprouting during a warm spell of 70-degree weather in February only to have them freeze during a cold snap in March.

As the temperature fluctuations and the lengthening of daylight take place, the little seeds will be waking up at just the right time. Your plants will grow as nature intended, with a little bit of added warmth and protection. There is no “potting up” required as with traditional methods, no fertilizing, less watering needed, and no “hardening off” period as you’d need for seedlings grown indoors.

Because the seedlings have grown up in a natural environment, they will be stronger and hardier. Most of the time, the seedlings will match or even surpass the growth of plants started indoors earlier than those that sprouted on their own time in the winter sowing containers.

How do I know what seeds can grow using this method?

Many flower and vegetable varieties are suited to this method of growing, though this list will vary depending on your location. Here in the mountains of Northern California, I have had great success growing tomatoes like this. However, those in colder climates may not have enough time for the tomatoes to reach their full maturity using this method. Also, plants that are very sensitive to cold and/or require a long season to produce fruits (i.e., peppers, eggplants and okra) are not suited to this growing style.

Surprisingly, though, many varieties will benefit greatly from experiencing the chill. We gardeners do love a good garden experiment, and this is a great place to start. When in doubt, give it a try, but plan on sowing backups indoors or maybe purchasing transplants from a nursery. Who knows, maybe you’ll be pleasantly surprised!

Now, let’s get started!

Begin by sourcing your containers. Milk, vinegar or juice jugs as well as 2-liter soda bottles are all nice choices. I find that the shallower containers do not work as well since the roots do not have as much room. I also do not like the thinner plastic for this as it tends to be brittle and less insulating.

If you are creative, you can find a lot of things around your house that will work (I’ve even used a cake carrier with a clear plastic lid). Just remember that you will need some ventilation or at least a lid that can be taken off and replaced as needed. You wouldn’t want to use anything that was storing chemicals or cleaning supplies at any point. Amber or green colored plastic would not work since it is designed to inhibit sunlight. And whatever you use, drainage is extremely important.

Now that you have your containers, prepare them by cutting them almost in half – leaving an inch or so as a “hinge” so that the container can be opened and closed. You’ll want to make this cut at least 3 or 4 inches from the bottom, but leaving plenty of room for the plants to grow upward as well. This bottom portion is where the soil and seeds will go.

Next, you will want to add plenty of drainage holes around the underneath of the container. I always add an extra layer of holes around the outside of the container at the very base. That way if anything clogs the holes underneath, there is another way for the extra moisture to escape (I’ve learned this one the hard way).

Now that your container is ready, let’s fill it! You might be reaching for your seed starter mix, but hold off on that! We want to mimic the process of sowing these seeds right in the ground, just with a little extra protection. Garden soil would be too heavy on its own and seed starter doesn’t contain the nutrients that the plants will need as they grow. I recommend a high-quality organic potting soil, such as Fox Farm Ocean Forest.

Fill the container to the top of where you made your horizontal cut, and then water it in. Continue adding soil and watering it until it reaches the top of the bottom portion of the container. This is also a good time to check how well your drainage holes are working. Now you can sow your seeds!

You’ll want to sow your seeds to the depth indicated on your seed packet. Sow generously! Many plants are just fine with being crowded for a bit and then gently separated when it’s time to plant. I’ve grown 5 or more tomato plants in one milk jug before, and they didn’t mind being untangled and transplanted one bit!

Push down gently on the surface after you’ve sown your seeds, to help things stay in place. If you want to add a plant marker at this time, you can. I like to label my containers in at least two different places, because the markers inevitably end up fading and I’m left guessing what variety is growing where.

You’re almost done!

Using your duct tape, close up the cut you made in the container. Don’t forget to label the outside or the bottom of the container as well. I like to use a marker for freezer labels or a paint or grease pen.

Put some thought into where you will keep your containers. In most locations, you will want full sun. But if you live in a very warm climate, you may opt for partial shade since it can get pretty warm on sunny days in those mini greenhouses. You’ll want them somewhere they can hopefully soak up the rain as well, although you can choose to hand water them if necessary.

You want the soil to stay damp, and once those seeds sprout you certainly don’t want them drying out. Just be sure you don’t blast a heavy stream of water directly into the containers or else you’ll disrupt the seed placement or damage the young plants.

Place them somewhere that wind, pets and foot traffic won’t disturb them or knock them over. I prefer to group mine together on a table, since I’ve had problems with pill bugs and small slugs getting into the drainage holes and munching the young seedlings.

When things start to warm up in spring, before the seeds have sprouted, I like to close the lids to create a warm, humid environment. Of course you’ll want to make sure they don’t dry out during this time, but I do not find that this happens very quickly.

Your seeds will love the greenhouse vibe that these containers create, and they will soon sprout. Once the seeds have sprouted, monitor the temperatures. Don’t forget to remove the duct tape and open up your containers so your plant babies can feel the breeze and get some fresh air.

Some gardeners add holes or small windows to the top part of the container for circulation, although I prefer to just open them in the morning and close them back up before nightfall.

When the day comes and it’s time to transplant your seedlings, gently scoop them out, separating them if need be, and plant them right away. You won’t need to carry them in and out of the house to gradually adjust to the sun, wind and temperature fluctuations, AKA the “hardening off” process. They are already familiar with all of the elements happening in the “micro-climate” of their milk carton greenhouse, and are eager to stretch their roots!

While I still have plans to add a large greenhouse to our backyard homestead, I enjoy utilizing this method to reduce the amount of seedlings I have on windowsills indoors. Even with the greenhouse, I may use this method for must-have flowers in my veggie patch such as marigolds, nasturtiums, sweet alyssum and cosmos.

When we do our best to mimic the natural growing process as much as possible, this is when we will have the greatest success. It is my hope that you will find this method exciting and liberating as you learn to grow your own food and taste that sweet flavor of self-sustainability.

Katie's Bio