Winter Sowing seeds in milk jugs, is a great way to start vegetables, perennials, and annuals. Of all the seed starting systems, this is by far the easiest and most budget friendly.
Let’s face it, once the holidays are over, it can feel like spring is a million months away. For us gardeners , this is without a doubt the toughest part of the year. Luckily, I’m an optimist and I can tell you there’s a plus side to the calendar flipping the page to January. It means it’s time to start Winter Sowing in Milk Jugs!
What Is Winter Sowing?
Winter sowing is a very simple concept. You plant seeds in the winter and rely on mother nature to do the rest. When the weather warms in the spring, soil temps will increase and your seeds take the cue from nature that it’s time to germinate.
There are a couple of different Winter Sowing techniques, but by far the most common, and most effective is to sow seeds in some kind of plastic container and set the container outside. Milk jugs are most commonly used.
Benefits of Winter Sowing
Anyone that’s ever tried other methods of seed starting such as Starting Seeds Indoors has probably realized at some point there are problems that come up: Seedlings flopping over, damping off disease, and fungus gnats can all make starting seeds indoors difficult. But winter sowing in milk jugs avoids a lot of these problems and instead has many benefits:
If starting seeds indoors you may have to keep seeds in your refrigerator for several months to give the seeds the correct cold treatment. With winter sowing, seeds naturally get that cold treatment by being left out during the winter.
2. No Hardening Off- For those that have started seeds indoors, or in greenhouses, you are probably aware that hardening off seedlings is a huge pain! Winter sowing eliminates the need to harden off seedlings.
3. Overall Less Labor- With winter sowing there’s so much less labor than other seed starting methods. No worrying about filling trays with water. No setting up lights, fans, or shelves. No bringing seedlings inside during the night and back out during the day. Overall, it’s much less labor.
4. More Space Outside- For most of us, space is more limited inside, than outside our homes. Finding a designated area to start seeds indoors can be challenging.
5. Cost Effective- Generally, winter sowing is less expensive. Starting seeds indoors can require lights, benches, fans, seed trays, and watering equipment. Winter Sowing on the other hand requires very little infrastructure and cost.
6. Stronger Plants- Seedlings grown indoors can be leggy as they tend to stretch towards the light. There’s no replacement for sunlight. Seedlings will be stronger, thicker, and overall healthier if grown in real sunlight vs an artificial setup.
When to Winter Sow
For the most part, winter sowing seeds in milk jugs can be done when you’re certain it’s late enough in the season that seeds will stay dormant until the spring.
Here in the Northeast I wait until January to start winter sowing. At this point I know we are in the middle of winter and things won’t be warming up until the spring. Of course, this changes depending on your location.
Whether your up north, or in a more southern location, the key is to pick a period of winter where you can rely on seedlings remaining dormant until temps start to warm up for good.
How to Winter Sow
1. Choose Material- Technically any kind of plastic container will work. Personally, my favorite is milk jugs. Most milk jugs are translucent and let in the perfect amount of light.
If you use clear plastic, you run the risk of too much heat and humidity inside your container. This usually isn’t a problem in cooler climates, but for those is milder climates you could get some warmer, sunny days in winter or early spring. This can create large temperature fluctuations between the day and night. Seeds run the risk of germinating prematurely and dying with freezing night temps.
Most milk jugs on the other hand will let just the right amount of light in. This will prevent conditions from getting too hot and humid during a stretch of warm, sunny weather, and seeds will remain dormant.
2. Prepare Milk Jugs- The first thing you can do is throw away the cap. The milk jugs will be left outside with no cap on.
Next, cut several drainage holes in the very bottom. You can use a utility knife, or a Philips head screw driver to make the holes. To make it even easier heat the end of the screwdriver.
Next, use a sharp knife to cut around the milk jug, about 4” from the bottom (just below the bottom of the handle). Go almost completely around, but leave about an inch uncut so the milk jug stays connected. This inch will act as a hinge and will let you open and close the milk jug. I usually leave this hinge in the corner where the handle is.
3. Use Potting Mix, Not Soil- Make sure you purchase potting mix, not potting soil! Also stay away from seed starting mixes, or anything with a lot of peat moss.
You want a potting mix that has great drainage. Potting mixes should be soilless and contain perlite and/or vermiculite as well as shredded bark and maybe some other fillers. I usually have great results with Miracle Grow Potting Mix. As a reference, one cubic foot should be enough for about 20 milk jugs filled 3” thick.
Place the potting mix in the bottom section of the milk jug. Add enough so it’s at least 3” thick. Don’t be afraid to work through the potting mix a bit to break up any clumps.
4. Purchase Seeds- This milk jug winter sowing method works for germinating lots of different perennials, annuals, and vegetables, but it doesn’t work for all plants.
The key to determining what plants do best with this method is to look for clues on the seed packet or catalogue. You should see words like ‘cold stratification’, or ‘cold treatment period’. Another common word is ‘Vernilzation’. This is telling you that the seeds do best if subjected to really cold temps for several days, weeks, or months, before sowing.
I love getting as much detail as possible about the seeds I’m growing. That’s why I highly recommend buying from a company like Park Seed. They will send you a catalogue (or online catalogue) with detailed info and will give advice on the best sowing methods for each seed packet.
Just be careful not to get too overwhelmed with all the information and horticultural terminology. Honestly, even if the seed description makes no mention that a cold treatment period is best, it is still likely you’ll have success with this method. Don’t be afraid to experiment, seeds are relatively inexpensive.
Some of my favorite plants that I’ve successfully grown from this winter sowing method are:
- Perennials: Phlox, Rudbeckia, Coneflower, Lupine, Foxglove, Delphinium, Yarrow, Veronica, Blanket Flower, Shasta Daisy, Scabiosa, Coreopsis, Lavendar.
- Annuals: Snapdragon, Marigolds, Morning glory, Zinnia, Nastursium, Allysum,
- Vegetables: Broccoli, Cabbage, Cauliflower, Spinach, Lettuce, Chard, Squash, Zucchini, Cucumbers, Pumpkins, Peppers, tomatoes
5. Sow Seeds- Place your seeds in the soil, or on top of the soil, according to the packet. Some seeds require light to germinate, which means they shouldn’t be covered by the potting mix. Others germinate without light, so those should be sunk in the potting mix a bit.
Generally, for larger seeds you want to push the seed into the soil with your finger about 1/8” deep. For smaller seeds, leave them on the surface but pat down so there is good seed to soil contact.
For larger seeds, I usually sow 9 seeds per milk jug. For smaller seeds, 12-16, and for really small seeds I just do my best to sprinkle them on top of the potting mix as evenly as possible. If I have a crazy amount of germination from over seeding I simply thin out the weaker seedlings in the spring.
6. Labeling- Don’t forget to label each milk jug! You’d be surprised how easy it is to forget what seeds you sowed. To keep things simple I like to use one milk jug per seed variety. Things can get confusing when mixing different seed varieties in the same milk jug. In addition to writing the seed variety on the milk jug, I like to also stick a plant label inside the milk jug.
Here’s a link to my favorite plant labels as well as my go to labeling pen (amazon affiliate) :
7. Water and Tape Shut- Very carefully, water your newly sowed seeds. I recommend using a spray bottle to gently soak the first inch or two of potting mix. Using a watering can could be too strong for this initial watering and it could disrupt the seeds.
Finally, use duct tape to tape shut:
8. Set outside- Once your seeds are sowed, watered, and labeled, it’s time to place outside. Place the milk jugs outside so they are exposed to the elements. Don’t leave them under an overhang. The point is to let rain, snow, and sun get into the milk jugs.
If you’re in a warmer region then leave them under some trees where there is partial sun. This will help protect them against strong sunlight and will moderate temperature inside the milk jugs.
9. Be Patient- At this point most of your work is done for awhile. This is the best part of winter sowing seeds. Mother nature is in charge from here on out.
There shouldn’t be any need to water your seeds unless you have had unseasonably dry, sunny weather. If this is the case then watering with your spray bottle can be beneficial. Don’t take the tape off, just shoot a couple of sprays into the top of the milk jug. That should be plenty of water to create a more humid, moist, atmosphere.
10. Open Milk Jugs- Once your seeds have germinated, remove the duct tape and open them up. At this point water them if the weather is dry. You want to keep the soil moist.
Continue to monitor the weather and temperature. For the most part once I open my milk jugs I leave them open. But if we are getting a cold night where temps are going to drop below freezing I’ll close the milk jugs over night. I’ll do the same if there are heavy winds, heavy rain, or hail forecasted.
In the warmer regions be extra conscience of sunlight. Don’t let your little seedlings bake. Keep them watered and keep them in a location where they are out of direct sunlight in the middle of the day.
11. Transplant Seedlings- When seedlings have become established and have developed their true leaves, it’s time to transplant them.
Carefully, make several cuts along the bottom portion of the milk jug so you can carefully remove the clump of potting soil where the seedlings roots are.
Then, using your hands carefully pull apart each seedling. Be careful and keep the roots in tact. Also keep as much potting mix on the roots as possible. At this point you should be able to transplant your seedlings!
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