We go through a disturbing amount of milk in our house, so I was especially excited when I realized that we could use those empty plastic milk jugs as greenhouses to give our garden a bit of a jump start. This process if often called winter sowing, cold starting, or other similar terms.
Not only is cold starting a great way to get a jump start on the spring to make sure you have vibrant flowers for pollinators and people to enjoy sooner, but it also takes some of the steps out of the seed planting process. Using a greenhouse to start seeds outside takes care of hardening off your seedlings as well as the cold stratification process that many seeds need to germinate in the spring.
Save Your Milk Jugs
This goes for any semi-transparent plastic container that can be sealed off. I use giant buckets (well, they're at least pretty bucket-like) of Cheez-Balls as well as milk jugs. Typically starting in about January I start saving all manner of receptacles for seed starting, but milk jugs and giant snack containers work especially well for the greenhouse process.
Drill a Few Holes for Drainage
Be sure to rinse out your milk jug before you dive into the greenhouse conversion. Drill a few holes in the bottom of your new milk jug greenhouse to allow for drainage. Then, cut a horizontal line around about 85% of your greenhouse, roughly about seven inches high on your milk jug. Stop your cut on either side of the handle so you have a nice little handle to move your milk jug greenhouse around.
Add Soil to Your Greenhouse
Your best bet is to add about three inches of damp seed starting soil to your greenhouse. (I often do a bit more, but three will work just fine if you want to be conservative with your soil.) Plant the seeds as recommended, typically about 1/8"-1/4" down in the soil. For seed paper, I like to put a dusting of about 1/8" of soil on top of the paper.
Seal Your Greenhouse
Once you have your holes, soil, and seeds in place, you're ready to seal your greenhouse with waterproof tape. Try to make the seal as tight as you can to keep out the cold. Leave the top open to let in moisture.
Watch the Weather
If it's going to get too cold outside at night, much lower than say 25 degrees Farenheit, you probably want to move your greenhouses inside or cover them with a warm blanket. And if it gets much hotter than about 50 degrees, you can open up the hinge on your milk jug greenhouse to make sure you don't scorch your baby plants with heat.
Move Your Plant Babies
When your plants have two sets of leaves, it's time to move them to their homes. Carefully transplant the seedlings to their home for the season, making sure to plant them in the right amount of sunlight to give them the best chance to thrive.
