Preparing one-gallon plastic jugs
Using a drill, hammer and nail, or soldering iron make holes in the bottom of the jug for drainage. You can also use a small screwdriver heated on your stove burner to melt the holes, but the fumes aren’t healthy.
Using a sharp knife or scissors, cut the jug almost all the way around just below the level of the handle. You want to leave a ‘hinge’ of plastic to hold everything together.
Alternatively, you can cut 3 sides of a square opening leaving a top flap. With this method, you won't need to tape the opening shut. Just push the flap back down.
Planting the seeds
Add about 1 inch of potting mix and sprinkle your seeds on top. Cover with more potting mix to the planting depth specified on the seed package. (Some seeds, such as Snapdragons, need light to germinate, so don’t cover that type with potting mix at all.) Don't water the potting mix now since we don't want the seeds to sprout until Spring.
Place a label or tag inside the jug so you know what you planted. This is important because labels on the outside will fade completely from the sunlight, and you won't be able to read them.
Close and tape the jug with duct tape. If desired, label the jug on the outside with more duct tape and a permanent marker, or you can write directly on the jug.
After the Winter Equinox (December 21), Place Jugs Outside
Place the jugs outside. Be sure to leave the caps off the jugs, otherwise on sunny days, even in cold weather, it can get too hot inside the jug, and also so that rain and snow can enter. During the coldest part of winter, it is not necessary to water the jugs because the seeds will not sprout yet.
I am in zone 5, so in early March, I move my jugs to a plastic swimming pool so that I can easily water them by adding an inch or two of water to the pool. The potting mix will soak up what moisture is needed through the drainage holes without disturbing the seeds.
At the perfect time for each type of seed, the seedlings will emerge. Water as often as needed when there is no rain. Once the weather is warm enough, the seedlings are big enough, and the garden soil is not too wet, transplant into your garden.
If the weather has gotten very warm before I get around to transplanting, I open the jugs so that the seedlings don't overheat and die. The jugs create a greenhouse effect so that sunlight--even on cool days--can make it very warm for the plants.
If the seedlings are very crowded in the jugs, I will sometimes transplant them to separate containers and place them in my greenhouse until they get large enough--and the weather gets warm enough--to plant them in the garden.
This is my method of winter sowing—there are many other ways.
