I just did my winter sowing and thought some of you might like to know how to do it. It is wonderful for tomatoes.
I live in east central Indiana and it's winter here though so far it has been very mild. I worked in the yard today clearing off some of the dead stuff and plan to spend some time out there each day getting some spring yard work done. It is also a great time to start tomato seeds or any other seed that will volunteer or a perennial. I also started some foxglove, super sweet 100 cherry tomatoes (my favorite), some beefheart tomatoes, and some Roma tomatoes.
You will need a 1 - gallon milk jug. Use an exacto (sp?) knife to cut around it beginning on one side of the handle and going around the jug stopping at the handle on the other side. This will leave you a hinge to open it up. Poke some holes in the bottom for drainage and fill it with dirt. Moisten the dirt, sprinkle the seeds on top, and use clear packaging tape to seal your cut and make your little greenhouse. Leave the lid off in order for moisture to get in. I put mine on the south side of the house and put the seed package underneath it so I would remember what seed was in which milk carton. In the spring when everything is right your seeds will germinate. You may need to add some water occasionally. If there is condensation on the inside of your greenhouse there is probably enough moisture but you can water them as there is drainage. Your plants will be hardened off and ready to go when the nights are warm enough and all danger of frost is past. You can open up your greenhouses through the day and close them back up at night on warm sunny days in the spring.
At this time of year you may have to order seeds online or you may have some to play around with and see if you like this method of starting seedlings. Something like a bell pepper would not work because the plants are so tender and seeds do not volunteer and are not a perennial. Many things will work for your little greenhouses. I used a container that a rottisserie (sp?) chicken came in from the store. I used a large jug that I got a bulk amount of dried minced onions in. Vegetable oil containers, the large vinegar containers - use your imagination.
I am always so anxious to get started in the spring and it helps to have some plants already started.