Line the bottom of the cardboard box with black and white newspaper - not glossy and preferably no colored ink. Some folks individually wrap every tomato in newspaper instead of just lining the bottom of the box with it. This step is optional but highly recommended to help speed up the ripening process and to decrease chances of molding.
Place 12 to 24 medium to large green tomatoes in a cardboard box.
Fold the flaps of the cardboard box closed. If necessary, place something with enough weight to make them stay closed but not so heavy that the box is damaged, on top. I recommend against taping the box closed because when you check the ripening progress every few days or replaced a rotting banana, some of the cardboard will be pulled off and could infuse too much air into the box.
Place the box of green tomatoes in a warm but slightly humid place for up to two weeks to ripen.
You can add a second layer of black and white newspaper on top of the tomatoes to create space for a second row of green tomatoes. But, do not add more than two layers or the weight on top can become so heavy that the tomatoes on the lower layers are bruised, or worse yet crushed and ruined. When creating a second layer, use about five to seven sheets of newspaper or a piece of cardboard cut to fit inside the box.
