There are some options when ripening a green tomato.Place them on a sunny window sill. Wrap individual green tomatoes in newspaper and layer in a box, no more than 2 layers deep. Place the box in a dark, dry spot and check on them weekly for progress. It can take 3-4 weeks for the green tomatoes to ripen. Place the green tomatoes in a paper bag with a ripe apple. The apple will give off ethylene gas, which speeds up ripening. Check daily.