Options for ripening green tomatoes indoors include:
- Placing them on a sunny window sill. This is a hit or miss solution. You’ll have much better luck ripening mature green tomatoes. Although the tomatoes are more stable sitting on their stem side, they will rot less readily if you can place them blossom side down.
- Wrapping individual green tomatoes in newspaper and layering in a box, no more than 2 layers deep. Place the box in a dark, dry spot and check weekly for progress. It usually takes 3-4 weeks for the green tomatoes to ripen, but check frequently and remove any fruits that show signs of rotting.
- Placing the green tomatoes in a paper bag with a ripe apple. The apple gives off ethylene gas, which speeds up ripening. Check the bag daily.