Green tomatoes begin to ripen if you arrange them in a sturdy box so that none of the tomatoes are touching and place them in a cool, dry place. Tomatoes that are only half-green continue to ripen on the kitchen counter.
Before placing the green tomatoes in a box, wash and dry them thoroughly. This removes bacteria or spores that may cause rot. Line the bottom of the box with a layer of newspaper to catch any moisture. Check the tomatoes every other day and discard any that become soft or begin to rot. Remove half-ripened tomatoes and place them on the kitchen counter. If you keep them between 50 and 65 degrees Fahrenheit, the tomatoes should ripen over a period of three weeks to three months.