Do bananas ripen when placed near oranges?

If you're trying to make fruits or vegetables ripen faster, put them in a bag and close it, this traps the natural gasses in and speeds the ripening process. Some produce the darkness & warmth that can come from a paper bag also helps. If you're trying to prevent the produce from becoming over-ripe before you use it, keep it exposed to air (not in bags) and separate from ripening produce.