When should you replant your ivy in a new pot?

In general, plants need repotting when their roots begin to come out of the drainage hole in the pot. When you lift the plant from the pot, if the roots are thickly clustered around the outside of the root ball, you probably need to repot. Usually plants that are stressed from having too many roots will show signs of distress, like wilting, yellowing, etc. Some plants, like Christmas cactus, actually seem to like crowded root conditions and won't flower when they are repotted.