What a great site!
I looked through the other questions, and learned a lot about some of my other plants.Thank you! Now my question: I grow my ivies by an urban East window, and they seem quite happy. However, some of the vines in a pot of otherwise healthy vines just shrivel up and die. Please help!
Hmm. There are a number of reasons this might happen. Ivies are sensitive to dry environments, which is certainly the case in most homes. You can raise the humidity surrounding the plants by grouping the pots on top of pebbles in a tray or rimmed baking pan that you keep full of water. Do not let the pots actually sit in the water; ivies like to be watered thoroughly but infrequently, that is, letting the soil almost dry out completely between waterings.
You may also be seeing the result of an infestation of spider mites, the insect to which ivies are most vulnerable. The first sign is the appearance of tiny yellow spots on older leaves near the base of the stems. Later, those leaves turn yellow then brown, shrivelled and dried out. At that point, though, you should be seeing evidence of the webs. Spider mites can be washed off the plant using lukewarm water. For more information on spider mites, see this previous answer to a question about orchids; the advice about the mites applies to your ivies, too.