Yellow leaves are a sign of overwatering impatiens, as is a wilting plant. Your natural reaction to a wilting plant is likely to be to water it, of course, but soil that’s too wet can suffocate the plant roots. The overmoist soil causes the root rot that means nutrients aren’t being absorbed with yellow leaves the result, while the plant wilts and eventually dies. If the stems become squishy and the roots look brown and mushy, the best course of action is to replace impatiens.