Daniel, Too much sun will cause pachysandra to yellow. If the soil is alkaline or you are watering with alkaline water, it could be lack of iron. In this case you might use a chelated ( liquid iron) or the grandulated Ironite according to package directions. You can also give the groundcover a dusting of Espoma Holly-Tone at the recommended rate. Keep in mind fertilizer will not help if it is a sun issue. Best And Happy Yardening, Nancy.