If your Verbena has yellowing leaves, it is dying! To save it you will need to do some drastic actions. Plant it in a medium pot, make sure the soil is moist, put the plant next to a window, but not in direct sunlight, rather in diffused sunlight, then lightly mist your plant at least a couple times per week. Also do not throw out the leaves that you have plucked from the plant, mix those in with the soil of the new pot. Then time will tell. -Birdy