Last year when I first moved to my new house I done the flower beds. In one area along my stairway leading up from the sidewalk to the front of the house I had planted a Coreopsis on either side, one yellow and one garnet. Neither came back this year. In place of them I planted carnations where the yellow one was and I planted a real dream Shasta daisy in the area where the garnet coreopsis was. That shasta daisy has died after it seemed like it was doing just fine. I planted another real dream Shasta daisy the same day, from the same nursery in a different location of the flower bed. Could there be something wrong with this specific area of my flower bed where I originally lost the garnet coreopsis? If so what can I add to my soil to make it more safe for flowers? I don't want to keep replacing plants in this area for them to keep dying. All of the surrounding area is doing just fine, it's just this few feet of the flower bed. Please note cats have used my flower beds for litter boxes, and they have deficated in this same area I'm having trouble with, but they just started that this year. I picked up and disposed of all the cat waste and now have repellant laying out that is safe for people, pets and plants. I just don't want to have a bare area in my flower bed forever if I can never plant something there again that will stay alive! I'm hoping there is just something that needs added to the soil in this certain area that will help. I have clay soil by the way, which all of my other plants seem to thrive in. I always add top soil and nutrients in the bottom of the hole before placing the plant in the ground and recovering it with top soil then mulch, and dispose of the clay I dug out of the hole. Any thoughts??? I'm hesitant to replant something else in this area.