Gaillardia will come back or reseed well enough in your zone if you allowed your flowers to go to seed. The seed is the round prickly dead bloom. You can easily take one and crush it in fall in the area you want it and it should come in spring. If you dead head there won't be any seed.
Do you have both gaillardia and dianthus in full, all day sun? Both of these plants are made for sun and heat. We have 90-115 degree summers here. They thrive on the higher temps. It's 2 plants I can count on to come back each year. I've had them green when it snows and they survive and come back in spring. I have grown both in fertile soil and Sandy soil and potting soil... I hope this helps. Maybe it's just a simple matter of moving them where they will be happier?
