Soil test. Find out what is in it.

Could it be that it has tree roots sucking up the moisture, or has one of those trees growing nearby, like black walnut or juniper, where things won't grow around them?

I don't think you can over amend the soil, except that it might make the tree roots grow thicker. That happened to the area in which I used to grow miniature roses, until a Cedar elm tree near by made such a thick mat of roots in the bed that I can hardly get a shovel in there anymore. Thank goodness blue plumbago doesn't seem to mind and does extremely well in the spot.

Or perhaps with the extreme drought we are having in some areas of Texas the soil was just too dry for anything to grow. Even when watered here the dirt will be found to be bone dry a couple of inches under the surface.

I think of amendments as compost, manure, leaves and stuff. If you've added a lot of chemical fertilizers, which are okay in small amounts, there could have been a buildup that would burn roots. Some fresh manures will also burn roots.

How is the drainage? Shade and poor drainage could make it anarobic.

If the drainage is poor, you might put in a french drain or other drainage means. Then aerate the soil and make sure it has enough organic matter and nutrients. Like most things garden, enough but not too much.

If its not drainage, you might

check with the gas co. to see if there is a leak in that area