Ask Mr. Smarty Plants

Here is a previous Mr. Smarty Plants answer on some of the things that could cause problems in Melampodium leucanthum (Blackfoot daisy) (as well as another plant). We don't know that any of them apply, but you could at least compare the description of what the plant requires with the conditions in your garden and see if any of the problems apply to your situation.

Beyond that, our first suspicion is your soil type. From this USDA Plant Profile Map, we learned that the Blackfoot Daisy is not even native to Denton County. If you follow the plant link in the first paragraph to our webpage on this plant, you will see these growing conditions:

"Growing Conditions

Water Use: Low
Light Requirement: Sun , Part Shade
Soil Moisture: Dry
Soil pH: Acidic (pH<6.8)
Soil Description: Dry, rocky, calcareous soils. Rocky, Gravelly Sandy, Limestone-based, Caliche type
Conditions Comments: Blackfoot daisy is a sturdy, mounding plant, that will flourish in rock gardens. It is heat and drought tolerant. Good drainage is essential to its success. In late winter, older plants can be cut back halfway to keep them compact. Rich soil and abundant water will likely produce many more flowers in the short-term, but may consequently shorten the lifespan."

None of the soil description sounds like black clay gumbo, does it? This is often referred to as a desert plant and it really does not tolerate water on its roots. Clay soils are very fine particles which catch and hold water, swelling to exclude air, thus trapping roots in more moisture than they like. Also, notice that blackfoot daisy likes part shade (2 to 6 hours of sun a day) as well as full sun (6 hours or more of sun a day.)

Initially planting of the Melampodium leucanthum (Blackfoot daisy) in soil that had been amended with some decomposed granite, sand or even compost would have helped alleviate the effects of the clay. Usually we recommend that perennials be trimmed back in late winter, anyway, so we suggest you trim back all the suspect foliage and give it a chance to start over. We don't think the frosts materially hurt it because you are in USDA Hardiness Zone 8a, and the Blackfoot Daisy can tolerate temperatures lower than that. Spreading a little compost in the area could help because it will decompose down into the soil and help to break up that clay.