Ask Mr. Smarty Plants

As you can see from this USDA Plant Profile Map, Lupinus texensis (Texas bluebonnet) grows naturally in Denton and Tarrant Counties,so we are betting the dirt where you are would work just fine. We believe your area could be considered the Cross Timbers and Prairies. We used to garden there, and we can tell you, there is a very confusing mix of soils in that area. Here is the description from our webpage on the Texas Bluebonnet of the soils in which it will grow:

"Limestone/chalky, Sandy Loam, Limestone-based, Calcareous, Sandy, Medium Loam, Clay Loam, Clay, Caliche"

We agree with the statement made by our Director of Horticulture that the bluebonnet neither requires nor likes rich soils, which is probably why it does so well in Texas. This means that buying potting soil at the nursery for your containers of bluebonnets is going to be counter-productive. We are guessing that at least some of your soil is clay, which can mean poor drainage, so we suggest you mix up your own potting soil. Dig enough out of the ground to fill however many pots you plan to use. Mix in some decomposed granite, sand, even compost to improve the drainage in the pot. And don't fertilize, native plants don't need fertilizer because they are accustomed to the climate and dirt in which they already grow. Then, read our How-To Articles: How to Articles How to Grow Bluebonnets and Container Gardening with Native Plants.