Hi Diane, I live in Massachusetts and have always had hostas wherever I've lived. I've always just stuck them in the ground in mostly sun location and watered them as needed. Maybe they need more sun? Not sure why they are turning yellow, sorry :(
I'll bet your sun in Texas is almost as strong as it is here in Florida, and here, for hostas to have a chance, they need to be in full shade. Aim for consistently moist, but not wet, soil.
shade, shade, shade and don't water them as much until you find out if the shade is the solution. too much sun and water is stressful for hostas.