Big Blue or giant liriope look great around the base of a shade tree. They become more of a focal point than a groundcover, especially alternated with giant variegated liriope or even regular-sized variegated or green liriope.
If you want to extend the bed, making a wider radius, start with a center circle or two of the giant plants and then surround them with regular liriope or the even smaller mondo grass. Other groundcovers such as Asian jasmine could be used as a contrast to the liriope, but staying with one texture of the grass-like foliage in different sizes is very effective.
Gallon-sized big blue plants are large enough to be eye-catching and fairly easy to fit between tree roots. It helps to prepare the bed by working in some organic matter and then mulching the plants, but liriope are not fussy and can survive in almost any shady spot.
Rosemary Moyers, Smith County Master Gardener
Texas AgriLife Extension Service