Ask Mr. Smarty Plants

Mr. Smarty Plants wouldn't recommend Pennisetum setaceum (fountain grass) since it is a native of Northern Africa and considered invasive by the Plant Conservation Alliance's Alien Plant Working Group.  Additionally, it probably wouldn't work very well in the partial shade of your ash tree since it requires full sun.  You can find plants native to your area that fit your criteria, however, by visiting our Recommended Species page and choosing North Central Texas from the map.  This will give you a list, Texas-North Central Recommended, of more than 100 commercially available native plants for your area.  You can use the NARROW YOUR SEARCH option to choose light, moisture and size requirements.  Here are a few suggestions from that list that would work well under your ash tree:

Wedelia texana (Zexmenia) is a perennial and can be evergreen depending on the winters in your area.  It  has a long bloom time.

Conoclinium coelestinum (Blue mistflower) is a deciduous perennial and does require a moderate amount of moisture.  It spreads to form an attractive ground cover.

Callicarpa americana (American beautyberry) is an understory shrub that will grow well in partial shade.  It is perennial and deciduous but has bright lavender berries that last into the fall and winter.

Here are some other possibilities that don't appear on the list but are native to Tarrant County:

Chasmanthium latifolium (Inland sea oats) is a very attractive clump grass that grows well in shade and part shade.  It is perennial, but its foliage and seeds remain attractive well into winter.  In the spring when the new grass begins to sprout at the base of the old clump, you can then cut off the old foliage.

Thelypteris kunthii (Wood fern) is semi-evergreen and requires some moisture.

Carex cherokeensis (Cherokee sedge) and Carex planostachys (Cedar sedge) are grass-like, evergreen and grow well in part shade.

 Malvaviscus arboreus var. drummondii (Turk's cap or turkscap) is perennial and grows well in shade or part shade. 

Additionally, you can find other recommended native plants for your area from the Cross Timbers Chapter (Parker County) of the Native Plant Society of Texas.

Here are photos of the above plants from our Image Gallery:

Wedelia texana

Conoclinium coelestinum

Callicarpa americana

Chasmanthium latifolium

Thelypteris kunthii

Carex cherokeensis

Carex planostachys

Malvaviscus arboreus var. drummondii