Ask Mr. Smarty Plants

You have two problems with establishing ground covers under the native maple tree. We have no idea which maple you have, so we chose one native to New York, Acer saccharum (sugar maple), as an example.  The first problem is shade from that tree. With its huge leaves, the maple is a very good shade tree, and even understory plants need some amount of sun. Then, when the leaves fall, they cover the ground, shading the groundcovers out even more, and then you have freezing weather. The second problem is the tree itself, defending its turf, if you will. The maple tree is somewhat allelopathic, which means it exudes chemicals to inhibit the growth of other plants competing with the maple for nutrition, light and water. The maple is also known for roots close to the surface and even above the surface of the ground. All tree roots tend to be in the upper 6 to 12 inches of the soil anyway, and they can crack concrete, mess with foundations and certainly compete successfully with wimpy groundcover. What we would recommend is that, instead of trying to promote plants that will probably not survive, no matter what they are, why not mulch to the dripline (outer edge of the foliage) of that maple? It will protect the roots, keeping them cooler in the summer and warmer in the winter, and, as it decomposes, add to the nutrition in the soil, as well as holding moisture in, requiring less watering. A good shredded-bark mulch is our favorite. Granted, it will have to be replaced from time to time, but so far, that's what you've been having to do with your groundcovers, right? We find mulch attractive, and looks much better than straggly, weedy groundcovers.

We usually give a lecture on not using non-native plants, because at the Lady Bird Johnson Wildflower Center we are dedicated to the care and propagation of plants native not only to North America but to the area in which they are being grown. Most of the ones you have tried are non-native, but in this case it really doesn't matter, natives probably wouldn't do any better under that tree.