I would check out hydrangeas and impatients. Not sure what will work in your soil but they might be ok. Impatients will bloom some in shade and from what I have heard some hydranges will work. Just my quessing though.

Ferns are good. That area may be too shady even for hydrangeas. Impatiens are always nice - the white ones especially will brighten up the area. Plants with variegated leaves also make the area seem brighter.

You might check with a reputable tree company about selectively removing some of the tree branches to allow more light into the area.

treasureforu & esh ga:

Thanks for the suggestions! I have seen people on my side of the street use impatiens in shade with success. I'm leaning towards impatiens and vinca in window boxes, ferns and boxwood by the house, hydrangea by the fence and maybe a climbing hydrangea over the front porch.

The moss indicates highly compacted, acid soil and very deep shade. Roots from the maple trees have very likely infested all of the soil, making it very difficult to even drive a shovel into the ground. Gardening in containers is probably your best choice for such an area - even these must be protected from the roots as they will go up into the drainage holes more quickly than you can believe.

Gah! That's what I was afraid of. I had heard that moss indicates poor soil. I think what I will do is a raised parterre garden in the horseshoe area, maybe 3-4 bricks high. Then I can fill in with a mushroom soil/topsoil mix. Those darned maples and their shallow roots! (Actually, they are beautiful in the fall)

Four bricks high = 8 inches; probably deep enough for shallow rooted, shade tolerant annuals, coleus being one example, but I'm sure their are others. Keeping the maple roots out of the new soil is the real problem. There are geotextiles impregnated with copper compounds or other substances designed to repel roots. Putting this down first may keep out the roots, but no guarantees. Maple roots are just incredably agressive.

Yes, coleus and impatiens are sooooo pretty, but they are annuals, right? I like to invest in something that will come back. I have a few mossy areas in my shady, wet yard. It's not poor soil to me- just wet, low, and facing north.
I kinda like a little moss, it seems so natural. However, being in TN, with red clay soil, acidity isn't they problem. Do a little research, try raised beds. It makes a world of difference in what you can plant. Good luck!!!