Question
I have lived in my house for 9 years and have had problems for the last 2 years with bald patches on the lawn in my small back yard. I had not noticed that the trees have gotten a lot larger (and shadier!)until last summer when it dawned on me that there was not enough sun in some spots.  We tried grass seed for "shade" without luck.  Now, after a very wet spring, there seems to be mold on these bald patches. The soil looks black and smells... moldy. I am a complete amateur on lawn and garden topics, so any suggestions would be appreciated.

Answer
Hi Amy, Grass is difficult to grow under trees.  Grasses are sun loving plants.  You don't see them when you walk through the woods.  Some grasses tolerate shade better than others.  Fescue survive because their growing season is reversed from the trees.  It's growing in Sept - May when the trees have no foliage, it's in full sun.  It's slows or is dormant during the heat of the summer, just happens to stay green.
Shade is not you're only problem.  Water competition from the trees and soil compaction is just as detrimental to grass.  The black stuff is probably algae, a sign of compacted soil.  
Loosen the soil on a regular basis, keep you're pH at 6.5 and water deeply when needed and you can grow grass.  But I'd consider groundcovers instead.  It will be easier for you and less maintenance.
If you are determined to grow grass, go see your local independent nurseryman.  He'll start you on a program to have a shady lawn with the right grass and products for your area, not what the big retailers want to sell you.  Jim