The area under trees in my yard is devoid of lawn. At first I thought it had something to do with lack of moisture or light, then I noticed little clumps or piles of soil all over the bare area. I think they are too regular looking to be accidental. See attached.
Any idea what this is, and whether or not it is something I can fix.
Your first instinct was correct. The piles of soil are worm castings and have nothing to do with your bare lawn. They merely are visible because the lawn is bare. Normally, in a thick turf they would not be noticed.
Turf goes not grow in deep shade, and especially not in dry deep shade. Perhaps you can prune up your trees, or remove some, to get more light in. As trees grow, the lawn beneath gets shadier. This is a common problem a few years after planting a landscape.
Here is some good advice about shade lawns: http://extension.umd.edu/hgic/shade-lawns
If you decide to put ground cover in some areas, avoid English ivy and wintercreeper. Both are foreign invasive plants in Maryland and seed themselves into our parks and natural areas.
Fall is the BEST time to seed lawns.
Thanks. Very helpful...I will trim back the trees to let in more light. Which of the turfs mentioned (hard fescue, creeping red fescue, and sheep fescue) would be the best choice for a Maryland lawn?
The hard fescue and sheep fescue would be the better choices for a Maryland lawn. The red fescue tends to be more susceptible to diseases here.