For the past 10 plus years, I have had a very healthy bed of mondo grass by the sidewalk at our house. In the last 3 years or so, it has slowly started to thin and become yellow and generally seems to be declining. Both the plants and roots have become small. There haven't been many changes, other than a few trees across the street that have come down which may cause the bed to receive a little more sun. It is east-facing, so in the afternoon it is still protected.
Recently I purchased plants to fill out the thin areas of the beds and try and make
the area look better. When I dug down, I noticed there were lots of tree roots below the bed, possibly from
a nearby laurel oak. Could it be that they have encroached and are taking nutrients away? You can
see that around the sprinkler heads the grass is still lush.
What to do? It is very frustrating!