Moss is often a sign of poor drainage and/or inadequate sunlight. It's often seen overtaking lawns on heavy, compacted, waterlogged, clay soils. If you don't be

Moss is often a sign of poor drainage and/or inadequate sunlight. It's often seen overtaking lawns on heavy, compacted, waterlogged, clay soils. If you don't believe that to be the problem, you might have a soil that's overly acidic. Clay soil is a bear, especially when it's been compacted. I had to deal with it for many years when I lived in LA. There are no fantastic solutions that don't risk making the problem worse than it already is. The best you can do is compost generously, and hope for a slow improvement over time. Do not attempt to till the soil or mix in sand. This can actually make the problem 10x worse, creating a sort of concrete-like substance as the clay and sand particles interlock.