About 4 years ago, I put down 4 inch deep of wood chip mulch (cheapest kind bought at Home Depot), and then 1 inch every year after. I noticed lately, grass and weed have been growing much more than before. I suspect that the 4 inch of mulch is now only 2 inch, since the lower 2 inch had turned to soil. Even though it look like the same height as before.
What method of mulch management is better? Do I need to dig deeper and remove soil every so many years?
Residence: S. California. Zone 9.