What is your maintenance routine for these 'mulched' beds??? Are you removing mulch and replacing it each year, or just adding an aesthetic layer each Spring???
Around here, we put down Preen before the mulch, then again after the mulch, in May... there is probably too much irrigation on your beds to get CG to grow in mulch... pre-m does wash away easily in mulch regardless of what the manufacturer claims... Roundup the young plants each month or more as necessary...
Now that I know that clay's texture(platelets) has nothing to do with water infiltration, percolation, or drainage,,, I wonder what does...