>> I've been mowing as close as possible and layering with cardboard before adding planter's mix to make raised beds. Figured the worms would eventually
I see you already know ho to save hours of work and gallons of sweat. Let time and nature do the hard work!
I picture the OM, water and NPK leaching out of the top layers and enriching the underlying clay enough to attract worms and roots.
By the way, do you have drainage problems with the clay? If the RBs are 100%
above grade, I guess not. But once the below-grade clay is softened and opened up, that deep root zone might fill with water after a rain and hold it long enough to drown roots.
I make sure that the hard clay floor of my RBs slopes towards one edge or corner, and add a slit trench to drain it to a yet-lower spot. But I usually excavate beneath each RB when I create it, and amend the sub-clay a little, so that part of the new bed is sunken below grade, and the rest raised above grade.
My RBs tend to dry out pretty fast, especially at the corners. Sometimes I line the walls or corners with heavy plastic cut from bags of bark mulch, to hold more water in.
