>> very firm on top, almost forming a hardened crust on the surface.
...
>> most noticeable in the predominately clay based bed, but also to a lesser extent in the more sandy loam based beds
In my beds (VERY heavy clay amended with not-enough compost), rain or mini-sprayer irrigation will "pound" the surface so that it reverts back to clay, hence becoming crusty when dry. I interpret that as a cry for help: "Mulch me!"
