JM – Well…I don’t know about 4″, that almost sounds like it could qualify as thatching depending on the soil conditions. Definitely look for hardpan though. I’d say if you’re happy with the results keep with it.
Our spader will go through thick, tall cover crop like butter in ground that has been spaded before. In “virgin” ground it might take a couple passes and adjusting the depth of the spades on the second pass.
Our spader has a max depth of 10″. I can dig my hand down to that depth fairly easily on spaded ground. Even deeper on ground that’s been spaded a couple times now. On un-spaded ground, I’d be lucky to dig my finger in a couple inches. Not really due to hardpan but just soil compaction, which is another by-product of rototillers, discs and plows.