Recently I tore up some grass to enlarge a flower bed. The soil under the removed grass is very hard. What is the best ingredients to add to the soil for best flower growth?

We recently bought a house in semi-rural Connecticut, beautiful but with some serious soil problems! The soil is such dense clay and filled with SO many rocks that it took me 5 hours just to dig holes for 8 smallish rhodedhendron. The thought of trying to dig up enough for foundation plantings or digging the trench for a much-needed front walk has me nearly in tears. I'm used to nice, already-worked soil that just needs a little turning! Any help or pointers on where to start would be *greatly* appreciated. It's clear that my little spade isn't going to do the job, but I really don't have a clue what will. The books and sites I've found all seem to start with instructions like "Dig a trench 10in deep" with no ideas about how to do that in adverse soil conditions. Thanks in advance! -Thistle