I have yelled, cried, cussed, and thrown shovels at my soil and much to my irritation, none of it was effective. However, John and Bob's Penetrate Liquid Biotiller is. According to the plain white package, it's a liquid solution derived from saponin, a product of the yucca plant, and a molasses extract. It could be a combination of eye of newt and toe of frog, and after seeing how effective it is, I'd still buy it. I am convinced it was not born in a lab but is pure garden voodoo.
Here's how it works: a very plain package will arrive in your mail with two white bottles marked A and B. Pour some into your watering can and give it a stir. Take a pitchfork or long spike and poke holes into the worst, driest, hardest, most wretched soil in your garden. Saturate the soil with the Penetrate enriched water and Penetrate will pry your clay particles about like a crowbar. I'm serious!! I've been using it for two years and was amazed when it turned my Bed of Death and Misery into a beautiful part of the garden. It actually separates your clay soil allowing greater absorption of water and nutrients as well as increased air flow to your roots. It's only available in smallish sized packages but if I could buy in a 50 gallon vat, I would.
Here are a few early summer 2012 pictures of the Bed of Death and Misery after a fall and spring application of Penetrate.
To see some truly awful Before pictures, check out Redesigning the Bed of Death and Misery.
Penetrate can also be purchased at Amazon.com but I'd check out both sites to see where you can get the best deal.