posted 12 years ago
First question: do you have a lot of mesquite on your property? If you do, it is an indication that the rocky clay underneath is fractured enough to let roots penetrate through. There are some mesquite species that can send down roots 200' in search of water. If you clear out the mesquites, maybe your fruit trees can grow in succession after them and take advantage of whatever tillage the mesquite has done with its roots.
If, on the other hand, you have a bunch of grasses and short-rooted weeds, then things are going to be more problematic. You may have to start with what you have and build the soil in the upward direction. There are some plants that can force soils open. When I lived in Las Vegas, I had a hardpan of caliche about 3-7 feet below grade, but there was this one mulberry on the property that had managed to bust through and send roots to the water table below. Kind of amazing to see a mulberry tree thriving, with no irrigation, in a climate that only gets 4" of rain a year.
As for the annuals, you can grow a lot of vegetables on just 8" of topsoil. You're not going to get nice radishes and carrots, but you can get some nice lettuce, cabbage, kale, okra, squash, tomatoes, peppers, etc. If you single dig it to get rid of the golf balls and larger, you can have a nice annuals bed, especially if you amend on top in a lasagna garden fashion.