Todd wrote:

My soil is "decomposed sandstone". Like Decomposed granite (also
called DG), only way uglier. Even the weeds have a hard time growing
in it. I would probably have better luck trying to grow things
with soil from the moon.

It would help to know your location, but it sounds more like your soil
drains too quickly, like trying to grow crops in beach sand... adding
fertilizer won't help if it just washes away. You need to amend your
soil with organic matter and some sort of inorganic water retension
material. It would definitely help to have several inches of good
quality topsoil added. Most plant nurseries carry a variety of
amendments and can advise for your area:
http://www.ext.colostate.edu/pubs/garden/07235.html
http://www.technogreencorp.com/water...t_aquafeed.htm
http://www.geltechsolutions.com/soil...ural-uses.aspx