KT wrote:

The soil here is hard-packed clay. I think I'd need dynamite to plant
anything. I know that if I add organic material it will help a lot,
but if I add inches of manure or compost, doesn't that change the
grade? We had problems with water in our crawl space in the last house
we had, and I don't want to raise the grade so that rain runs back into
the foundation. If I add the organic material, does it break down over
the summer so that the slope of my yard doesn't really change? I hope
this makes sense - I don't know if I am making myself clear. I want
better soil - but I don't want a wet crawl space.

My soil is adobe clay. To break it up, I scatter a generous amount
of gypsum over it, enough to coat the soil solid white but only
about 0.1 inch or less. Then, I lightly sprinkle with water to
start dissolving the gypsum into the soil without washing it away.
After that, I allow the garden sprinklers continue leaching the
gypsum into the soil. After about 2-3 weeks, I can dig without
having to scrape the sticky, pasty clay off the spade.

However you do it, once the soil is broken up and organic
amendments turned in, water will soak into the soil rather than
running off. Unless you get a downpour (or your soil freezes in
winter), you should not have to worry about water flowing towards
or under your house.

If you are still concerned, you might want to create low landscape
berms near enough to the house to be partially under your eaves.
Not only would these divert water, but they also are good for
plants that are sensitive to poor drainage.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening pages at URL:http://www.rossde.com/garden/