r example, on the gentler slopes of the geologic old
Cascades, those 50-million-year-old black basalts that form the
Cascades foothills and appear in other places throughout the
maritime Northwest, a deep, friable, red clay soil called (in
Oregon) Jori often forms. Jori clays can be 6 to 8 feet deep and are
sufficiently porous and well drained to have been used for highly
productive orchard crops. Water-wise gardeners can do wonders with
Joris and other similar soils, though clays never grow the best root
crops.

Spotting a Likely Site

Observing the condition of wild plants can reveal a good site to
garden without much irrigation. Where Himalaya or Evergreen
blackberries grow 2 feet tall and produce small, dull-tasting fruit,
there is not much available soil moisture. Where they grow 6 feet
tall and the berries are sweet and good sized, there is deep, open
soil. When the berry vines are 8 or more feet tall and the fruits
are especially huge, usually there is both deep, loose soil and a
higher than usual amount of fertility.

Other native vegetation can also reveal a lot about soil moisture
reserves. For years I wondered at the short leaders and sad
appearance of Douglas fir in the vicinity of Yelm, Washington. Were
they due to extreme soil infertility? Then I learned that conifer
trees respond more to summertime soil moisture than to fertility. I
obtained a soil survey of Thurston County and discovered that much
of that area was very sandy with gravelly subsoil. Eureka!

The Soil Conservation Service (SCS), a U.S. Government agency, has
probably put a soil auger into your very land or a plot close by.
Its tests have been correlated and mapped; the soils underlying the
maritime Northwest have been named and categorized by texture,
depth, and ability to provide available moisture. The maps are
precise and detailed enough to approximately locate a city or
suburban lot. In 1987, when I was in the market for a new homestead,
I first went to my county SCS office, mapped out locations where the
soil was suitable, and then went hunting. Most counties have their
own office.

Using Humus to Increase Soil Moisture

Maintaining topsoil humus content in the 4 to 5 percent range is
vital to plant health, vital to growing more nutritious food, and
essential to bringing the soil into that state of easy workability
and cooperation known as good tilth. Humus is a spongy substance
capable of holding several times more availa