atively inaccessible.

Soil compaction reduces the overall supply and exchange of soil air.
Compacted soil also acts as a mechanical barrier to root system
expansion. When gardening with unlimited irrigation or where rain
falls frequently, it is quite possible to have satisfactory growth
when only the surface 6 or 7 inches of soil facilitates root
development. When gardening with limited water, China's the limit,
because if soil conditions permit, many vegetable species are
capable of reaching 4, 5, and 8 eight feet down to find moisture and
nutrition.

Evaluating Potential Rooting Ability

One of the most instructive things a water-wise gardener can do is
to rent or borrow a hand-operated fence post auger and bore a
3-foot-deep hole. It can be even more educational to buy a short
section of ordinary water pipe to extend the auger's reach another 2
or 3 feet down. In soil free of stones, using an auger is more
instructive than using a conventional posthole digger or shoveling
out a small pit, because where soil is loose, the hole deepens
rapidly. Where any layer is even slightly compacted, one turns and
turns the bit without much effect. Augers also lift the materials
more or less as they are stratified. If your soil is somewhat stony
(like much upland soil north of Centralia left by the Vashon
Glacier), the more usual fence-post digger or common shovel works
better.

If you find more than 4 feet of soil, the site holds a dry-gardening
potential that increases with the additional depth. Some soils along
the floodplains of rivers or in broad valleys like the Willamette or
Skagit can be over 20 feet deep, and hold far more water than the
deepest roots could draw or capillary flow could raise during an
entire growing season. Gently sloping land can often carry 5 to 7
feet of open, usable soil. However, soils on steep hillsides become
increasingly thin and fragile with increasing slope.

Whether an urban, suburban, or rural gardener, you should make no
assumptions about the depth and openness of the soil at your
disposal. Dig a test hole. If you find less than 2 unfortunate feet
of open earth before hitting an impermeable obstacle such as rock or
gravel, not much water storage can occur and the only use this book
will hold for you is to guide your move to a more likely gardening
location or encourage the house hunter to seek further. Of course,
you can still garden quite successfully on thin soil in the
convention