in inches)*

Location Duration Amount

Umatilla/Yakama Valley April-October 30
Willamette Valley May-September 16
Puget Sound May-September 14
Upper Rogue/Upper Umpqua Valley March-September 18
Lower Rogue/Lower Coquille Valley May-September 11
NW California April-October 17

*Source: _The Water Encyclopedia_

In our region, gardens lose far more water than they get from
rainfall during the summer growing season. At first glance, it seems
impossible to garden without irrigation west of the Cascades. But
there is water already present in the soil when the gardening season
begins. By creatively using and conserving this moisture, some
maritime Northwest gardeners can go through an entire summer without
irrigating very much, and with some crops, irrigating not at all.

Chapter 2

Water-Wise Gardening Science

Plants Are Water

Like all other carbon-based life forms on earth, plants conduct
their chemical processes in a water solution. Every substance that
plants transport is dissolved in water. When insoluble starches and
oils are required for plant energy, enzymes change them back into
water-soluble sugars for movement to other locations. Even cellulose
and lignin, insoluble structural materials that plants cannot
convert back into soluble materials, are made from molecules that
once were in solution.

Water is so essential that when a plant can no longer absorb as much
water as it is losing, it wilts in self-defense. The drooping leaves
transpire (evaporate) less moisture because the sun glances off
them. Some weeds can wilt temporarily and resume vigorous growth as
soon as their water balance is restored. But most vegetable species
aren't as tough-moisture stressed vegetables may survive, but once
stressed, the quality of their yield usually drops markedly.

Yet in deep, open soil west of the Cascades, most vegetable species
may be grown quite successfully with very little or no supplementary
irrigation and without mulching, because they're capable of being
supplied entirely by water already stored in the soil.

Soil's Water-Holding Capacity

Soil is capable of holding on to quite a bit of water, mostly by
adhesion. For example, I'm sure that at one time or another you have
picked up a wet stone from a river or by the sea. A thin film