Know your soil

The soil in our gardens is a mixture of
mineral particles derived from rock
weathering over millennia, air, water,
decomposed organic matter and living
organisms. Though all soils are based on the
same basic ingredients, they vary widely
because of differences in the way the
ingredients are combined.

Gardening Without Irrigation VII (Increasing Soil Fertility Saves Water)

Increasing Soil Fertility Saves Water

Does crop growth equal water use? Most people would say this statement seems likely to be true.

Actually, faster−growing crops use much less soil moisture than slower−growing ones. As early as 1882 it was determined that less water is required to produce a pound of plant material when soil is fertilized than when it is not fertilized. One experiment required 1,100 pounds of water to grow 1 pound of dry matter on infertile soil, but only 575 pounds of water to produce a pound of dry matter on rich land. Perhaps the single most important thing a water−wise gardener can do is to increase the fertility of the soil, especially the subsoil.

Gardening Without Irrigation VI (Fertilizing, Fertigating and Foliar Spraying)

Fertilizing, Fertigating and Foliar Spraying

In our heavily leached region almost no soil is naturally rich, while fertilizers, manures, and potent compostsmainly improve the topsoil. But the water−wise gardener must get nutrition down deep, where the soil stays damp through the summer.

Gardening Without Irrigation V (Windbreaks)

 Windbreaks

Plants transpire more moisture when the sun shines, when temperatures are high, and when the wind blows; it is just like drying laundry. Windbreaks also help the garden grow in winter by increasing temperature. Many other garden books discuss windbreaks, and I conclude that I have a better use for the small amount of words my publisher allows me than to repeat this data; Binda Colebrook's [i]Winter Gardening in the Maritime Northwest[i] (Sasquatch Books, 1989) is especially good on this topic.

Gardening Without Irrigation IV (Mulching)

Mulching

Gardening under a permanent thick mulch of crude organic matter is recommended by Ruth Stout (see the listing for her book in More Reading) and her disciples as a surefire way to drought−proof gardens while eliminating virtually any need for tillage, weeding, and fertilizing. I have attempted the method in both Southern California and western Oregon with disastrous results in both locations. What follows in this section is addressed to gardeners who have already read glowing reports about mulching.

Gardening Without Irrigation III(Keeping the Subsoil Open with Green Manuring)

Keeping the Subsoil Open with Green Manuring

When roots decay, fresh organic matter and large, long−lasting passageways can be left deep in the soil, allowing easier air movement and facilitating entry of other roots. But no cover crop that I am aware of will effectively penetrate firm plowpan or other resistant physical obstacles. Such a barrier forces all plants to root
almost exclusively in the topsoil. However, once the subsoil has been mechanically fractured the first time, and if recompaction is avoided by shunning heavy tractors and other machinery, green manure crops can maintain the openness of the subsoil.

Gardening Without Irrigation I I(Using Humus to Increase Soil Moisture)

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 available moisture than clay.
There are also new synthetic, long−lasting soil amendments that hold and release even more moisture than humus. Garden books frequently recommend tilling in extraordinarily large amounts of organic matter to increase a soil's water−holding capacity in the top few inches.

Gardening Without Irrigation I (Spotting a Likely Site)

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 bothdeep, 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!