Building a Southern California Garden
(soil, water, and climate)
Soil, water and climate are the three most fundamental considerations when building a successful garden. Unfortunately the wonderfully adaptive diversity of life that enables living things to grow anywhere in the world, also means that there is no single universal combination of soil, water, and climate conditions that fulfills the environmental requirements of all plants. While you will find scores of books discussing these issues, few point out the unique conditions in Southern California and many fail to provide useful advice. Southern California is dryer and more temperate than most of the rest of the United States. This results in a gardening experience rarely matched anywhere else. Let's consider some of these issues...
Due to the low rainfall, our soil is often more alkaline and lower in organic material than that in eastern gardens. In general, do not add lime or wood ash to your soil to make it more alkaline (a common technique back east where the soil is often too acidic). The single most productive thing you can do for your soil is to add as much organic matter (compost, leaves, grass trimmings, etc.) as you can.
more about soil... (coming soon)
In our climate, your garden must be irrigated (and mulched to keep evaporative losses down). Although your irrigation needs can be lightened with good design (see Xeriscape Gardening -- coming soon), most vegetables and many other popular plants require more water than Mother Nature provides locally. Unfortunately, our water tends to be too salty and alkaline. Alkalinity can be countered and "buffered" to some extent by adding organic matter which is usually slightly acidic) to your soil and excessive salt accumulation can often be driven below the root zone with an occasional heavy soaking.
more about water... (coming soon)
While the cold Pacific Ocean currents, prevailing offshore (westerly) winds, and temperate latitude all conspire to give us low humidity levels and light rainfall, they also give us mostly cloud-free warm sunny days and moderate temperature fluctuations which results in an extended gardening season matched by few other areas in the US.
This is not to say that all of Southern California is characterized by exactly the same type of climate. Coastal, mountain, and desert areas experience significantly different climates mostly due their relative distances from the moderating ocean influence. Valleys, canyons, mesas, and mountainous areas also experience climatic differences due to differential heating & cooling of air masses and channeling & constriction of airflow generated by the land surface topology.
On the smaller scale, significant local climatic variations can occur for several reasons. These local variations are often called microclimates. Depending on the layout and topology of your garden, you might actually have several distinct microclimates to contend with.
In general, be wary of seasonal gardening advice not adjusted for the Southern California climate. Find out the specific climate "zone" that characterizes your area and try to determine the microclimatic variations within your garden.