Amending San Diego's Poor Soil: An Ongoing Process

A Ramona residence with native topsoil created from Coastal Oaks.

      When clients ask me whether they need to improve their soil, I let them know the San Diego area has two types of dirt: poor and worse.  It’s an attempt at humor of course, but native soils here are high in mineral content and lack organic matter, due to the lack of lush plant communities that can annually drop inches of twigs and leaves that decompose into fertile soil.  And if the lack of organic matter is not enough, developers then grade properties to remove the scanty top layer of earth and expose bedrock and clay as the new soil surface. New home sites typically do not have any topsoil at all!  The top layer of soil where most plant growth occurs must be recreated before planting begins.

Healthy soil breaks down into of three components:

• Rock and mineral elements.
•  Decomposed or decomposing organic matter.
• Living organisms that break down organic matter into soluble nutrients.

     An ideal garden soil profile has half its actual volume dedicated to air and water, with the other half is comprised of the three bullet points – the soil components listed.  Healthy soil also must register a certain ph factor that is neither too alkaline nor acidic to allow plants to properly grow. 
     Healthy soil has been described as a living and breathing entity that has billions of microscopic organisms and a thriving population of earthworms churning organic matter into nutrient-rich matter.   A depleted, compacted site may take years of continual work before the soil can be considered sustainable, which means organisms are reproducing abundantly and organic matter has reached optimal levels.  It is a mistake to think that newly planted landscape plantings can grow and prosper into perpetuity once the initial soil amending is complete.  Even the best forest compost mixes have been used long before the garden enters its second decade.
     An ongoing program of replenishing the soil with composted mulches and organic fertilizers is needed for continued optimal plant growth and health.  It will an ongoing effort of periodic mulching and possibly nutrient replenishment to create a sustainable environment below the soil line, but plants can then grow and prosper into old age.  The evidence will be easily seen in healthy and happy maturing plants!

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