By Carmen Kappos 
Inyo-Mono Master Gardener Volunteer 

While the words soil and dirt are often used interchangeably there are differences between them. Recently, Dustin Blakey, our local UCCE Farm Advisor, gave a talk called “Preparing Garden Soil on the East Side.” During this discussion Dustin outlined the job description of soil as performing the following tasks.  

In list form, soil : 

• Supports Plants
• Is a Reservoir for Water and Nutrients
• Makes Gas Exchange Possible
• Supports Biological Activity 

Notably, soil is a complex ecosystem that supports plant life and growth, while dirt is a bunch of material that can’t support plant growth. Dirt may contain some of the same materials as soil and at the same time may not be enough volume to support plants, or it could be too loose to support plants, or be void of biologic activity. 

In our own gardens, a good way to enhance the job performance of our soil is by adding well composted organic material.  Organic material enhances the structure of soil by improving soil aggregation. The organic matter acts as a glue to bind soil particles into larger clumps called aggregates.   It also improves the soil structure by creating pore space between aggregates, and providing surface capacity to hold water and nutrients.  In that way, soil can better avoid water run off by improving water infiltration to the soil. Additionally, organic matter has a negatively charged surface that attracts and retains water, allowing soil to hold more water. 

Improving the soil structure by adding organic matter to our garden soil also helps increase aeration in the soil making needed oxygen more available to plant roots. Compaction of soil can also be reduced with the addition of organic matter. And importantly, the addition of organic matter promotes healthy soil biology by encouraging and feeding a variety of life in the soil from earthworms and millipedes to fungi and microbes. 

Whether adding well composted organic material in a new bed for plants or gently turning it into an existing bed; at the end of the day, dirt is the stuff that you brush off your clothes with the satisfaction of having helped your soil perform its job description.