Question: I heard it is best to move rock away from my shrubs and replace it with mulch. What is your recommendation?
Rock can also be a mulch, and we call it that in our desert landscapes:rock mulch. We have three categories of mulches: organic, inorganic and living. Wood mulches are in the organic category. Rock mulches are in the inorganic category. Organic mulches, like wood mulch, give extra benefits to plants that rock mulches cannot.
Our desert creates its own rock mulch, and that's why plants that originate from desert environments can tolerate rock mulches. It is not that they grow better in rock mulch but rather that they survive better in it. Nearly all plants grow better with organic mulch rather than rock mulch when grown in our desert soils. Plants like most of our fruit trees, roses, iris, lilies and those which are not true desert plants perform better with wood mulch.Those that come from desert climates such as mesquites, acacias, desert bird of paradise, agaves, cacti, etc. will tolerate rock mulch better than nondesert plants. But in most cases, they still perform better surrounded by wood mulch.
Newly planted trees and shrubs should have wood mulch kept away from them a distance of about one foot the first few years of their life. After that they usually tolerate wood mulch in contact with their trunk. This is because the wood mulch keeps the soil too moist and can cause the trunk to rot.
Bob Morris is a professor emeritus in horticulture with the University of Nevada and can be reached at email@example.com. Visit his blog at xtremehorticulture.blogspot.com.