Question: I have an 18-year-old velvet ash in a small (20 feet by 20 feet), rock-covered front yard. Does this tree do better with rock or wood chips around its trunk?
Plants that originate from non-desert or non-arid climates perform best growing in wood mulches in the landscape. They also do better growing in soils that have been amended at the time of planting. Plants such as velvet ash (aka Arizona ash), which is native to the desert and arid Southwest, tolerate desert soils and can be grown more successfully under rock mulch than non-desert plants. This also is true of many cacti and succulents. You will see them perform better if we amend the soil at the time of planting with some organic matter. In the case of your velvet ash, it can tolerate a rock mulch better than Japanese privet (native to Japan), which is frequently placed in rock landscapes here with very little success.
Bob Morris is a professor emeritus in horticulture with the University of Nevada and can be reached at firstname.lastname@example.org. Visit his blog at xtremehorticulture.blogspot.com.