Q. I often enjoy your pieces in the NLV neighborhood View, and your suggestion of replacing rock mulch with wood chips caught my attention. I have an 18 year-old velvet ash in a small (20' x 20'), red rock covered front yard. Does this tree do better with rock or wood chips around its trunk?
A. This is where my comments can sometimes be misconstrued. What I am trying to tell people is that for the most part, plants that originate from nondesert or nonarid climates perform best growing in wood mulches in the landscape. They also do better with growing in soils that have been amended at the time of planting with organic materials like compost.
Plants like Velvet ash (aka Arizona Ash) which is native to the desert and arid Southwest, TOLERATES desert soils and so can be grown more successfully under rock mulch than non-desert plants. Nearly all plants perform better with a higher organic content in the soil but desert plants, like Velvet ash, can TOLERATE rock mulch landscapes.
This is true of many cacti and succulents as well. You will see them perform better if we amend the soil at the time of planting with some organic matter like compost.
In the case of your Velvet ash, because it is native to the arid and desert Southwest, it can tolerate rock mulches better than say Japanese privet (native to Japan) which does not tolerate rock mulch very well at all but is frequently placed in rock landscapes here with, over time, very little success.