Question: We have a 20-year-old olive tree in our front yard diagnosed with verticillium wilt disease. The north third of the tree appears to be healthy. If we remove this tree, what distance from the old hole is needed for the new tree? We would like a replacement tree to provide shade. We are looking at oak, pine, ash, spruce or fir.
That’s unfortunate. Hopefully, the diagnosis was correct, and it is not something else that caused it. The information you received about the disease sounds correct. This disease is present in the soil and enters the tree via the roots.
Olive has very few pest problems and is an excellent tree for the desert. Verticillium wilt disease is rare in olive here but does occur. Symptoms include the death and dieback of individual limbs for no apparent reason.
Trees resistant to verticillium wilt disease and are good choices for you in our desert include live oak, such as heritage or holly oak, ornamental pear, European pear, honeylocust, apple, crabapple and any of the conifers, such as pines.
Eucalyptus is also resistant, but a lot people do not like eucalyptus since it can be messy. I would not recommend spruce or firs because they do not grow well in our climate.
If you want warmth from the winter sun then conifers (pine) or any evergreen tree (such as our southern oaks) are not a good choice for you. I would stay with ornamental pear or honeylocust for seasonal shade, disease resistance and good looks.
If you stay with verticillium-resistant trees, planting in the same general area should not present a problem.
Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.