Ask Mr. Smarty Plants

I am amazed at a 50-year old mimosa, maybe it should have its own museum.They are typically fast growing and short-lived. Since at the Lady Bird Johnson Wildflower Center we are all about the use of plants native to North America as well as to the area in which they are grown, we have no information on the mimosa in our Native Plant Database. For more complete information on the tree, see this site Albizia julibrissin (USDA Forest Service), and notice especially the section on Care and Management. You will learn that the mimosa is a weak-wooded tree, with branches and even trunks often splitting in storms. They are also vulnerable to many pests and diseases, including Mimosa (vascular) wilt, which is fatal to the tree, and is becoming more widespread. The bark is thin and easily damaged from mechanical impact (like a weedeater).

You may realize we don't recommend planting this tree and, in your case, would recommend your trees be replaced with a native tree that does not have the problems the mimosa does. And, finally, in California you should be especially cautious about invasive trees, which the mimosa is. This Plant Conservation Alliance Least Wanted List tells you that because the mimosa tree can grow in a variety of soils, produce large seed crops, and resprout when damaged, it is a strong competitor to native trees and shrubs in open areas or forest edges. If you remove the trees, you might consider replacing them with Chilopsis linearis (desert willow) or Prosopis glandulosa (honey mesquite), both of which are native to California and have a similar lacy, almost fern-like, look. 

Chilopsis linearis

Chilopsis linearis

Prosopis glandulosa

Prosopis glandulosa