Q: I am looking at trees to plant in my yard. Are there any specific ones that I should avoid?
Here are some truly awful trees that I recommend against planting. Most of these are on the invasive species list. Unfortunately, this does not mean that you won’t be able to find them for sale in local garden centers or nurseries.
Tree of Heaven (Ailanthus altissima) – This tree can reach over 80 feet and grows quickly in poor, dry soils. It has smooth bark and very large, tropical-looking leaves that smell like burnt rubber. It spreads through both seeds and root suckers and can quickly take over your property. Worst of all, it is the primary host tree for the spotted lantern fly (another invasive pest species). Its roots will spread aggressively and uproot driveways, sidewalks, and foundations. It is allopathic, meaning that it releases chemicals into the nearby soil that prevent anything else from growing. This tree may simply show up on your property and, if it does, you’ll want to remove it immediately.
Tamarisk (Tamarix parviflora or Tamarix ramosissima) – Also known as Salt Cedar. These trees can be found along railroad tracks, river banks, and salt marshes. They have fine, narrow, almost delicate-looking leaves and bear pretty pink flowers. Don’t let their dainty appearance fool you! They form dense thickets which tend to crowd out any nearby native plants. Their leaves excrete salt, which is a rather unfriendly thing to do to any neighboring plants.
Eucalyptus (blue gum or red gum) – Eucalyptus trees are native to Australia and are very well-suited to Southern California’s hot, dry climate. They are fast-growing and useful as shade trees, bird habitat, and even honey production. Unfortunately, they are highly flammable due to their high oil content. The wood is brittle, so branches tend to break off (this can be a real problem, especially when the tree is several hundred feet tall). Their root system is aggressive and can interfere with irrigation systems and water pipes. Finally, they will reseed and spread, forming dense groves that crowd out native species.
Ornamental Pear (Pyrus calleryana) – No list of loathsome trees is complete without mentioning the Callery pear. For some reason, this tree continues to be a favorite of landscapers for public areas. It grows quickly to a height of 50 feet and bears large quantities of white flowers that smell like rotting fish. In addition to the foul stench, they are highly invasive as they spread through thorny root suckers. They also spread fire blight, which kills useful trees like apple, (edible) pear, and quince. It is a truly detestable tree.
Los Angeles County
mglosangeleshelpline@ucdavis.edu; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/
Orange County
ucceocmghotline@ucanr.edu; http://mgorange.ucanr.edu/
Riverside County
anrmgriverside@ucanr.edu; 951-955-0170; https://ucanr.edu/sites/RiversideMG/
San Bernardino County
mgsanbern@ucanr.edu; 909-387-2182; http://mgsb.ucanr.edu