In the Santa Barbara area coast live oak trees (Quercus agrifolia) are dominate natives in our yards, our streets, our parks, and the undeveloped areas around us. The natural habitat of the coast live oak is on the coastal side of the mountains where fog is more common, there is less chance for winter frost and summers are cooler than inland. The structure of the coast live oak is wider than tall creating an umbrella or domed canopy shape with large branches curving back to the ground, sprouting roots and supporting the upper parts of the tree. The coast live oak needs well-drained soil so the roots aren’t soggy especially in the summer.
There are a variety of websites dedicated to description and care of the coast live oak.
The California Oaks Foundation has extensive information on all species of oaks within California (http://www.californiaoaks.org/).
The USDA/NRCS Plants Database has a great plant guide (http://plants.usda.gov/plantguide/pdf/cs_quag.pdf)
The US Forest Service includes a detailed overview of the species (http://www.fs.fed.us/database/feis/plants/tree/queagr/all.html)
Don’t forget to check out the collection of books about oaks that can be found at your local library or at the Santa Barbara Botanic Garden.
Coast Live Oak Tree Care
Here are some important facts on caring for you coast live oak, whether you planted it or the tree has been around for years. Care of the coast live oak can be tricky. We get many questions on how to care for these oak trees: Are they healthy? Do they need to be trimmed? Should the tree be removed? Should I be concerned about the branches over my house? How often should I water my oak tree? Each tree and tree location presents different answers to the above questions. Here are a few guidelines.
Coast live oak trees as mature trees grown in the native landscape might not be what we might want in our yards or streets. The domed canopy shape usually drapes the branches almost to the ground blocking the view and many times taking up more room than we want. Commonly coast live oaks are trimmed and pruned into the ‘traditional’ tree form of bare trunks and a full canopy overhead. Can a coast live oak stay healthy with this change in architecture? It can if done properly. Excessive pruning of leafy limbs can expose the inner branches to sun damage or cause the tree to put out epicormics (new sucker growth along a previously bare branch). Therefore pruning should be done in the winter months so that the sunlight is less direct, the temperature is lower (less water stress), and the tree is essentially dormant just waiting to spout out new leaves and branches.
When growing in the natural environment, coast live oak and other oaks are relatively tolerant to most diseases. Common diseases affecting landscape coast live oak in the Santa Barbara area include fungi causing crown and root rot.
Crown rots can cause twig/branch die-back and wilting, yellow or browning of leaves, and lesions on the bark accompanied by oozing of a dark liquid. The decline is usually slow, occurring over a period of years (5 – 10 years). However if identified early in decline the tree can usually be saved by removing the infected branches.
Root rot, commonly caused by the fungus Armallaria, is ubiquitous in the oak root system. However, when the water regime is changed by irrigating during the normally dry summer months or the roots are exposed or damaged during construction activities, the fungus can grow. Symptoms include branch die-back and yellowing or thinning of the leaves and in extreme cases the fungus can appear as a white, fan-like growth (shelf-mushroom) at the base of the tree or along the trunk. If the fungus is visible then the infection is usually extensive and, if the tree poses a risk to structures, the tree should be removed or pruned to reduce branch weight.
Insects inhabiting a coast live oak are common and not always detrimental to the health of a tree. For example, an oak gall is a harmless swelling of leaves or trigs caused by a wasp laying her eggs. Another insect commonly seen around the Santa Barbara area is called the oak moth and can the larval form can eat most of the leaves from a tree. Healthy trees will recover and regrow leaves in the spring. However if an oak tree is under water stress, infected with a fungus, or have root damage the oak tree might not recover. Wood-boring insects, like the Goldspotted Oak Borer, can cause widespread damage if not identified and contained. Check out the University of California, Riverside’s website (http://cisr.ucr.edu/goldspotted_oak_borer.html) for information on the Goldspotted Oak Borer.
As with the fungus, insects will not usually cause much damage if trees are healthy.
Water and Irrigation
Coast live oak trees are native to our Mediterranean climate of warm, wet winters and hot, dry summers. So these oaks normally do not need any additional water, especially in the summer months. Moist soil near the base of the tree during the warm summer months can promote crown and root rot. And especially do not allow irrigation sprinklers to spray directly on the tree (bark or leaves) as this can promote crown rot.
This past summer, with little winter rain and long hot months, has been slightly different. Irrigation was probably necessary for most oaks but only outside the edge of the canopy, and no more than twice a month to ensure the ground did not remain overly moist for a long period.
Coast live oak as landscape trees have unique structural challenges. Oak trees have character. They can be scraggly, gnarled, asymmetrical, with branches going every which way. They can have cracks, broken branches, burn scars from wildfires, and cavities. Each issue by itself is not a risk, but combine and add fungus or insect damage and parts of the oak tree could fail. The good news is that oak trees rarely fall all at once from the base. The bad news is medium to large branches can fail at any time (remember the blog on Sudden Limb Drop?) and the cause is not always obvious. A large cavity at the base can be perfectly normal as a trunk only needs about 25% to support the tree or the cavity can be from fungus, insect or even animal damage. With oaks, and all trees for that matter, it is nearly impossible to look inside a tree (there are methods of using computer imaging and special tools but being able to interpret the results is not always 100% accurate) so trying to determine when a tree or parts of a tree are going to fail is challenging. Think about medical doctors before x-rays, CAT scans, or MRI imagery.
Oak Tree Risk
Still confused about how to take care of your tree? Mature coast live oaks can look gnarly with broken branches, cracks, and crevices all of which can be perfectly normal. Or not. That is where a certified arborist knowledgeable in our local oak trees becomes important.
Branch Out Tree Care
That is where we can help. Our arborists are highly knowledgeable about oak trees both in their natural environment and as landscape trees. We have extensive experience in tree care (trimming, pruning, cabling, structural repair), identification of diseases or pests, and risk and structural assessment. Give us a call to have us look at your trees and develop a long-term maintenance plan.