Valley oak, also called California white oak, is native to California, and is most commonly found on deep valley soils with year-round soil moisture. Early settlers used the presence of valley oaks as an indicator of deep rich soil suitable for agriculture. At maturity, valley oak is the largest oak species in North America.
Culture for Valley Oak
Performs best on deep soils with medium to high organic matter and some source of summer water. Lower branches tend to become quite large and extended, while upper branches typically form an arching growth habit. In marginal site locations, supplemental fertilization and addition of organic matter is recommended.
Concerns about Valley Oak
Large branch failure due to over-extension and internal decay is common. Susceptible to oak pit scale. Commonly infested with a harmless but eye-catching gall caused by cynipid wasps. Not susceptible to sudden oak death, but may be infected by other Phytophthora species in poorly drained wet soil.
Management Practices for Valley Oak
Frequent pruning to reduce weight or subordinate extended branches will reduce failure potential. Excellent candidate for root invigoration due to need for rich organic soils. Pit scale treatments are effective but must be accurately timed to impact juvenile crawler stage.