The native live oaks of California’s coast and interior grow tall and broad, not just in the country’s oak forests, but in many urban parks and suburban yards. It is likely to eliminate these live oaks with kindness in a dry, warm Mediterranean climate, however. Take your advice from their natural habitat to determine how much water all these evergreen giants must drink.
Live Oaks and Water
Live oak trees are accustomed to sipping, not drinking, water — they’ve adapted to low to moderate rainfall in the warm, dry Mediterranean climate of California’s coastal ranges and valleys. These big, broad-crowned trees grow deep tap roots when young, but as they mature, their roots grow only under the soil’s surface, extending past the drip line of the crowns. Young trees may need irrigation once or twice monthly to become well recognized in dry years, but mature live oaks grow best in well-drained, moist soil. An excessive amount of moisture, whether from too much rain or well-intentioned irrigation, contributes to oak root rot. In addition, it can nourish Phytophthora ramorum, the fungus pathogen associated with Sudden Oak Death, which thrives in cool, foggy coastal weather. Nearby structure, compacted or clay soils and turfgrass lawns may also hurt the extensive root systems of live oaks.
Coast Live Oak
California, or shore, live oak (Quercus agrifolia var. agrifolia or Quercus agrifolia var. Oxyadenia) rises up to 100 feet tall in its native habitat, but in urban areas it rises 20 to 50 feet, frequently spreading as wide as it’s tall. Its brief trunk splits into several crooked divisions. Thick, glossy evergreen leaves keep water, which makes coastal live oaks moderate consumers of water, some of it provided by coastal fog. Provided your place receives 20 to 30 inches of annual precipitation, a coast live oak should not need extra water except in very long time. During droughts, moisten the top 8 to 10 inches of soil once a month with a drip hose.
Canyon Live Oak
Canyon live oak (Quercus chrysolepis) has gnarly limbs and compact size — the tree might grow as a tree no taller than 15 feet, a fantastic size for suburban lots and urban spaces. In its natural habitat as mountain ridges and in canyons along riparian borders, the tree might grow as tall as 60 feet. Its holly-like leaves are hairy when its own yellow acorns take two years to mature. Canyon live oaks need small water beyond that provided by winter rains and foggy days on the coast.
Interior Live Oak
Interior live oaks (Quercus wislizeni, Q. parvula, Q. shrevei) grow in shallow, dry soils and are low water-use trees, indigenous to interior regions with as little as 5 to 10 inches of precipitation per year. Such as the canyon live oak, interior live oaks grow in several varieties, some growing in 35 to 70 feet tall — and almost as wide — along with others growing just up to ten feet. Like other live oaks, they need well-drained soil for survival.