Landscaping Around Oak Woodlands
Oak woodlands are among the most valued and prevalent component of the California landscape. Over 20 species encompass approximately 1/6th of the state’s total landmass. Aside from their aesthetic appeal, oaks increase environmental value by providing habitat for wildlife, shading, erosion control, wind protection, pollution reduction, and noise screening. Native oaks are perfectly adapted to thrive in California’s unique Mediterranean climate, but with increasing development over the past few years, there has been a dramatic decrease in the prosperity of oak woodlands.
Among the biggest problem is the misconceived notion that oaks are hardy and can withstand any degree of disturbance. While young oaks are tolerant of their environment, as they mature, they do not adapt well to changes. Construction that alters drainage, trenching, paving, and irrigation can weaken or kill healthy specimens. Whenever building on a site with established oak woodlands, precautions should be taken to ensure their preservation.
An oak’s root system is most susceptible to problems with construction. A tree has two types of roots: sinker roots grow vertically and penetrate deep within the soil. Lateral roots, however, are shallow (usually within the top 3 feet of soil) and can spread as much as 90 feet horizontally outward from the trunk. Knowing the size of this root zone is important because mechanical and chemical injuries often occur as a result of development on this area. To avoid root damage, one should follow these guidelines:
Do not let water accumulate: Saturated soil leads to crown and root rot fungi. Take precautions, such as installing French drains, to carry water away from root zone.
Do not compact soil: Often during construction, equipment and traffic lead to the compaction of soil which causes root injury. Eliminate or alleviate pressure by covering the root zone with mulch, not adding fill, and not installing paving near the trunk.
Incorporate appropriate plants species: Because oaks do not tolerate irrigation well, it is important to add other plants that do not require irrigation (especially in the dry summer months). Appropriate choices include:
Latin Name Common Name Growth Habbit
Adenostoma fasciculatum Chamise Shrub
Arctostaphylos manzanita Manzanita Shrub
Dendromecon rigida Bush poppy Shrub
Eriogonum arborescens Santa Cruz buckwheat Shrub
Fallugia paradoxa Apache plum Shrub
Rhus ovata Sugarbush Shrub
Aesculus californica California buckeye Small tree
Prunus lyonii Santa Catalina cherry Small tree
Baccharis pilularis Dwarf coyote bush Ground cover
Salvia sonmensis Creeping sage Ground cover
Zauschneria californica California fuchsia Ground cover
Dudleya sp. Live-forever Perennial
Salvia ‘Dare’s Choice’ Hybrid sage Perennial
Agave deserti Desert century plant Accent plant
Stipa puchra Purple needle grass Grass
Eschscholzia californica California poppy Annual
Ceanothus ‘Ray Hartman’ Hybrid ceanothus Shrub
Cercis occidentalis Redbuds Shrub
Mahonia pinnata California holly grape Shrub
Vitis californica California wild grape Vine
Ceanotus maritimus Maritime ceanothus Ground cover
Dinlacus aurantiacus Sticky monkeyflowers Perennil
Ribes viburnifolium Evergreen current Ground cover
Other appropriate plant selections can be found by contacting the California Oak Foundation.
Install utilities by hand: Usually done by trenching, this can cause physical damage to roots. Any necessary trenches should be dug by hand to avoid penetrating roots and bored at least 3 feet below the ground.
Maintaining oak woodland is usually best done with minimal interference. Oaks are relatively tolerant of natural California growing conditions. Some things to be watchful of are:
Mistletoe: A parasitic plant that weakens branches and leads to breakage. Controlling mistletoe depends on degree of infestation. Minor problems require cutting back bark while major infestation may require consulting an arborist.
Insects: Most insects do not do devastating damage to oak trees. Wasps’ eggs, for example, cause galls, which are harmless growths on branches. More serious insect infestations include pit scales and oak moth which cause leaf loss, change in leaf color, sticky branches, and twig die-back. If any of these symptoms occur, an arborist should be contacted.
The most important thing to remember when dealing with native oaks is that they evolved and thrived in the California climate without manipulation of any kind. The biggest mistake made when adding additional landscaping around them is the addition of nonnative environmental elements, such as irrigation, fertilization, and pruning. These practices need only be done when human action has caused alterations that diminish the health of the tree (such as breaking limbs or depleting soil nutrients).
