Oaks in our landscapes require a dry environment under them. Finding drought tolerant shade plants that will
thrive can be difficult. Many of the plants that are found in garden centers shade sections lust for water.
Appropriate planting under oak trees is critical if we are to maintain our natural oak forest.
Increasingly water agencies are restricting the use of water or are raising the cost dramatically. And
community planners are requiring ecologically sensitive plant lists for site plans for construction projects.
For the sake of the wallet as well as maintaining the continuity of the plants in the landscape there is a
lot of motivation for using drought tolerant plants under your oaks.
This dry shade garden list includes both natives and introduced landscape plants that will thrive on the
conditions that are ideal for planting under our native Coast Live Oaks,
Quercus agrifolia. The coolest and most comfortable part of the garden during the heat of the
day is under the trees. It is only natural to want to make this area attractive. These areas are often
planted with lawns, azaleas, fuchsias and many other water loving plants. In the long run this is no good
for the oak trees. The oaks may not show stress immediately but over 10-20 years it can spell disaster. In
the interim the oaks keep looking worse and worse. And the risk of the tree falling on people increases
dramatically.
The extra irrigation coupled with the fertilizing in the area of the trees with concentrated ammonia based
fertilizers destroys the native soil fungi. This creates conditions ideal for the oak root fungus to get a
foothold. The bad fungi don't attach to good fungi like they do to naked roots.
While oak trees can grow in wet conditions (I have seen old trees growing in creek bottoms with water
running over the roots all year) they can not tolerate a change of diet without a rapid decline or death.
The problem zone extends to the drip line of the tree and somewhat beyond. This means the entire area
shaded by the tree and probably half again that radius of the tree has roots from that tree. Any change
of grade or increase in the irrigation within this zone compromises the trees.
Two great books on this theme are listed below.
