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
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 take a change of diet without extreme
risk of 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.
