Planting under a mature tree should be
avoided or done very carefully so that you do
not lead to the demise of the tree. Plants will
compete for the much needed moisture of the
tree and watering the new plants to assure
their survival will cause the tree to put up more
surface roots.
Planting should be at least a foot away from all
trees and for oaks it is recommended that 6 to
10 feet be allowed away from the trunk.
Insects may be introduced to the tree through
the planting and soil amendments.
If you are committed to planting under the tree
use small plants that require a tiny planting
hole and that are drought tolerant. If you
encounter a root, move over a bit, and do not
cut the roots of the tree.
Don't alter the grade of the soil or change the
soil's pH very much. Even adding a layer of
soil that is more than 2 inches deep can
reduce the amount of moisture and oxygen
available to the tree and hinder gas exchange
to existing roots, causing trees to suffer or
even die.
As always, mulch is desired. Two inches of
mulch will conserve moisture and keep weeds
down. Mulch should be at least 12 inches away
from the base of the tree to avoid rot and
disease.
