The Garden Fanatic
"October is the fallen leaf ...."
-- Hal Borland
"Old gardeners never die ... they just fade away."
-- Anonymous
There have been a number of defining moments in my life: the first
kiss, leaving Laguna for college and marrying Catharine come to mind
quickly. I also recall selecting my first tree for a client, and it
was Fritz Toohey who sold it to me.
I was thinking about Fritz last week, as I noted that the
liquidambars and sycamores had begun to turn color in and around
Laguna. It had been awhile since we had last chatted, so I promised
myself that I would call him soon. Later that day, my
ever-inquisitive wife asked, "Why do some trees turn color?" And I
answered ....
Trees are planted wherever one chooses, but grow naturally only
where they can survive and prosper. In the wild, environmental
factors determine success or failure for a particular species of
trees.
Northern latitudes and higher altitudes, as on our recent mountain
visit, are characterized by cold winters and periods of winter
drought (unavailability of water due to snow). Deciduous trees
(cottonwood, maple, etc.) must shed their leaves to protect against
adverse conditions, and are native to these climes.
The desert, which has an excess of summer heat, and Laguna Beach,
which does not provide sufficient winter cold, are inhospitable to
many species of deciduous trees. Although many cultivars of trees
provide fall color in Laguna, one must travel as far away as Maine,
or as close as Idyllwild, to view the truly spectacular turning of
leaves.
Every broadleaf, deciduous leaf is attached to its tree by a stem
called the petiole. The petiole not only holds the leaf, but contains
the conducting pipelines, which carry water (xylem) to the leaf and
returns food (phloem) out of the leaf to the plant. This versatile
structure also rotates the leaf to the proper angle to receive more
sunlight and elongates to ensure that each leaf reaches enough light.
As a leaf matures, it changes in color from light green to darker
green. When temperatures become chillier and water becomes less
available, a biological signal is sent to the tree that winter is
approaching. From late summer to early fall, a ring of cork grows
across the petiole of many deciduous trees, slowly blocking the
pipelines of water and food to and from the leaf. These cork cells
are called incision cells. By early October, the conducting
structures of the leaf are completely sealed off. Depending on the
