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John Thompson gave us an excellent lecture and
demonstration on oaks. Some pointers were:
- Observe oaks standing alone in nature. The trunks
grow upward for a ways, then branch out. The branches
grow up, down, and all around. The mature trees are wider
than tall, umbrella-shaped, with a number of apexes, and
open enough that the internal structure can be seen.
These are the characteristics that oak bonsai should
have.
- Oaks in California are being killed by a fungus in
the Phytophthora genus that also attacks Port
Orford Cedar and rhododendrons. A drench spray of Subdue
will control the fungus. Subdue can be purchased from
McCalif's but is extremely expensive.
- Oaks may be bought from nurseries or dug in the
field. Trees that have been repeatedly nibbled by cattle
or deer are especially promising material. (Be sure to
get permission from the owners of property where you wish
to dig.)
- Look for movement in the trunk. Don't worry about
leaf size. Bonsai techniques will reduce leaf size in
time. Defoliation in January every year works well with
Coast Live Oak. Cork Oaks should be defoliated less
often.
- When digging Coast Oaks, one often finds that the
main roots grow from an unattractive onion-shaped base
below the soil surface. If the tree is otherwise
desirable, it can be dug and grown for a few years in a
pot. One can then air-layer it.
- Another way to get a nice base with surface roots all
around is to saw off the entire tree, making, in effect,
a large cutting. The base is under-cut all around (up to
_ inch for a large tree). The exposed cambium is dusted
with rooting hormone. The tree is placed on a brick on
soil in a container and secured. The base is covered with
a few inches of coarse soil. (Akadama is a good choice.)
A callus will form from which surface roots will grow in
3-4 years. John advised us to rotate the pot frequently
to assure that roots will grow all around the base. A
heating mat under the container is a good idea too.
For his demonstration John used a Cork Oak. He had cut
the straight top off the tree two years ago to produce more
movement in the structure. He advised us when cutting a
branch to cut a little outside the collar at its base,
because preserving the collar promotes good healing.
John removed the surface soil to expose the surface
roots, then removed the tree from its deep container and cut
the root ball in half horizontally. He transferred the tree
to a shallow, 16" wide, plastic, aquatic plant container
available from McCalif's. He then teased a few roots out of
the root ball to make contact with the new, coarse soil. He
sprinkled some mycorrhiza (white fungus) on the roots and
added soil to fill the container and cover the surface roots
1-2 inches deep. Next year John will check the health of the
surface roots and if they are OK will cut more off the base
of the root ball. He expects that in 3-4 years he will have
a tree with well-distributed surface roots. John recommends
watering only when the soil is dry down one inch. He uses a
complete fertilizer such as Osmocote.
Kusamura thanks you, John, for a very informative talk
and demonstration.
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