By Greg Cloyd, with Bruce Baker
At a recent advanced study group
meeting, eastern white cedar, or arborvitae, (Thuja occidentalis)
pruning, foliage plane maintenance, and pinching practices were
Thuja occidentalis is a fragrant, evergreen, false cedar of
North America. It is differentiated from its western cousin (Thuja
orientalis) by its smaller size, prominent resin glands, slight
differences in cone morphology, and its un-winged seeds. It grows
as a telephone-pole-straight tree of moderate height in its
range. Farther north, in Canada, it is a twisted and contorted,
wind- and snow-tortured, deer-browsed, small tree of bog and
limestone lakeshore. Along the Niagara escarpment and in Quebec
it is a cliff-dwelling ancient dwarf growing less than an inch
in radius per century.
Arborvitae is very amenable to bonsai culture, readily tolerating
a wide range of soils, fertilizers, and climates. It is impervious
to poor water, soggy conditions, and shallow pots. It can be
twisted in a knot, air-layered, repotted out of season, and
manipulated with impunity. It has a pleasantly shaggy bark. The
species is widely available in the wild and in landscape
One physiological feature of the plant is worth noting. Each
hydraulic pathway, cambial lifeline, or xylem and phloem conduit
system, is sectored-completely divided from the rest of the plant.
From a practical viewpoint, this means that each major
root supplies one side of the tree or one major branch. If the
root or branch is killed, that entire portion of the plant will
die. This phenomenon is seen in other trees, but is strikingly
dramatic with white cedars. For this reason, collected white
cedars should be allowed to establish in a growing pot for at
least two growing seasons prior to styling. Otherwise, you risk
building a design around a branch that is condemned to wither
due to lack of a lifeline.
Illustration 1-(10x magnified frond tip) This shows
the scale structure with prominent resin glands of a
magnified cedar frond tip and where it is
The most pressing challenge of creating effective cedar bonsai
is foliage management. Cedar is possessed of a coarse,
foliage frond, which emerges alternately at varying angles above
and below the horizontal. This gives the foliage fans a somewhat
unkempt appearance. Because of this, many people find cedar
unattractive. The foliage is, additionally, very shade intolerant.
The shade intolerance of cedar is somewhat similar to Hinoki
cypress. Cedar demands attention to annual cleaning and thinning
chores, as well as frequent pinching to maintain "tight"
contours. Full sun exposure, good air circulation, and pot
along with moderate fertilization and proper pinching technique
must be observed. Beyond using the interesting collected trunk
forms to full advantage, artistic handling of the foliage is
the challenge of the plant. Some artists tightly pinch their
branches into solid pads, especially on larger collected trees.
The solid pad de-emphasizes the coarse frond, and the collected
trunk thus steals the show.
Illustration 2-(Whole cedar frond) The outer tips of
the frond are
pinched using the traditional technique. The arrows show the
interior leader, which will grow into the new leader of the bra
Another approach to foliage management
I've observed is to use much more open and airier foliage planes,
leaving each frond fully visible. This technique has been
well used by Paul Chong of Toronto. Paul does not wire branchlets
into flat planes. Instead, he emphasizes the unique fronds of
cedar, rather than obscuring them in a densely pinched pad or
overpowering their character by flattening the planes with wire.
In leaving fewer fronds, the individual character of the plant
and the complex nature of the frond seem to be more beautifully
revealed and the individuality of the species preserved. I get
the sense that I'm looking at an ancient cedar rather than a
generic bonsai when I view Paul's plants.
A final note about white cedar foliage is that once a frond is
fully differentiated, one side faces the sun and the other side
is shaded, just like the leaves of a deciduous tree. If, as a
result of bonsai training, the shady side is exposed to the sun
and the sunny side is shaded, that frond is almost certain to
Bruce Baker and I have observed the growth pattern of this plant
and commented on the compound nature of the frond. Bruce has
observed that the branch leader, or apical meristem, of the
is interior to the last fully exposed frond (see drawings). The
apical leader is round in profile as opposed to the flat profile
of a frond. The leader also has a more angular and less rounded
scale pattern. Simple pinching of the tips of differentiated
fronds misses this branch leader and does not fully promote
In our Great Lakes environment, early spring pinching of soft
frond tips seems to temporarily retard growth. This growth
is especially noticeable after repotting. This type of pinching
can even kill a marginal specimen. Greater success has been
in our hands, by waiting until the first spring flush of growth
is hardened. Removing or pinching the aforementioned "leaders"
after hardening off, as well as pinching the frond tips, promotes
a profusion of interior budding (back-budding). This causes the
emergence of multiple new interior "leaders" as well
as complex "staghorn" growth of the remaining fronds.
The new fronds and leaders may emerge anywhere frond scars are
visible (young, smooth, tan bark with abscission pits, rather
than shaggy old bark) as well as on new green wood. The buds
may also emerge at branch crotches. As with any bonsai, the new
leaders may be allowed to grow and lengthen the branch, or pinched
to maintain the current silhouette.
The rounded apical meristems of the new leaders can be removed
at any time during the growing season to promote interior budding
and to induce new growth of the existing frond tips. It is
beneficial to do this to very old collected specimens that have
grown in harsh environments and are already dwarfed by their
environments. These older specimens have become habituated to
growing very slowly and will continue to do so in a pot unless
steps are taken to induce more rapid growth. Removing the apical
meristems on ancient specimens can force them into a more rapid
growth phase that will also induce more vigorous root growth
and tend to ensure success of the plants as bonsai.
The remaining challenge of arborvitae is mid-summer thinning
to avoid shading out of interior branches. Any branch
shaded will quickly weaken. The shaded fronds will turn yellow
and drop in the fall. Caution is necessary when thinning the
plant after midsummer. Weak interior shoots may have already
been physiologically programmed to fade to yellow, abscise, and
drop. If you have removed the more vigorous shoots and left only
shoots programmed for fall shedding, you will be left with a
The branches to be "rounded up" for thinning should
be selected from "the usual suspects": up and down
branches, deformed or diseased branches, inward growing branches,
branches emerging from the inside of curves, overly strong or
weak branches, etc.
Even if you forget to pinch the foliage and dislike cedars, don't
despair. Your local deer population will appreciate your keeping
the plant in your collection and do the pruning work for you.
Whether your artistic aims are for more open and airy fronds
or for solid pads, modifying your pinching technique to include
the interior "leaders" after spring hardening of new
growth should produce more rapid ramification and shorter
times for your branches.
Bonsai: The Journal of the
Bonsai Society/Spring 2.000