Japanese Gray-Bark Elm - Zelkova
General information: Zelkova is often listed as a replacement for
American Elm since it has roughly the same vase shape and grows 90 to 100
feet tall with a 60 to 80 foot spread. Zelkova is massive, with the trunk
capable of growing to four feet or more in diameter. It has a moderate
growth rate and likes a sunny exposure. Branches are more numerous and
smaller in diameter than American Elm. Leaves are 1.5 to 4 inches long,
turning a brilliant yellow, orange, or burnt umber in the fall.
This elm is a native of Japan and China and is related
to the Ulmus genus, which is the genus of the European and American
elms. It is deciduous with small ovate, serrated, pointed leaves and
smooth gray bark. It is a vigorous grower and is most often used for broom
and group plantings. Root-over-rock plantings are also common. The
gray-bark elm is considered by some to be the classic broom style
Lighting: Full sun to
part shade. During summer in southern part of USA, do not expose the tree
to direct sun during the heat of the day.
Temperature: Zones 5
through 8. Make sure the tree has good winter protection.
Allow the soil to dry slightly between waterings. Spray the foliage with
water daily during the summer.
Feeding: Feed every
20-30 days with a slow-acting fertilizer during spring and again from late
summer through mid-autumn.
If you prefer to use chemical fertilizers, feed every
other week using a half-strength solution of a balanced fertilizer such as
Peter's 20-20-20. If the fertilizer you use does not contain trace
elements (minors) then you may need to treat with chelated iron a couple
times a year.
Pruning and wiring: The gray-bark elm is usually shaped exclusively by pinching
and pruning, but wire can be used. Wiring may be done any time from late
spring (after the leaves are set) through mid-autumn. Structural pruning
is done in winter so that the tree will lose less sap and so that the
branch structure may be more easily seen. The foliage is developed by
pinching back the new growth during the growing season. Wait until new
shoots have at least 4 sets of leaves, then pinch back to 2 sets of
To reduce leaf size, healthy trees can be leaf pruned
in early summer. All of the leaves are removed, leaving only the leaf
stems on the branches. The tree will respond by putting out a second set
of leaves, smaller than the first set. Do not leaf prune the same year
that the tree is repotted.
To train a tree in the broom style, allow it to
grow (keeping the trunk straight) in a large pot or in the ground until
the desired trunk girth is achieved. Then cut off the tap root and lop off
the trunk above the point where you want the branches to diverge. Allow
the branches below this point to grow out some, then prune them back to
only a few internodes. Let the branches grow out again. In the spring
before the buds open, gather the branches up into a loose broom shape
using raffia. The new growth from the base of these branches will then
grow outward to fill out the broom shape. Repeat the process of pruning
and gathering as necessary to achieve the desired branch
Repot every 2-3 years in early spring. Prune the roots by up to half their
length. If the tree is in a shallow bonsai container, repot every 1-2
years to avoid having the roots push the tree up out of the
This tree is typically potted in a shallow bonsai pot
that is either glazed in cool (blue, green, beige) colors or is unglazed
in earth tones. Simon and Schuster's recommends 60% soil, 20% peat, and
20% coarse sand. Rémy Samson recommends 2 parts loam and 1 part coarse
sand. Peter Chan recommends 1 part loam, 1 part peat, and 2 parts coarse
Pests and diseases:
Pests: Pest resistance: long-term health usually not affected by
Diseases: Normally disease-free as it resists Dutch Elm
disease and Elm leaf beetle. Zelkova is subject to canker diseases
particularly if the trunk is repeatedly wounded. Avoid wounding and
maintain tree health.
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