Defoliating
or leaf-cutting is a technique that involves removing the leaves
of deciduous and broadleaf bonsai during the Summer; it forces
the bonsai to produce a replacement set of leaves in a second
'false' Spring flush of growth. This replacement set of leaves
results in increased ramification and leaf density, a reduction
in leaf size and internode length and finally, superior Autumn
colours.
A
Warning about Defoliation
Many enthusiasts
first try defoliating on trees that are not horticulturally and/or
aesthetically ready for defoliation.
Before describing defoliating techniques in detail, it is worth
highlighting the need for trees to be healthy and vigorous before
leaf-cutting is carried out. The removal of the leaves from a
tree is debilitating and will temporarily weaken any bonsai; defoliating
should only ever be carried out on vigorous specimens that will
be able to recover from the process. Trees that are showing signs
of weak growth, whether it be due to recent repotting, disease,
styling or recent hard pruning, are not suitable for defoliating.
Be aware that defoliating can be so taxing on a bonsai that failure
to respond can occur if the tree is not vigorous; parts of the
branch system can be weakened to the point that they die-back.
Defoliating is also a technique intended for 'finished' bonsai
only; a tree intended for defoliation will have the trunk, primary,
secondary and tertiary branches established. Defoliating a tree
that requires branch or trunk building will slow down development
of these parts greatly.
Different tree species react in a variety of ways to defoliating;
some respond quickly and strongly to total defoliation (to the
extent that they can be defoliated more than once a year) while
with other species it is preferable to only partially defoliate.
The most common
way to defoliate a tree is to remove each and every leaf with
scissors, leaving the leaf-stalk or petiole behind. The remaining
petioles nourish the tree as new buds contained within the leaf-axils
begin to extend and open out. As the new leaves start to open
out, the petioles dry out and fall away from the branches.
After defoliating a tree, leave it in good light to stimulate
stronger budding, particularly from inner and lower branches.
Without leaves, a defoliated bonsai will require less watering.
The new leaves start to emerge 3-6 weeks after defoliation (depending
on the exact timing, tree vigour and tree species) and are smaller
and more numerous. Vigorous trees will also back bud as a result
of defoliation.
The exact timing of defoliation differs from one tree species
to another. As a very general guideline, leaf-cutting can be carried
out after the spring flush of growth has hardened off (the leaves
lose their spring colour and become more 'leathery'). For more
detailed timing notes please see the specific species guide later
in this article.
Immediately after total defoliation, the tree is bare for the
first time since Spring and it is possible to study the branch
structure; this is an ideal time to prune, wire and style a deciduous
tree.
Partially
defoliating a bonsai is much kinder and with some tree species
is preferred to total defoliation. Large leaves (or the largest
leaves) are gradually removed through the growing season until
late Summer, these large leaves are slowly replaced by smaller
leaves as and when required.
There are several advantages to partial defoliation; the stress
of leaf removal is spread over a number of weeks or months. The
largest leaves tend to be in the strongest, most apical areas
of the tree (that is, the tips of the branches, particularly in
the crown or apex) and their removal enables light to reach the
weak, inner and lower branching. In this way, partial defoliation
can be used as a means to reinvigorating the weaker, lower areas
of a tree by weakening the apical areas.
Species
suitable for defoliation techniques
This list
by no means complete; other species can be defoliated but I would
strongly suggest that unless a particular tree species is recommended
for total defoliation by an experienced enthusiast, first try
a limit amount of partial defoliation on a specimen to gauge its
reaction to defoliation techniques.
Defoliation
is normally carried out around midsummer in the UK; however some
species are best defoliated a little earlier in late May, the
others in mid June. Please note that different climates and differences
in the length of growing seasons will alter the optimal time to
defoliate according to where you live.
Species
to be defoliated in May
Crataegus
species Hawthorns:
Total defoliation in May but partial defoliation of larger leaves
is normally adequate.
Fagus sylvatica
European Beech:
Partially defoliate larger leaves from May. Complete defoliation
has varying degrees of success and is not recommended. For further
details please see Advanced
Pruning Techniques for Beech/Fagus
Quercus robur
European/English Oak:
Partial defoliation of all large leaves from May onwards except
those on weak (often low) branches. Thin out leaves (leaving one
or two on each branches) in heavily congested areas of the tree,
often at the tips of branches.
Sageretia
theezans: Total defoliation can be carried out before June and
with very vigorous trees, a second time after midsummer.
Ligustrum
sp./Privets: Total defoliation can be carried out before June
and with very vigorous trees, a second time after midsummer.
Ulmus various
species Field Elms:
Total defoliation in May; also helps combat thickening of the
tertiary twigs that cane be a problem with Field Elms; particularly
for mame and shohin sized trees.
Ulmus parvifolia
Chinese Elm:
Total defoliation in early May can be followed by a second total
defoliation after midsummer if tree is vigorous enough. With only
a small leaf-stalk and huge numbers of leaves even on mame sized
bonsai;rather than cutting with scissors, remove leaves with fingers,
pulling away in the direction of the branch to avoid damaging
the new bud or branches.
Species to be defoliated in June
Acer palmatum
Japanese Maple:
Total defoliation in June is excellent for increasing ramification
and reducing leafsize. Partial defoliation of large leaves recommended
for the weaker red-leaved Acers.
Acer buergerianum
Trident Maple:
Total defoliation can be carried out twice a year on vigorous
specimens.
Carpinus Hornbeams
Total defoliation of only the most vigorous specimens. Otherwise
partial defoliation as per Fagus/Beech
species.
Fuchsia species
Fuchsia
Total defoliation can be carried out twice a year in vigorous
specimens
Malus Crab
Apples:
Total or partial defoliation.
Zelkova serrata
Zelkova
Partial defoliation of all but the weakest branches can be carried
out.
