Bonsai
are ordinary tree species that require regular pruning to keep
their diminutive shape. Without pruning, branches extend and the
tree begins to lose its shape. Given enough uninterrupted growth,
these branches can eventually thicken out of scale with the trunk
and become coarse. Eventually, if left unpruned for long enough,
a bonsai will simply revert to resembling an ordinary tree or
shrub and the process of bonsai will need to be started again.
To
combat this reversion and to keep its shape, a bonsai must be
pinched and/or pruned on a regular basis. This is commonly referred
to as 'maintenance pruning'. The period between carrying out maintenance
pruning on a bonsai very much depends on the species used, the
time of year and the vigour of an individual tree. Identifying
whether a tree needs to be pruned though is simple, and will be
discussed in the following series of articles.
These
articles are written as a guide to the maintenance pruning of
'finished' or styled trees; there are however, occasions where
uninhibited growth is allowed. This is often required as 'sacrificial
growth' to thicken up trunks or simply in order to form a new
branch or branch structure.
Apical
growth
One
of the key elements to understanding the pruning of bonsai is
'Apical dominance'. Almost all trees and shrubs, and therefore
bonsai, are apically dominant. Essentially, this means that growth
is stronger near the top and outer edges of the tree. Apical dominance
is a mechanism that trees have evolved to use to encourage extension
of height and width, in order that the tree not be shaded out
by neighbouring plants. It also enables a wider distribution of
seed in Autumn so that their seedling offspring are not in direct
competition with the parent tree for light and water.
A
result of apical dominance is that foliage nearest the trunk is
eventually shaded out and dies back. This inner growth is lost
at the expense of the ever-extending apical growth. Normally when
growing in the wild, a tree will waste little energy forming new
growth on its inner branches; it will concentrate all of its resources
on the tips of the branches in its continual path onwards and
upwards.
Unfortunately
for bonsai enthusiasts, unless something is done to halt the apical
tendency of their trees; the inner and lower branches become bare,
with pads of foliage concentrated at the tips. Lower branches
will lose vigour and eventually die at the expense of the more
vigorous upper-branches. As importantly, a well developed bonsai
will exhibit branches that are thickest at the base of the tree,
with the branches becoming thinner and more refined as the eye
travels up the trunk to the apex. If apical dominance is not countered,
the upper branches quickly thicken up as a direct result of their
vigour and become out of scale with the weaker lower branches.
Using
these basic outlines of a bonsai, it is possible to see both the
effects of apical growth, also the way that pruning should be
carried out to counter it. Bonsai cannot be simply be pruned to
the same degree on each and every branch. In the first diagram
of an unpruned tree, it is possible to see that the predominant
growth is around the apically-dominant areas, around the crown
and outer branches. To not only re-shape to a mature form but
to also counter the apical dominance, the tree is pruned harder
nearer the top and sides than it is lower down the trunk. As can
be seen in the second diagram, this results in pruning the tree
into a roughly triangular shape.
Pruning
this way means that the otherwise weaker inner and lower growth,
is left with more foliage and more vigour than the now weakened
apical areas. This results in a far better distribution of energy
throughout the tree as well as improved form. The effects of this
pruning will not last that long though; within a relatively short
period of time the upper and outer areas will recover their dominance
and this again will need countering.
The
timing and manner of pruning a bonsai is discussed in the following
parts of this article.
Pruning
Deciduous Bonsai
Pruning
Coniferous Bonsai
