Page 21 - Tạp chí bonsai cây cảnh BCI 2017Q2

Top left; Auxin is made in large
quantities in the big end
buds on a branch....the apical
meristems. Smaller quantities
are made in smaller buds.
Top right; If we cut off that big
bud at the end of the branch,
the auxin factory is removed,
and dormant buds and shoots
take off and begin to grow.
Middle left; Auxin travels down
the shoot and stimulates root
growth.

Middle right; Cytokinin is
produced in the roots. If there
is enough cytokinin—when
there are a lot of roots—it will
travel up the tree in the xylem,
and stimulate lateral shoot
growth.
Bottom; Heavily pruning a
conifer during repotting time
is not recommended, whereas
pruning can often be done
with a deciduous tree.

Auxin is made in large quantities in the big end If we repot a tree in spring, what are we doing? Cre-
buds on a branch....the apical meristems. Smaller ating a deficit of cytokinin. This results in a hormone
quantities are made in smaller buds. Auxin travels overbalance in the favor of auxin, which results in root
down the shoot and stimulates root growth. Along growth. Spring is a great time to repot, because emerg-
the way down to the roots, it inhibits the growth of ing buds, and the abundance of auxin created there,
smaller shoots as it travels down the branch, keeping regrows the roots.
dormant buds dormant. If we cut off that big bud at Often after repotting a tree it’s best to wait a bit lon-
the end of the branch, the auxin factory is removed, ger than usual to cut back shoots, maybe as late as
and dormant buds and shoots take off and begin to early summer, in order to use the auxin in those apical
grow. And that’s the beginning of ramification for buds to regrow the root-system.
bonsai. Generally speaking, heavily pruning a conifer dur-
Cytokinin is produced in the roots. If there is ing repotting time is not recommended, whereas
enough cytokinin—when there are a lot of roots—it pruning can often be done with a deciduous tree. For
will travel up the tree in the xylem, and stimulate later- the conifer, which has difficulty rebudding on com-
al shoot growth. It’s the ‘opposing’ hormone to auxin, mand, a full canopy that is full of auxin and the ability
and when these two hormones are in balance, than to make sugar will regrow the root system.”
shoot and root growth is in sync. An overabundance
of cytokinin creates shoot growth; overabundance of
auxin creates root growth.

Hormones and the Bonsai technique
How then does bonsai technique influence these
hormones, and consequently, how our trees look? If
we let a tree grow naturally, it’s in hormone balance.
And if we can have hormone balance, we can also have
hormone imbalance. Most of bonsai training—all
the tweaking, cutting, pruning and the timing of all
that—creates a growth response because of hormone
imbalance.
If we cut a branch off a satsuki azalea, what will
happen? Lots of shoots will arise from the cut site and
maybe down the branch as well, because we’ve created
an absence of auxin and an overload of cytokinin, and
both imbalances together grows new shoots.

April/May/June 2017 | BCI | 19