Page 21 - BSAM 2016 Q4

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 o that big bud at the end of the branch, the auxin factory is removed, and dormant buds and shoots take o 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 buds on a branch....the apical meristems. Smaller quantities are made in smaller buds. Auxin travels down the shoot and stimulates root growth. Along the way down to the roots, it inhibits the growth of smaller shoots as it travels down the branch, keeping dormant buds dormant. If we cut o that big bud at the end of the branch, the auxin factory is removed, and dormant buds and shoots take o and begin to grow. And that’s the beginning of rami cation for bonsai.
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 later- al shoot growth. It’s the ‘opposing’ hormone to auxin, and when these two hormones are in balance, than 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 in uence 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 o 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.
If we repot a tree in spring, what are we doing? Cre- ating a de cit of cytokinin. is results in a hormone overbalance in the favor of auxin, which results in root growth. Spring is a great time to repot, because emerg- ing buds, and the abundance of auxin created there, regrows the roots.
O en a er repotting a tree it’s best to wait a bit lon- ger than usual to cut back shoots, maybe as late as early summer, in order to use the auxin in those apical buds to regrow the root-system.
Generally speaking, heavily pruning a conifer dur- ing repotting time is not recommended, whereas pruning can o en be done with a deciduous tree. For the conifer, which has di culty rebudding on com- mand, a full canopy that is full of auxin and the ability to make sugar will regrow the root system.”
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