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Hormones

By Lionel Theron

Things are seldom quite as simple as they seem at first glance and this also applies to the manner in which plants behave. However, for many of us the fact for example, that plants turn towards the light is all we need to know so that we will rotate our bonsai in order that they do not become overly one-sided. We do not need to know that hormones are stimulating cells to elongate on one side which then causes the plant to slowly turn towards the light. This is nevertheless interesting to the searching and active mind ....

There are growth substances (hormones, phytohormones) which have a marked effect on plant growth when present in very low concentrations and conversel y, the absence of such substances have an inhibiting effect or even a detrimental effect on plant development. Some of these substances are produced within the plant. Ahnormal growth or even death may result from the unusually high or low concentrations of a growth substance. This reaction is exploited in weedkillers, for example, which are often based on synthetic auxins, a growth hormone synthesized in shoot apices.

Normal growth is only achieved when there is a correct balance of the various growth substances and in recent years various products have been developed which have beneficial results on plant growth. Two examples are KELPAK and SUPERTHRIVE. These products are of little use on their own; both macro and trace elements should still be used in a feeding program for plants - they do not replace fertilizers!

Some examples of hormones are described as follows:

AUXINS

A group of growth substances synthesized mainly within the merestematic regions and associated with the promotion of elongation of shoots and roots. These substances promote root initiation and are used in the so called "rooting compounds".

CYTOKININS

The primary effect of cytokinins is to stimulate cell division. There are correlations between auxins and cytokinins, as indeed between all hormones, and the balance between the various growth substances stimulates different effects.

GIBBERELLINS

Gibberellins are mainly associated with the greatly increased elongation of stems. Giberrillic acid is used where plants are manipulated to produce flowers or fruit in a particualr season or to discourage the development of seeds in fruit, but this is also a growth regulator.

ABSCISIC ACID

Associated with leaf and fruit abscission and control of dormancy. This substance causes leaf drop in distressed plants due to, for example, the lack of water and it attempts to prevent excessive transpiration. This substance is what causes leafdrop in autumn in deciduous plants.

ETHYLENE

The production of ethylene, a gas, is frequently stimulated by auxins and causes radial expansion in cells. It promotes flowering in certain species of plants and induces the production of root hairs and stimulates seed germination.

In conclusion, I have attempted to illustrate the importance of growth hormones. Much interesting work is being done on the subject especially in the USA and various useful products are the result of this research.pyracantha

Some of these, which are locally available, could benefit your bonsai. These products are ROOTONE (a root promoting hormone powder useful in cuttings and air layering), weedkillers, KELPAK, and SUPERTHRIVE.

I have not mentioned vitamins, which also seem to have some importance in plant behaviour. Many vitamins are synthesized by plants, but not so with the B range of vitamins. These are mainly animal products, but they are also useful in horticultural pursuits where they may be used in preetransplanting to prevent trauma - it works, but that is the subject for another occasion ...

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Random Bonsai Tip

If your trunk lacks taper split the base of the trunk from below and plug the ends open with a piece of wood or a small stone.