To Feed or What to Feed

by Lionel Theron

Plant nutrition is fairly complex, a brief and hopefully helpful resume follows here. Plants require 16 elements to sustain healthy growth and a deficiency in anyone of these will be reflected in various ways. The elements are:

  1. Carbon, Hydrogen, Oxygen these are absorbed from the air and water.
  2. Nitrogen, Phosphorus, Potassium - macro elements, indicated by the symbols on commercially available fertilizers e.g. 2.3.4 (24). The (24) indicates the percentage of those elements in the fertilizer. The balance is made up of the carrier and possibly smaller quantities of micro element.
  3. Calcium, Magnesium, Sulfur Microelements which are required in relatively larger amounts.
  4. Boron, Chlorine, Copper, Iron, Manganese, Molybdenum, Zinc - these micro elements are required in very minute quantities. Chlorine is nearly always in abundance as it is difficult to manufacture fertilizers without producing chlorine as a by-product. In any event most water supplies contain large amounts of chlorine.

As bonsai are grown in small containers with relatively open (porous) growing medium, the nutrients leach out rather rapidly and consequently should be replaced frequently. This includes the micro elements as well as the macro elements. In addition to these elements hormones and vitamins play a role in the health and development of the plant.

Certain soil mixes, which have been tested often, showed deficiencies in Phosphorus, Potassium and Magnesium and these may also be added in the following forms:

Bone meal, hoof and horn meal or super-phosphate;

Granite chips rich in potash or wood ash; Magnesium sulfate.

The three elements available from the air or water are usually readily available. Bonsai which are occasionally dunked in water to above the soil level, until the bubbles stop coming up, benefit by the water replacing the gases in the soil and then when the water drains out it is replaced by fresh air into the gaps in the soil. This fresh air also contains oxygen, which the plant takes up through its roots.

Most of the 16 elements do not work in isolation, but in conjunction with one or more of the others, e.g. a deficiency of iron blocks the plant's ability to take up available nitrogen; also boron and molybdenum operate together. We can broadly analyse each element's function, but it should still be borne in mind that balanced applications are usually what are required.

Deficiencies of any of the elements manifest themselves in recognizable symptoms and can very often be diagnosed by experienced plantsman. In order to obviate problems it is possibly best to follow a feeding programme that is balanced in such a way that all contingencies are catered for.

An example of a feeding programme would be to use a fertilizer containing all the macro and micro elements such as Nitrosol (a balanced organic fertilizer) alternating with a chemical macro element preparation such as 2.3.4 These could be applied at fortnightly intervals in summer and less frequently in winter.

If it is necessary to tum a tree a dark healthy green in a hurry a little urea or limestone ammonium nitrate (LAN) may be used with caution, as high quantities of nitrogen rich fertilizer may bum plants. There are dozens of good fertilizers and feeding programmes suggested (as well as a few unscientific and poor ones) so the example above is merely a suggestion. It is always possible to ask experienced bonsai growers for help and advice, which they are usually only too happy to give. Reputable bonsai nurseries have to be in possession of sound knowledge to enable them to grow healthy, saleable trees and they are generally also pleased to help the potential customer.


Things are never quite as simple as they seem at first glance, the same applies to the manner in which plants behave. Plants turn towards the light and it is useful to know this fact, as we can rotate our bonsai in order that they do not become overly one-sided. The reason why plants face a certain direction is due to the phyto-hormones that stimulate cells on one side to elongate thus causing the plant to slowly tum towards the light. This is one of the numerous examples of hormonal effects in plants. There are many such phenomena and it is sometimes useful to know something about them. It may aid us in helping our bonsai give us more enjoyment.

There are growth substances (hormones and phyto-hormones) that have a marked effect on plant growth when present in very low concentration. Consequently 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. Abnormal growth or even death may result from the unusually high or low concentrations of growth hormone. This reaction has been exploited for example in weed killers. Weed killers are based on synthetic auxins (a growth hormone). Auxins are synthesised by plants in their shoot apices.

Normal growth is only achieved when there is a correct balance of the various growth substances. In recent years various products have been developed which have very beneficial results on plant growth. Two examples are Superthrive and Kelpak. These products have limited benefit on their own and both macro and microelements should still be used in a feeding programme for plants; they do not replace fertilizers. Especially useful are the development of commercial substances to promote rooting such as Dip-n-Grow and Superthrive which are a complex mix of hormones, vitamins and trace elements which prevent

stress in newly planted plants and stimulate growth and recovery of plants due to shock.


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 particular 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 leaf-drop 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.


Vitamins have some importance in plant behaviour and many are synthesized by plants. Plants do not materially synthesize the B group as they are mainly of animal origin, but are still useful in horticultural pursuits. They are frequently used in pre- and post transplantation to prevent trauma, with excellent results. Superthrive is the most well known product by which hobbyists and professionals swear.

This resume is merely an outline of the complexity of this subject; there is much more detailed information available in the literature, but for our purposes understanding the basics of feeding will ensure healthy trees.

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Random Bonsai Tip

When you have too thin trunks, you could twist two or three saplings together, fasten them together with wire and allow them time to fuse; or graft two trunks together.