BASIC HORTICULTURAL PRINCIPLES
Air is of course the source of carbon dioxide, which is needed by plants to produce food and it is just as important in the soil because tree roots, like leaves, need to breathe. If soil air is excluded as happens when soil is waterlogged, the roots suffocate and the tree will eventually die. The millions of micro organisms that live in the soil also need air; without it they too die and the soil becomes lifeless.
Most plants need soil in order to grow. Soil is the most important raw material after water. Soil should be made up of two ingredients, organic and inorganic matter. The organic material which is called humus is derived from vegetable and animal matter. The inorganic material comes from weathered rock. Different soils have differing amounts of humus and rocky substances. The geology of a region determines to a large extent the nature of the soil. Soils in a predominantly limestone region will be alkaline. Where the geology is volcanic, the soil will be slightly acidic. The size of the soil particles determines whether a soil is predominantly clay, loam, sand or stone. Soil that is made up predominantly of very fine particles is called clay, those that are predominantly composed of medium size grains are known as silt, while those that have the largest particles are called sand or grit.The spaces between the soil particles trap air and this is often referred to as the atmosphere in soil. The soil atmosphere plays a most important role in plant development. The roots of plants all require air in order to breathe and if air is not available the plant cannot grow. It should also be remembered that a soil will have in it millions of micro organisms and these organisms will need a constant supply of air and water in order to survive. There are some who advocate the sterilization of soils used for bonsai. This practice is highly dubious in my view because more harm than good can come of it.Sterilizing soil kills all
the beneficial bacteria and other micro organisms, leaving the soil virtually lifeless. Soil needs these microorganisms in order to break down the humus and thereby release the beneficial chemical elements. These elements are essential for healthy plant development.
BONSAI POTTING MIX.
A good Bonsai soil is rather a growing medium, as bonsai soil should not have any or very little soil. By Soil I refer to fine sand and clay. There may be a small advantage by adding soil to plants that require mycorrhizae, and mycorrihzae, being a beneficial
fungus is found in soil. Fine particles should be limited due to their compaction nature and water retention ability, which can damage restrict root development.
A trees roots requires water, nutrition and air. A good growing medium provides all of these requirements and more. Certain species will require more moisture and water retention properties, while others will want a different PH structure. It stand to reason
that your optimum mixture will depend on the species being grown, which goes back to the climatic condition wherein the tree occurs naturally. e.g. a swamp cypress from the Florida Everglades requires different condition to an Acacia from the dry bushveld.
The first component is sharp fine aggregate (sharp stone or sand of 2mm-5mm). The particle should not be able to fit together tightly, by leaving spaces for water air and nutrition. The particles should be inert and not be able to break down into clay. This
allows quick drainage, fine root growth and air into the soil.
The second major component should consist of fine sifted humus (compost) which is the required nutrition. The compost should be well composted as this will release higher quantities of nitrogen and carbon dioxide. Clearly the better the quality of nutrition, the
better the growth and the less the weeds.
By changing the percentage of organic to inorganic mixture as well as particle size and ph, one can change the whole mix.