Let’s set the record straight, there is dirt, there is loam, and then there is Bonsai Soil. These are not at all the same thing. Most dirt is just that, a combination of many things, rocks, debris, clay, and sand. Dirt is not a very good medium for planting a Bonsai tree or for that matter any tree or plant. Loam on the other hand is a mixture of clay, sand and silt. Loam is sometimes supplemented with organic materials. But even with this added organic material, it still is not the best medium for planting a Bonsai tree.
Common dirt is too fine of a material for a Bonsai tree. It tends to compact over time, and doesn’t provide good drainage. Common dirt will become sodden over time, which leads to root rot and other fungal disease. The problem with loam, is the clay content. The planting medium used for the Bonsai must be able to drain, clay doesn’t drain. This lack of drainage can cause the same problems as the common soil.
So what is Bonsai soil? A real good question that has many answers. Bonsai soil is a mixture of planting mediums that are made of particles that allow drainage, while supporting the tree. Good Bonsai soil will have three main essential components. The soil must be to drain immediately. Water should not stand on the top of the soil. The second essential component of good soil is aeration. Aeration is having particles that are large enough in size to create air spaces between each particle. These spaces are essential to allowing the tree roots to breath. Soil contains both air and water particles Too much of either component is bad for the tree. Poor drainage is an over abundance of water and a lack of air particles, dry soil is just the opposite, an abundance of air and not enough water.
The third component of good Bonsai soil is the ability to retain enough water to ensure the survivability of the plant until the next watering. While the issue of drainage and water retention seem to be in opposition to each other, it’s important to understand that there must be a happy mixture of both. Too much or too little of either is bad.
A good Bonsai soil is a blend of both organic and inorganic materials. Organic materials such as peat, or dead plant matter or bark from the tree. These materials have a tendency to continue to break down and become compacted over time. Inorganic materials such as volcanic lava or baked clay, tend to retain their open structure and do not become compacted. Because of the nature of both materials, a good mixture of both is essential.
The quality of the soil will have a profound effect on the vitality of your Bonsai tree.