why do we care so much about bonsai soil? After all, we can plant a tree in our yard and it grows fine. Why does the miniature version of that tree need special soil?
The answer lies in the roots of your tree.
Most first-time bonsai owners don’t think much about what’s inside their bonsai pot, as they’re more interested in the beauty of the tree itself. But that beauty can only sustain itself if the tree has a strong foundation. And that foundation are the tree’s roots.
When it comes to bonsai, we’re interested in developing fine, fibrous “feeder roots.” These roots consume the nutrients in the soil and feed the rest of the tree. Without a strong network of feeder roots, your tree will become weak.
Normal potting soil doesn’t provide an environment which encourages the growth of feeder roots. So we must consider a different type of soil for bonsai trees.How Can Bonsai Soil Encourage Root Growth?
Before we go into specific soil mixes for bonsai soil, let’s take a quick moment to understand the type of environment needed to grow strong, vigorous roots.
The roots of your tree require:
Air
Water
Nutrients
To provide those requirements, we need bonsai soil that has these properties:
Aeration
Drainage
Water Retention
Bonsai Soil Aeration
The roots of a bonsai need oxygen. If they are tightly packed in garden soil, it’s difficult for them to receive the oxygen they need. A loose bonsai soil that has room for fresh air to permeate between the particles provides proper aeration for the root system.
Bonsai Soil PileAn Example Bonsai Soil Mix – “Boon’s Mix” from Superfly Bonsai
Bonsai Soil Drainage
Think of a bonsai tree planted in garden soil in a small container. When you water it, that water will remain in the soil for several days, or even a week. During that time, the roots won’t access to the oxygen they need. Starving your tree of oxygen will weaken the tree.
Additionally, many bonsai trees don’t like “wet feet.” That is, they don’t like to soak in water for long periods of time. Over-watering a bonsai planted in garden soil can actually rot the tree’s roots. This “root rot” is detrimental to the tree and may eventually kill it.
A proper bonsai soil allows for excess water to escape through the pot’s drainage holes after watering bonsai.
Bonsai Soil Water Retention
As much as we need good drainage, we also need some water to remain. If we used actual gravel as the substrate, water would flow directly through the pot and out the drainage holes leaving no water behind for the roots to utilize.
Because of this, we need to include some type of material in our bonsai soil mix that retains some water.
