How to make bonsai tree Soil Mix

The basic composition of soil is that it is mineral 45% and 5% organic matter which is leaves and humus and bark and all tree waste. The other 50% of the soil is 25% water and 25% air. Now remember this because later on, it’s going to be crucial in the development of your bonsai. In nature the organic matter and mineral matter is kind of fixed to some extent. The organic matter comes from the trees themselves so they are self cycling, but in a bonsai pot, the organic matter depletes quite fast, so we have to provide organic matter to fertilize it. But remember, for bonsai purposes, we use soils that are more or less sterile and we provide the feed. Coming to the soils themselves, they are defined depending on the size of the grain in the soil. When you look at the cross section of soil, you see that the soil horizon, as it is often called, the top two inches is where most of the decaying matter is, and then between 2 inches and 10 inches is where the soil is the richest. So most bonsai roots or most plant roots are within the first 10 inches because of that. All the soil level below that, below the 10 inches up to 30 inches, up to 40 inches, 48 inches is varying depths of richness from the soil. Between 30 and 48 inches, the soil is more or less depleted. When you feed fertilizer to the soil, the soil has got to be able to absorb it and hold it and release it to the tree as and when it is needed. And then finally, it’s got to be able to drain well so the water, in nature, the water tends to follow the top and then drain away. It doesn’t linger by the roots. So in Bonsai pots, we’ve got to do the same thing. We got to have the water draining away so that when you water it, the pot gets soaked initially. The soil absorbs all the water that it needs and surplus is let go. It drains away. So the soil that we choose for bonsai needs to do these things. We tend to use traditional Japanese bonsai soil. Akadama, which is by far the most popular. Akadama is sun dried organic substrate clay. We then have Kanuma, which is acidic soil which is for lime hating plants, and then we have Fuji grit. Now the grit in the bonsai soil helps with multiplying bonsai roots, the fine roots. Then there is another thing called Keto. Keto is used used primarily for building borders around landscapes or roots over rocks. We can use more or less any modern growing medium. The horticultural world tends to use mola or seramis which is another clay that’s been fired. We can use readily available pumice and expanded clay which is fired clay which are quite hard but they’re very porous and they hold a lot of water and air. We have two sizes that we generally use. Between 3mm and 6mm for deciduous trees and between 6mm and 9mm for all pines. We use it in the ratio of two parts Akadama to one part of pumice. You could, of course, use two parts Demelin and one part of pumice, or two parts ceramic and one part of pumice. That’s up to you.

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