Crushed Lava Rock

Bonsai Soil is a hotly debated subject amongst bonsai enthusiasts. I know somewhere, someone will take exception to what I write here, but I don't claim to have all the answers. Instead, consider this as help in getting you to ask better questions. I'll share what my clubmates use and what I use. You can take it from there.

In nature, trees can and do grow in a variety of environments and substrates. However, the majority grow in what we might call your garden variety dirt.

Soil, in the wild, provides everything (mostly) that trees and plants need to thrive. So it would seem like common sense to use this very thing in our bonsai pots so that our trees may also benefit from its wonderful properties. But there is a problem with that.

You see, a bonsai pot is a contrived environment that barely resembles natural growing conditions for a tree. While we strive to keep our trees as healthy as we possibly can, giving them what they have in nature does not effectively provide that.

For one, moisture in a pot gets locked in because of the heaviness of the soil. While this may be okay for a day or two, eventually this over-saturation can harm your tree. Roots need oxygen and common dirt in a pot makes it difficult for them to get it. In nature, the force of gravity takes care of that, but in a pot that effect is greatly reduced.

Turface MVP

Another point is soil compaction. While at first common dirt holds too much water, eventually it actually does the exact opposite. As soil settles and gets compacted into the pot, it becomes harder and harder for water to permeate it. Without water the tree eventually dies.

In a nutshell, do not use normal potting soil.

So what should you use for your bonsai soil. Well, there are a number of materials regularly employed and, depending on who you ask, any one of them may be considered good or bad, right or wrong. Consider these points

The first and most important rule of a good bonsai soil is it must be fast draining. When you water your trees, the majority of the water you pour in should quickly drain out the bottom leaving just enough in the pot for the tree to drink from.

Second rule is to have particles of roughly 1/8 to 1/4 inch in diameter. This is just about the optimum size for holding enough water and allowing for great aeration for the roots once the water has run through the soil.

It's for these reasons that hard, inorganic material is the preferred way to go when choosing your soil ingredients. Some people use a mix of different materials using some organics and inorganic material. I prefer to stick with the inorganic.

There are exotic materials shipped all the way from Japan like Akadama and Karuma soil. People will tell you that this is the best stuff available anywhere and that there is no substitute. I don't buy that. The Japanese use this because it's what they have available locally. That's it. You do the same. Use what you have locally.

Many of the local bonsai nurseries here use a mix of crushed lava rock, hard clay like Turface, and maybe even decomposed granite. Some will mix in a little pine bark. It doesn't hurt. But I'm a practical guy and getting all these materials can be difficult and expensive. So I have cut it down to using one ingredient... Turface MVP.

Turface Close Up

Turface is the brand name of a sports field dressing material that you can find in some landscape and lawn care specialty stores. I get it from Ewing Irrigation in Sanford. It's cheap and works extremely well.

It's important when using Turface that you use the MVP and not any of the other products sold under the same name. Although the material is the same, the particle sizes are very different and will not work very well for this purpose.

It's doesn't hurt to mix the materials I have listed here, but as I said, it's not really necessary. I will say this, the lava rock adds a very nice look to the pot that Turface alone will not replicate. And if there is one thing that can't be denied, is that bonsai is all about style.