The use of specialized bonsai soil mixes is an important part of practicing bonsai. This beginner’s soil primer dishes all the dirt on bonsai soils! It covers the whys and hows, then wraps up with some simple soil advice to help as you create your own bonsai masterpieces.

While bonsai soil is an important and specialized component of the hobby, it’s nothing for beginners to feel anxious about.  Bonsai soil mixes are like making chili. Everyone has their own special recipe, and most of them turn out pretty well!

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Why do bonsai need special soil? 

Because bonsai reside in small pots, they must develop a fine, compact root structure to support the tree’s top growth. The special soils used in the practice promote the growth of a fine, healthy root system. They also promote good water drainage which is important for root health.

How is bonsai soil different from regular soil?

Potting soil or dirt dug from the ground tends to be composed of fine particles with a consistent structure. Its characteristic dark brown or black color comes from a high proportion of organic matter. The organic components, along with the soil’s structure, slow down drainage and help with water retention. 

Bonsai soil compositions focus primarily on inorganic materials.  Course in appearance, bonsai soil can be described as gravely, rocky, or gritty. The larger particle sizes of the inorganic components promote drainage, while a small proportion of organic matter retains water. Most mixes incorporate only small amounts actual dirt or soil, or they use a different type of organic matter. Bonsai soil can vary in color and composition, depending on the type or types of materials in the mix.

What makes a good bonsai soil?

A good bonsai soil must do two things:

• The soil must drain quickly so that the roots do not sit in water for extended periods of time.  Roots need to breathe oxygen to stay healthy, and soil that is too wet promotes disease and root rot. 
• The soil must retain enough moisture between waterings so that the roots can absorb and deliver moisture and nutrients to the top growth of the tree. 

To achieve this important balance, a typical bonsai soil mixture contains at least two ingredients – some form of organic matter and some form of inorganic matter or grit.  

Organic matter provides nutrients and helps retain moisture so the plant doesn’t dry out as quickly. Commonly used organic matter includes peat moss, humus, composed tree bark, leaf mould, loam and even potting soil. 

Grit, or inorganic matter, allows the soil to drain, helps create air spaces so the tree’s roots can breathe, and adds weight to the soil, helping anchor the tree in its pot.  Gravel, crushed granite, crushed volcanic rock, chicken grit, sand, and specialized products such as Turface and Akadama are favored sources of grit among bonsai enthusiasts.

Clay kitty litter with no chemical additives used to be a common ingredient in many mixes, but has declined in popularity.  Kitty litter tends to break down quickly and better alternatives are more readily available now than in years past.

What is the right soil for me?

The “right” soil is the one that works best for you and your tree in the spot where it lives. For example, say you have a weeping willow bonsai, which tends to like a somewhat moist soil. In addition, you live in a warm climate and the backyard where you keep your tree faces south – both conditions that will dry the pot out faster.  Also, say you live a hectic life, work long hours and only have time to water once a day.  You would probably want to incorporate some extra organic matter in your soil mix to hold moisture longer between your daily waterings.

How do I get bonsai soil?

Today’s hobbyists have the good fortune of being able to purchase pre-made soil mixes from a variety of retailers or obtain soil the traditional way – mix it themselves!

I recommend that beginners take the easy route and purchase a quality soil mix appropriate for the majority of plants. A couple to consider are the Bonsai Jack 221 mix and the professional bonsai soil mix from Superfly Bonsai. The smaller size trees that most beginners start with don’t use a large volume of soil, and several can be potted from a gallon bag. 

Buying pre-mixed soil saves buying individual ingredients in bulk and storing the leftovers. However, for those who want to mix their own soil, there are a variety of recipes that practitioners have reported good results from using – remember the chili analogy? Here’s one that uses just a few ingredients which can be sourced easily and inexpensively:

4-Ingredient, 10-cup Soil Mix