Bonsai Soil [The Best Composition for a Healthy Bonsai]

So you want to grow an amazing bonsai? Well, you need soil. But, what is the best soil for bonsai?

Bonsai can be grown in most soil, but bonsai soils are specially made to promote growth and maintain the plant’s health. The ingredients for a proper bonsai soil mixture contain different things depending upon the species of plant.

In this article, we’ll go over the different options for bonsai soils, including soil types, different growing mediums, and what is the best bonsai soil for you.

Demonstration of Proper Bonsai Soil – Courtesy Herons Bonsai

The Purpose of soil

The goal of a great bonsai soil mixture is to hold the nutrients so the plant can readily use them. Bonsai soil also is a conduit for the plant to soak up water and air. All three components are vital to the health of any bonsai plant.

Free-Draining Soil

One of the most important aspects of bonsai soil is that it drains easily. If the soil cannot drain and stores the water close to the plant’s roots, the plant will develop diseases and eventually rot. Further, this article details the different mediums that promote free-draining soil.

Securing the Plant

Another important thing soil provides to a bonsai is the ability to secure the tree in the pot properly. A firm yet free-draining soil will give the plant’s roots something to hold onto. This, coupled with the standard procedure of wiring the bonsai’s roots to the pot, will help your bonsai stay in place in its planter.

Different soil types

A great bonsai soil looks natural and provides the plant with everything it needs to grow into a mature tree. The following soil types are great options to consider for your bonsai.

The “Types of Bonsai Soil” diagram below shows the relationship between clay, silt, and sand. The combination of these three makes up different varieties of loam which is often used for bonsai soil.

Bonsai Soil Types - Illustration

Sphagnum Moss Peat

This material is gathered at the bottom of sphagnum bogs, where the material has been decaying for years. It is great for bonsai soil mixtures because it provides a fluffy, lightweight, and inexpensive option for ensuring the soil drains well.

Loam

Loam combines three materials: sand, fine clay, and silt. It is an inorganic mixture that further reinforces the bonsai soil’s quality through the loam’s various properties.

Grit

A great grit for bonsai soil measures between 1/8 – 1/4 inches in size. Grit is a crushed stone of different varieties. It strengthens your bonsai soil mixture, aeration opportunities for the roots, and excellent drainage.

Clay Granules (Akadama)

Often mined from volcanic areas in Japan, Akadama is an excellent medium for bonsai plants. It is used by many experts and provides aeration and ease for us.

When repotting bonsai plants, especially older specimens, it is important to mitigate root damage. Akadama is great because the roots do not bind to the material and easily shed the substrate while repotting.

Lava Rock

The best type of lava rock for bonsai soil is 1/4 inch. It provides an excellent, permanent area for the water to drain through the mixture, providing ample long-term health benefits for the tree.

It is an inert material that provides no inherent nutritional benefits, but other components of the mixture are designed to provide that.

Turface

This material has been used for decades by bonsai artists as a top-dressing component within bonsai soil mixtures. It is a high-fired clay, meaning it is tiny particles of clay that have been sent through an oven and heated to extreme temperatures. Because of this, it is inert and perfectly sterile.

An Expert’s Advice on bonsai soil

Bonsai are essentially container plants we’ve made look like small trees.  Because we ask these plants to live as long as they can in a pot, the soil is a major consideration. You can either mix your own or start by purchasing a basic bonsai soil mix.  Today, many hobbyists are using “soil-less mixes.” This just means they do not contain any earth or dirt. 

Remember: never use dirt from your yard for any potted plants.

Bonsai Soil Attributes

Of all of the bonsai supplies, the soil is arguably the most crucial. It’s important to know what a good bonsai soil composition looks like. Without the proper materials within your soil, your bonsai can be susceptible to disease.

  • Fast Draining – One of the reasons watering bonsai is so difficult to learn is the different types of soil bonsai are grown in. When watering, the water should run through quickly and come out of the holes in the bottom of the bonsai pot.
  • Water Retention – No matter the soil content, some moisture must be retained. Some components hold more water than others.
  • Aeration –Space between particles is important. This does not mean “air pockets,” which we always avoid.  It means the mix should not be so fine or wet, that it becomes compacted.

When purchasing bonsai soil online, remember to ask about shipping costs.

Container gardeners and plant nurseries grow in a vast number of soil mixes. Many use a very heavy, wet type of soil to prevent drying out so quickly. That does not mean the plant prefers this type of soil, only that it will survive in it for starter growing purposes. If you purchase a pre-bonsai plant in one of these heavy soils, eventually, you will need to remove it.

Once we create our bonsai and they are ready for bonsai pots, very heavy, extra fine, and/or muddy soils should be eliminated. Depending upon the plant species, it may be done gradually, or in some cases, it can be done all at once.

Remember, when it comes to soil, what someone else temporarily ‘gets away with’ may prove to be a killer in the long run.


Bonsai Soil Components

If you decide to make your own bonsai soil, remember all components should be free of dust and be similar in size. This can be resolved with sifting and rinsing. (Dust and very small particles can clog the drainage.)

Try using one of each – organic and inorganic. 

Discover which works best for you and your bonsai. Never repot all your bonsai in a recommended mix without testing it first.

Organic

Some people use peat moss to add acidity to certain plants. However, it retains a lot of water and should be used sparingly.

“Potting soil” from garden centers is a last resort for organics and should only be used with the addition of an inorganic aggregate.  If you choose to purchase potting soil, do not buy the cheapest!  It will most likely be the wettest and heaviest, which is what you do not want!

Inorganic

Pebble mix

You will hear about many seemingly odd materials to add to your mix, including ‘chick grit’ (a crushed granite available in farm feed stores) and ‘kitty litter’, a type of calcined clay, as well as imported akadama clay.

Used properly, they all work. Lava rock and pumice are other additions used with good results. Overall, a good mix looks like small gravel!


 When you purchase a bonsai, the topsoil you see may or may not be what it’s growing in.  Take a chopstick and dig down a little to determine the actual soil.  If any gravel is glued on, remove it immediately for better drainage.   

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