Well Draining Soil for Bonsai Trees

Are you using the best soil for bonsai? The answer lies in the soil’s drainage.

While a lot of plants love dense, rich organic soil, bonsai trees need a mix of good soil and grit to allow water to be helf BUT also drain away without the roots rotting.

What does that look like? Let’s break this down in this article.

In this post, you’ll learn the perfect bonsai tree soil recipe and where to buy the components.

I do most of my bonsai gardening in containers, both indoors and outdoors, rather than in the ground.

Selecting soil for these containers can be a challenge.

Over the years, I’ve done a lot of research about the best type of soil for bonsai tree container gardens, I’ve tried quite a few approaches, and found that some of them work much better than others.

In fact, I’ve learned that, while improper watering of bonsai trees is a major cause of bonsai deaths (learn how to water properly here), the correct soil is a much bigger contributing factor than people realize.

What Is “Good” Bonsai Tree Soil?

Let’s start by talking about what you should be looking for in bonsai soil.

The best soil for bonsais in pots will hold enough water for them to absorb what they need but still dries out quickly so the roots won’t rot.

Bonsais absorb water from the air around them, not through direct contact.

Constantly sitting in wet soil causes their roots to rot, because they get too much water–eventually, the cells in the roots and leaves fall apart, causing the plant to die.

Several environmental factors can cause soil to dry out, so different types of soil will be best-suited for different growing areas.

The area where you live, as well as the location where you keep your bonsai trees, will play a role in determining what type of soil your bonsais need.

The Perfect Indoor Bonsai Soil

As mentioned earlier, I grow a lot of bonsais indoors. Since indoor environments don’t offer as much air circulation around indoor pots, I’ve found that using the right soil is extremely important for the health of indoor bonsais.

I highly recommend using soil with large particle size, roughly 1/4″ or 6mm. I learned all about particle size, and the role it plays in well-draining soils, by reading various forums.

One article gave a recipe for soil that works extremely well for indoor bonsais. I used to make the soil myself (since it was not available pre-mixed). The recipe combines:

1 Part Pine Bark Fines

1 Part Turface (an absorptive rock)

1 Part Crushed Granite

Why it works

Bonsai trees will grow in a variety of soils, but I want to go over why this soil works and why you should use it.

The pine bark provides an organic element and holds water–but it has air pockets for ventilation. As a bonus, it takes a long time to break down. The Turface absorbs some of the water and slowly releases it.

Crushed granite allows the water to flow among all the particles in the pot. Since the mix is very porous, water flows out easily. Plus there’s plenty of air, which means the roots are not left sitting in soggy soil or pool water like traditional potting soil.

The really crucial part of the recipe, though, is to make sure all the particles are roughly 1/4″ in size. It’s a lot of work to screen gallons of soil to get uniform-sized particles!

Pre-mixed option

Mixing this soil recipe myself was time-consuming and quite a challenge. But you’re in luck! You can now buy a ready-to-go bag of this soil from Bonsai Jack.

He’s an expert when it comes to soil, and this mix in particular is amazing for bonsai trees.

The particle size and consistency of the Bonsai Jack mix are exactly right for indoor bonsais. For example, while Turface is usually only available in 1/8″ particles, Jack has been able to get a 1/4″ size, specifically to use in this mix.

I highly recommend using this Bonsai Jack Bonsai Soil for your indoor bonsai trees. Especially if you tend to overwater, this soil will help your bonsais thrive!

However, if you’d rather not purchase this “gritty mix” online, it is possible to make it yourself. You should be able to find the ingredients at most nurseries.

Turface is also found at most auto parts stores as a product called “Oil-dri,” which mechanics use to clean up oil spills.

If you don’t have access to these exact materials, you can substitute other ingredients. Just keep in mind the ratio of inorganic to organic material needs to stay the same.

For example, if you use another type of bark, make sure you mix in another type of rock (such as pumice) as well. The really critical piece, as I mentioned above, is to ensure that the particle size is always roughly 1/4″ or 6mm.

Soil for Outdoor, Potted Bonsai Trees

If you’re growing bonsa trees outdoors, on the other hand, the Bonsai Jack Bonsai Soil may or may not be the right fit for you.

Since most of my bonsai experience has been in Queensland, where the weather is generally quite dry and hot in the summers, I found that using the Bonsai Jack mix worked fairly well outdoors, but it required me to water my bonsais more regularly, sometimes in a hot summer, this could be every other day.

I’m not great at remembering to water, so this mix required too much maintenance for me. Instead, I’ve been using a mix of Coconut Coir and pumice (or Turface, or crushed granite, depending on what I have most easily available).

1 Part Coconut Coir

1 Part Pumice

I wouldn’t use coir indoors, as I discovered it didn’t dry out fast enough for most of my bonsais. However, it’s great for outdoors in warm, dry climates.

The added pumice, which is also lightweight, allows the soil to drain a little faster without drying out too quickly.

What about the bagged boxed mixes at hardware stores?

If you aren’t able to find any of the soil components listed in the recipes above, the next best solution is to pick up a bag of “bonsai and miniture tree mix” at your local Bunnings, Home Hardware or Mitre 10 store.

This soil works fairly well for bonsais. However, it doesn’t drain very well, and it tends to repel water when it’s completely dry. I highly recommend adding in a rock material such as pumice, crushed granite or even perlite.

Do I need to repot my bonsai trees right now?

If your bonsais are currently doing well in the soil they’re in, don’t repot just yet. As I said in the beginning, the right soil for your bonsai tree depends on your climate, as well as the location in which you keep your plants.

In other words, if it’s working… stick with it.

On the other hand, if you’ve found that your bonsais are frequently dying, and you can’t quite figure out what’s going wrong, the soil is a great place to start.

While replacing your soil mix may not solve all your problems, your bonsais will be much happier in a soil that drains well and has plenty of airflow around the roots.

Repot new bonsai trees in new bonsai soil

As soon as you bring home a new bonsai, repot it in new soil as soon as possible, removing most of the soil from the store pot. Many common problems with bonsais come from keeping bonsais in their original store/plant nursery-bought soil.

Soil from the store poses two main problems. First, bonsai trees purchased locally tend to be root bound (meaning the roots are filling up most of the pot). If you simply remove the bonsai and place it in a new pot, the roots will have a hard time spreading.

Second, most nurseries sell bonsai trees in soil that is not designed for long-term growth. Or at least not long-term anywhere other than a greenhouse.

This is because large nurseries and growers generally use the same soil for all their plants. They want a soil mix that will work for almost anything. When bonsai trees are small, they need more water, so dense soil (like regular potting soil) works at that stage.

But leaving bonsais in this soil for too long can quickly cause a bonsai to rot–or in some cases, prevent it from getting the water it needs.

Peat moss is the primary ingredient in most potting soils. When the moss dries out completely, it tends to repel water.

If you don’t let the water soak on top of the soil and start to penetrate the peat, the bonsai won’t get any water. The water simply runs down the sides of the pot and out the bottom.

So please, for the health of your bonsai, replant them as soon as you can after purchasing. They will greatly appreciate the healthy new soil and room for their roots to spread.

Conclusion

The soil you use for your bonsai is just as important as the frequency of your watering.

Take a moment to examine the soil you’re using for your bonsai tree, and see if you a change might be in order.