Soil For Bonsai
Here we go again with the commonly debated subjects of Bonsai Soils, This time though I’m looking to answer some specific questions that relate to the subject and see if we can have them make more sense. We have to remember that there are different goals for different growth stages of trees and there are also different environmental factors to take into account.
Here’s the Questions we will cover
- Can I plant bonsai in regular potting soil?
- Do I need special soil to repot bonsai?
- How do I make my own bonsai soil?
- What bonsai soil mix to use without akadama?
These are some of the more common questions about bonsai soil I get in my nursery and through emails online so lets take a look at answering them.
Can I plant bonsai in regular potting soil?
Regular potting soil is good for bonsai plants that are in the development stage as it helps retain moisture, nutrients and heat. This will help grow a strong root system and grow your tree quicker. It is still a good idea to break that up with something like perlite or pumice though to make sure it drains well. There are a few issues that organic soils cause for trees in the refinement stage of bonsai that aren’t a cause for concern in development. This is because both the pot and goals of the tree change. Organic soil is dense and very nutrient rich, in development this is fine because we are looking for strong growth so having an abundance of nutrients isn’t a bad thing, with the soil being dense this is also good as it holds heat which is a requirement for strong root growth and there is less oxygen which causes thicker root growth which = thicker top growth. But it’s the growing pot that allows you to utilize the dense organic matter because it is taller, this height allows for a greater gravity column which helps drain the dense potting mix. If we look at a tree in a bonsai pot ( refinement ) we can see that we now have a very shallow pot with minimal gravity column, so this make it harder for soils to drain. This is where we need to change over to something that is a lot more free draining and introduces more oxygen into the mix which also helps grow smaller roots in combination with other things. We can also see that in refinement we want smaller leaves and smaller branches so we now want a smaller more controlled amount of fertilizer.
So in summary yes you can use regular potting mix with your bonsai if they are in the development or growing phase in a growing container. If your tree is in a bonsai pot and in refinement you will want to steer clear of it as it can cause issues.
Do I need special soil to repot bonsai?
Its not that you need special soil to repot your bonsai with but there are substrates that will be more beneficial. When repotting bonsai its good to use things like Akadama, Pumice and Lava Rock as they add more drainage and better nutrient control. This can reduce the chances of things like root rot and excessive growth on your tree which can ruin your design.
Like we spoke about above when moving your tree into the bonsai pot lots of things change so your soil should change as well to suit your new goals and the limitations of your trees new home ( the bonsai pot ). If you can do this you will have the best chance of achieving good health for your tree and great material to be able to design with.
So in short what are the substrates?
Akadama : This is a clay mined from Japan that has good moisture retention, a small amount of nutrient retention and it breaks down as the roots grow into it effectively splitting the roots making them finer.
Pumice : This is a volcanic substrate that has lots of pores that hold both moisture and oxygen, pumice can be used to increase moisture retention slightly in a mix or oxygen depending on the ratios that you use it with the other substrate. Pumice doesn’t break down so it is used in trees that require a longer repotting cycle to prevent total break down of the mix. Pumice does have a Cation Exchange Capacity but it is too low to take into account for nutrient retention in your mixs.
Lava rock : This can also be called Kiryu or Scoria. This is a substrate that introduces oxygen to the mix and helps prevent the break down of a mix over time. This substrate has even less ability then pumice to hold nutrients.
How do I make my own bonsai soil?
To make your own bonsai soil you need to acquire the substrates or organic materials that are available to you. Before you acquire them though you need to take into account all your environmental factors and species requirements. This will change what you use and what ratios you use. To learn this we have a full section in our online bonsai beginners course that covers what to consider.
Once you have your components you will want to make sure you sieve the particles to separate them into their proper sizing and also give them a good sieve to remove as much dust and fine materials as possible as this can clog up your drainage. Once you have done this you can mix them at the ratio you came up with depending on your species and environment.
What bonsai soil mix to use without akadama?
In the case where you don’t have access to akadama I would advise substituting it with pine bark nuggets. It wont be perfect and you will miss out on the advantages of akadama but at least you will add some good moisture retention and nutrient retention back in the mix. I would still use pumice and lava rock to keep the mix nice and open. In the case where you cant afford or cant gain access to any of the substrates talked about in this article you can revert back to potting mix but I would be mixing it heavily with perlite to open it right up as much as possible, and minimise the amount of nutrient retention to try and keep some control over the tree.
I hope this article has answered a few more questions about bonsai soil for you and has helped get you on the right path for success.