The soil you plant your Bonsai into has a direct effect on the health and longevity of your Bonsai tree. Each Bonsai has a preference for its own soil mix, so making sure you have the right Bonsai soil mix is essential.
Bonsai soil is not actually soil in itself, as it contains a mix of materials rather than soil. Some refer to this as a “growing medium” or a “substrate” but we will call it “soil” for simplicity.
The aim of any Bonsai soil is to provide three key functions for your Bonsai:
- Water Retention
- Drainage
- Aeration
Why is drainage important for my Bonsai Soil?
Why is drainage important for my Bonsai Soil? Without the correct drainage your Bonsai will become waterlogged and can cause issues such as “root rot” which will greatly affect the health of your Bonsai.
In order to find what type of soil your tree likes best, you have to try out some different soil mixtures. You can start with a basic soil mix and then keep track of your tree and soil health to know when to adjust your mix. This way you can make sure you have the best drainage, aeration and water retention for your Bonsai tree/pot/position combination.
It’s a good idea to have a notebook handy to write down the different soil mixtures you try so that, when you hit upon the best one, you can reproduce it without having to go through the trial and error again.
How to make Bonsai soil
To get started, there are two basic types of Bonsai trees and they respond better each to a different mix of Bonsai soil. These are the coniferous and the deciduous Bonsai varieties:
Soil Mixes For Deciduous Bonsai Trees
A deciduous Bonsai tree is one that sheds its leaves in the Fall (Autum) months to go into its dormant period over Winter. Popular types of deciduous Bonsai include Maple, Elm and Wisteria varieties.
The best soil mix for deciduous Bonsai trees will contain more clay based substrate (such as Akadama) to aid in water retention. A great mix to start with is 2 parts Akadama, 1 part pumice and 1 part Lava rock.
As deciduous trees drop their leaves for the dormant period in nature they will actually provide their own organic compost (the decaying leaves) for their re-growth. With a Bonsai though this will not happen as effectively, so remember that your tree may require some addition help in the way of a good fertiliser going into its growing period.
Soil Mixes For Coniferous Trees
A coniferous tree has needle-shaped or scalelike leaves and will be an evergreen variety, meaning they keep their leaves in their dormant period. Common species of coniferous Bonsai tree are varieties such as cedar, pine or juniper.
The soil mix for a coniferous Bonsai tree should contain equal parts Akadama, pumice and lava rock.
Without your tree dropping its leaves for the dormant period it will be a little bit harder to notice when it goes into its growth period. This being the case make sure you keep an eye on it to know when to add a bit of fertiliser to help it along in the growth period.
Adjustments To The Soil Mixture
If your Bonsai soil mix is getting dry too quickly, increase the percentage of Akadama and decrease other types. Good water drainage is very important for your tree.
If you see that the water does not drain as it should, all more sandy soil. Soils like haydite will provide better drainage.
You should keep track of the health of your Bonsai tree and make adjustments to the soil mix as needed. The type of tree, pot it is in and position in your garden will all affect the ideal soil mix. It may take a little time to get the perfect mix but the rewards are worth it.
Can I use potting mix for my Bonsai?
It is not recommended that you use regular/normal potting mix for your Bonsai tree, as it does not provide the amount of drainage and aeration that a Bonsai needs. It is also a little too good at water retention, meaning you run the risk of your Bonsai developing “root rot” and seriously affecting its health. Your Bonsai may survive in potting soil but it will not thrive and grow into its full beauty.
Components of a Bonsai Soil Mix
Components of Bonsai soil will generally fall into two categories, organic and inorganic. There are many more components you can use, but for ease of understanding we will cover some of the most common types.
Organic
Organic material for your Bonsai soil is the material that will break down over time. You need to replace this often as, when the material beaks down, it increases the water retention. This will make your soil can become water logged and way too moist for too long.
Common types of organic materials used for Bonsai soil include:
- Bark – most often pine or conifer bark is used. This will add bulk to your mix and is also good for water retention
- Peat Moss – this is very often used in commercial potting mixes and should be used in only small amounts. Peat moss will retain a lot of water so should not make up the bulk of your mix
- Leaf litter – You can use this can be used to replicate the leaf drop of deciduous trees in nature. It is a great additive in your soil that will break down over time and provide nutrients to your Bonsai.
Inorganic
Inorganic soil types are less nutrient rich than organic types, but provide great aeration and drainage. Use these in greater portions that organic types when developing your soil mix.
Some of the most common types of inorganic material to use are:
- Akadama – this is perhaps the most common type of inorganic material used for Bonsai soil. It is a hard baked Japanese clay that is specifically created for Bonsai. Akadama is great for water retention but will break down over time. It does need to be replaced every so often.
- Lava Rock – is a very hard component that is also very porous and rough to the touch. Lava rock does not break down very easily and it great to provide aeration and drainage for your soil
- Pumice – a softer volcanic rock that is great to use in Bonsai soil. This retains water and nutrients and will also aid root growth. It allows the roots to ramify (where roots split into smaller limbs)
Can I mix organic and inorganic matter for my Bonsai soil mix?
The short answer is, yes you can. This being said, don’t mix in too much organic matter. While it is good that it breaks down and creates a type food/compost for your tree, it will retain water. This can lead to problems if you have too much water retention.
Bonsai Soil Additives
There are lots of different materials that you can add to their Bonsai soil to help its condition. You can add different things to your to feed the tree and help it look good. Although these aren’t absolutely necessary for growth, they’ll be beneficial in small amounts to the health of your Bonsai.
Some common types of Bonsai soil additives are:
- Lime – not generally recommended for Bonsai, but sometimes added the lower the acidity of the soil.
- Charcoal – helps to create a “filter” to help remove impurities in the water you are using
- Fertiliser – you can add either liquid or soil fertiliser to help “feed” your tree. This is most commonly added just before the growing season
- Peat Moss – extra water retention, but use sparingly
- Bone Meal – a slower release type of fertiliser
Why do people put moss on top of their Bonsai soil?
Firstly, because it looks great! Adding moss to you Bonsai will definitely make it look the part, but there is another benefit it provides. Much like adding mulch to the top of your vegetable patch, moss on top of your Bonsai soil will help the soil to retain moisture by limiting evaporation. This will mean your soil will stay moist (not wet) for a longer period.
Tools You Will Need To Change Bonsai Soil
As part of your Bonsai maintenance, it is important that you have a Bonsai tool kit. This will include tools used in changing the soil for your Bonsai.
The basic tools that you should have to change your Bonsai soil include:
- Root hook – this will help to untangle your root ball and make it easier to cut back
- Root cutter – this can be a simple as a pair of scissors or even a set of pruners. This will allow you to cleanly cut back the roots of your Bonsai
- Soil scoop – to move the soil into your Bonsai pot cleanly. A small spade will do the tick.
- Watering can – to water in your Bonsai once you have changed the soil.
These tools will make up an integral part of your Bonsai tool kit. Remember to always keep them clean and sharp, this will make sure they always function properly. Bonsai tools can be expensive, so it’s important to make sure they are kept in good condition so they last a long time.
Where to buy Bonsai soil mix or components?
The best place to buy your Bonsai soil mix supplies is from your local Bonsai nursery. A Bonsai nursery will have all of the components your need to mix your own soil, and also a lot of pre-mixed Bonsai soil you can buy.
A Bonsai nursery will have different mixes available for different types of trees, so you wont have to mix them yourself. They also have great staff there who are into Bonsai as well, and have loads of knowledge on the types of soils. Asking questions of the staff is a great way to learn and get your Bonsai off to a good start.
Another option is to buy your Bonsai soil online through an online store (like Amazon). You will have to do your own research first to make sure you get the right one, but the online stores are a great option if you don’t live near a Bonsai nursery.
Bonsai soil we recommend
If you want to save a bit of time researching, here are a few different types of Bonsai soil that we use and recommend. They are all available from Amazon so you can save yourself some time looking around the stores for them: