Like any plant, bonsai need soil to anchor the roots and provide plants with nutrients. But bonsai soil is a little different from potting soil and garden soil.
Bonsai trees have specialized needs, and the soil you use should reflect these needs. Many of these requirements are based on the fact that bonsai are often grown in small pots without much room for a root system.
Bonsai soil is arguably the most important component of bonsai, aside from the plant itself. Good quality bonsai soil provides the roots of a bonsai with an anchor, proper drainage, and vital nutrients.
In this post, we’ll discuss how to choose a good soil for your bonsai, and what to watch out for when it comes to purchasing bonsai soil.
Is Bonsai Soil Really “Soil”?
Bonsai soil is not really “soil” in the way most people think about it. Most of us are used to planting our trees and shrubs in soil that is made up of large amounts of organic matter such as peat moss, humus, and compost.
Bonsai soil is drastically different than this.
It is an inorganic blend that has been specially formulated to promote aeration while still retaining just enough moisture for your tree.
It consists of some combination of gravel, sand, clay, and/or volcanic rock.
Why Is Bonsai Soil Different?
Garden soil is used for growing plants in the ground and holding them in place. The soil needs to retain water, provide nutrients and provide support for a plant’s roots.
To accomplish this task, garden soils are usually a mix of sand (for drainage), silt (retains water), and clay (provides support).
Bonsai soils are designed with drainage as their primary goal. In nature, trees will usually have extensive root systems that are constantly seeking water.
Bonsai pots typically have only a small amount of growing area so it’s important that the tree roots can’t get too much water or they will rot. That’s why we use soils with large particles like pumice or lava rock.
These particles allow water to drain through quickly but don’t hold onto any moisture which makes them perfect for bonsai trees.
Bonsai Soil Aeration
Aeration refers to how much air is present in the soil. Having a good amount of air gives the roots room to breathe and promotes healthy growth. Less aeration leads to stagnant conditions that can cause disease, root rot, and other problems.
Good bonsai soil should have good aeration so that oxygen can move through the roots of your tree. You can do this by using aggregate material such as gravel or expanded clay pellets.
These materials allow for spaces between the particles allowing for airflow through the root system, but also allow water to flow around them.
If you use an aggregate, make sure it is not too coarse or water will flow through it too quickly, and take nutrients and fertilizer with it before they can be absorbed by the roots.
Bonsai Soil Drainage
The roots of a bonsai tree grow in a small pot with limited soil volume. If that soil holds too much water, the roots suffocate and rot, eventually killing the tree.
Properly mixed bonsai soil should drain quickly and hold just enough moisture to support healthy roots.
There are several ways to achieve this. For example, you can use bark or other organic matter that breaks down in the water, leaving behind an airy mix that drains well but retains nutrients.
You can also use pine needles or other types of mulch to improve drainage and keep the roots cool during hot weather. Or you can use clay or volcanic rock in your potting soil to improve drainage while retaining moisture in the soil.
Just be sure not to use too much clay or volcanic rock, as they can make it difficult for plants to absorb nutrients from the soil.
Bonsai Soil Water Retention
A good bonsai potting mix should hold some water so your tree doesn’t dry out between watering sessions. If it drains too quickly, the roots will dry out and the tree may die.
Retention of nutrients:
It must hold nutrients that are essential for the health of the tree and its proper development.
Organic vs. Inorganic Bonsai Soil
Inorganic Soil
Inorganic soil has become increasingly more popular as bonsai enthusiasts have realized that inorganic soils allow for better drainage than organic soils.
In addition to providing excellent drainage, inorganic soils also hold nutrients longer than organic soils do. This is extremely important because bonsai trees require frequent feedings.
An inorganic soil will say longer usually break down over time and need fewer replacements over years.
The downside to using inorganic soil is that it’s not as effective at retaining moisture as organic soil is.
This means that you will need to water your tree frequently if you choose an inorganic soil mixture. Fewer waterings will likely result in a dead tree!
Inorganic soil is made up of ingredients such as pumice, lava rock, and akadama. Each ingredient offers different benefits.
Pumice:
Pumice has an amazing ability to retain water while allowing air to pass through. It also provides a great amount of drainage, even when it’s wet! Pumice is a great addition to any soil mix and offers many benefits for your tree’s health!
Lava Rock:
Lava rock has similar properties as pumice but provides slightly less drainage and water retention. The unique thing about lava rock is that it does not decompose as other organics can over time, which means you won’t have to repot as often as with other growing mediums.
Akadama:
Akadama is a clay-based soil that is the most common bonsai soil in Japan. Akadama is only found in Japan and has a very distinct reddish color when it is wet.
It holds water well and is considered the best soil for performance over time.
The key downside to akadama is it breaks down quickly, so it must be changed annually or even semi-annually depending on the climate conditions.
Akadama contains minerals that are vital for the health of your bonsai tree. It comes in different sizes, but they all have great drainage abilities.
Turface:
A good alternative to akadama that can be found locally is “turface” which is a calcined clay that has similar properties as akadama but is more affordable. It can be rehydrated if it dries out and becomes crumbly.
This will greatly increase the amount of air in the soil, which keeps the roots healthy. Turface is an organic material used on baseball fields as a way to dry out wet spots on the field.
Grit/Gravel:
Coarse gravel or small rocks are often used alone or mixed with other materials. They provide excellent drainage and aeration but don’t hold water very well.
This means they must be watered frequently (hopefully at least twice a day), but they also dry relatively quickly, reducing the chances of root rot. This can be good for trees that thrive in rocky soil, like juniper and certain varieties of pine.
Gravel and grit are typically used for drainage purposes only, and not for providing nutrients to the plant.
Diatomite
This is a tiny fossilized form of algae with minute pores on its surface that hold water like a sponge.
Organic Soil:
Organic soil is made up of composted material from plants and animals. Organic bonsai soil tends to retain moisture better than inorganic soil, but it also breaks down faster.
Organic soils are made from a variety of organic ingredients such as composted bark, composted pine bark fines, sphagnum peat, etc. These decompose over time and provide the tree with nutrients.
Never use soil that has been previously used as it may contain harmful insects or diseases.
Moss
The most widely recognized kind of natural material utilized in bonsai soils is peat moss. This substance is extremely light and spongy, which permits air pockets to shape inside the dirt.
Moss additionally assists tree roots with getting oxygen all the more effectively, which stops root rot and other sicknesses from happening.
Tree bark
Conifer bark (such as pine bark) comes in many different sizes and textures and is used by itself or in conjunction with other components such as peat moss or akadama.
It breaks down slowly over time and provides good aeration while having a high water-holding capacity. Conifer bark is available at most garden centers and online retailers.
Organic vs. Inorganic Soil: Which One Should I Choose
Organic matter tends to break down quite rapidly in an enclosed environment such as a container. This means that you would have to repot your trees more often than you might like.
Organic matter can also be a source of diseases and insects if your trees are not healthy or strong enough to fight off any problems that might arise.
Organic soil is great for beginners because it doesn’t require much maintenance or special attention. It’s also great for anyone who isn’t interested in composting and making their own soil.
Inorganic soil is perfect for anyone who wants to fine-tune every aspect of their bonsai experience, including the soil. It takes a bit more time, effort, and knowledge to use but will help make your trees the healthiest they can be.
How Can You Make Bonsai Soil at Home?
When choosing a type of soil to use in your bonsai containers some factors come into play. The following is a list of questions to ask yourself when choosing a bonsai soil:
Is this for an indoor or outdoor tree? Does this tree prefer acidic or alkaline soils? What kind of textures do I want my soil to have? Is this tree fast or slow-growing?
Once you got answers to those questions it is fairly simple to make your own bonsai soil at home.
Mixing Ratios:
For making bonsai soil at home, you will need a mix of different ingredients. The ratio of the put-together ingredients depends on the type of tree and season you are planning to bonsai.
In general, though, you will want a mix of 50% inorganic material (such as clay or gravel) and 50% organic material (such as bark or moss).
The inorganic material provides water retention and nutrients for your plants, while the organic material provides drainage and aeration.
Common Mistakes When Growing Bonsai
Here are some common mistakes people make while preparing bonsai soil at home:
Using Too Many Water-Retentive Materials
Even though it is important to ensure that the soil retains enough water, this does not mean that you should use a lot of water-retentive materials.
Bonsai soil must drain well and should be porous enough to allow oxygen to pass through the roots. If the water is held in the soil, it will suffocate your tree’s roots and eventually kill your Bonsai.
if your potting mix contains too many water-retaining materials, it can cause problems for the tree. Make sure you use a good mix of both water-retentive and aerating materials.
Using Too Much Water Draining Materials
In some cases, people use too many water-draining ingredients such as gravel or pumice which results in the soil drying out too quickly.
This can be very detrimental to the health of your tree, especially if you are not diligent about watering.
Water-draining materials are essential to the health of the plant but not in excess.
It is always better to err on the side of caution, using less water-draining materials until you get a feel for how often you need to water your tree.
Using Wrong Soils
Not every bonsai tree will thrive on the same bonsai soil. Each plant requires its own particular mix of nutrients and minerals, and you have to make necessary adjustments as per your tree’s preference.
Make sure you are using the correct soil type for your bonsai tree. A tree growing in a faulty soil environment will never flourish.
Not Giving Enough Food
Bonsai trees require a lot of nutrients to grow properly and look great. They are usually planted in small pots and their roots are often cut short, so they cannot absorb as many nutrients from the soil as normal plants do.
Because of this, it is essential to feed your bonsai with fertilizers regularly in order to maintain their health and vitality.
One of the most common mistakes is not providing enough fertilizer which can cause stunted growth or even death of the plant in some cases.
Not Enough Aeration
The soil needs to be aerated constantly if you want to keep your tree healthy.
Many bonsai trees are planted in pots with drainage holes. While these are necessary for getting rid of excess water, they aren’t enough to let air into the soil.
Many gardeners also plant their bonsai in soil that is too wet or too tight together. These two factors combined can lead to root rot and other problems that can harm your tree.
Make sure that you check the condition of the roots regularly, and repot if necessary to prevent these problems from occurring.
Conclusion
Bonsai soil is arguably the most important component of bonsai. The soil you choose for your bonsai will have a significant impact on its overall health.
It is not something that you can choose by price alone. There are other important factors to consider. To ensure that you are giving your bonsai the best possible chance at surviving and thriving, make sure to pick an appropriate soil that is right for your plant.
Bonsai soil provides the air, water, and nutrients that feed your tree. To ensure the tree receives these essentials, it is important to know how bonsai soil works and what to look for when choosing a planting medium.
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