Bonsai Organic Fertilizer: Pros, Cons, and How-Tos


Organic fertilizers have several advantages for bonsai cultivation, such as the slow release of nutrients, the improvement of soil’s ability to store and supply nutrients, and the improvement of soil structure.  However, there are also some drawbacks to consider, such as inconsistent nutrient content, risk of soil compaction, potential attraction of pests, and the possibility of containing harmful elements.

What organic fertilizer to use for bonsai?

Organic fertilizers are ones that are naturally produced or produced in a natural way.  There are different types of organic fertilizer that can be used to grow bonsai trees, each with its own unique nutrient balance.

Some of the commonly used organic fertilizers in bonsai growing include compost, animal manure, bone meal, and bonsai oil cake.


Espoma Organic Land and Sea Gourmet Compost

(Link to Amazon)

Compost is a type of organic fertilizer that is created when organic matter breaks down, such as leaves and dead insects, over time.  It improves soil condition, aeration, water-holding capacity, and contains a wide range of plant nutrients.

When incorporated into the soil mix, compost can give bonsai trees a baseline of energy they need even when growers failed to feed them enough.

Animal manure

Animal manure, such as chicken or cow manure, is a type of organic fertilizer that provides a good source of essential nutrients, such as nitrogen and phosphorus.  Composted chicken manure is rich in phosphorus with adequate nitrogen and provides a source of nutrients for flowering and fruit bonsai trees.

  • NPK ratio (chicken manure): 2:5:3
Bone meal

A bone meal is a type of organic fertilizer made from animal bones, usually in powdery form.  It is phosphorous-rich and beneficial when you use it for flowering and fruit bonsai trees.

  • NPK ratio: 4:16:0
Oil Cake

Oil cake (link to the online store at Bonsai Boy) is a byproduct of oil extraction from oil seeds such as cottonseed, canola seed, and soybean.  Once made into fertilizer through fermentation, bonsai oil cake fertilizer is optimal for leaf growth as it is high in nitrogen.  It releases nutrients slowly as well, providing a steady supply of nutrients for the bonsai tree.

  • NPK ratio (canola): 4:2:1

Why use organic fertilizers for bonsai?

Pros of organic fertilizer for bonsai

Bonsai trees, like all plants, require nutrients to grow and thrive.  While chemical fertilizers can provide these nutrients, many bonsai enthusiasts prefer to use organic fertilizers instead and you may be one of them.

Organic fertilizers offer several benefits that make them a great choice for bonsai cultivation including their abilities to:

  • provide nutrients slowly;
  • improve the soil’s capacity to store/supply nutrients, and
  • improve soil structure.

Provide nutrients slowly

Organic fertilizers release nutrients slowly due to their complex molecular structure, which takes time to break down.  It has the added benefit of reducing the number of fertilizer applications during the growing season.

Selecting a slow-release fertilizer is crucial when choosing bonsai fertilizer and organic fertilizers can provide them with this.

Improve soil’s capacity to store/supply nutrients

The organic fertilizer molecules that form from decaying organic matter are a substance called colloids.  These colloids can retain and provide a large number of nutrients like calcium, magnesium and potassium to plants as needed.

While clays also have a similar ability, the capacity to store and supply nutrients of organic fertilizers like humus colloids is much greater than that of clays.

Improve soil structure

One of the biggest benefits of using organic fertilizers for bonsai trees is improved soil health.  When organic matter decomposes, its molecules bind together particles of sand, silt, clay, and organic matter into aggregates that do not break apart when watered.

Soil health is an important component of bonsai cultivation.  A healthy soil structure provides the right conditions for the roots to absorb water and nutrients, and it also helps to anchor the tree and provide stability.

Cons of organic fertilizers for bonsai

While organic fertilizers offer many benefits for bonsai trees, there are also some drawbacks that should be considered.  Here are a few:

  • inconsistent nutrient content
  • risk of soil compaction
  • may attract pests
  • may contain harmful elements

Inconsistent nutrient content

One of the drawbacks of using organic fertilizers is that they can be inconsistent in nutrient content.  Two batches of compost or two different types of organic fertilizers can have different levels of nutrients because all natural beings are unique.

This can make it difficult to know how much fertilizer to use and how often to apply it to bonsai trees.

Soil compaction

Organic matter has the ability to bind together soil particles and makes aggregates that do not break apart when watered.  This is basically a good thing but too much organic matter mixed in the soil can make it too compacted for bonsai trees.

This is problematic because water drainage ability is one of the key features that bonsai soil should have.

May attract pests

Organic fertilizers can attract pests such as worms and insects if they are not aged and composted enough.  This may not cause any harm to bonsai trees but for some, it may be disturbing when worms creep around the bonsai soil.

May contain harmful elements

Organic fertilizers can contain harmful elements such as pathogens that can harm your bonsai trees.  This tends to happen when you make your own organic fertilizers at home but can happen when you buy from an unreliable shop.

It’s important to weigh the benefits and drawbacks of using organic fertilizers for bonsai trees when making a decision on what type of fertilizer to use.

Organic vs. inorganic fertilzier for bonsai

Organic fertilizers provide a diverse range of nutrients to bonsai trees.  The release of these nutrients into the soil is slow, which reduces the risk of over-fertilization and allows trees to absorb nutrients more effectively.  They can also improve soil’s ability to store and supply nutrients, besides providing nutrients themselves.

In contrast, chemical fertilizers contain specific, highly concentrated nutrients.  Although they give a quicker result, the rapid release of these nutrients into the soil can lead to over-fertilization.  Also, the nutrients can be washed out of the pot with frequent watering and not be fully used by bonsai trees.

The table below shows some of the differences between organic and inorganic fertilizers.

Characteristic Organic Fertilizer Inorganic Fertilizer
Origin Natural Man-made
Nutrient Content Diverse Specific
Nutrient Release Rate Slow Fast
Soil Impact Improves soil Can degrade soil
Water Solubility Low High
Availability of Essential Nutrients Limited High
Cost High Low

It is important to note that both organic and inorganic fertilizers have their benefits and drawbacks, and the choice between them will depend on what your bonsai trees need and your priorities.

For bonsai trees, choosing slow-release fertilizer is crucial because they have less nutrient loss and a lower risk of overfertilization.  Organic fertilizers are usually slow-release but there are inorganic fertilizers that are slow-release.

As to your preferences, you may want organic fertilizers for their natural origin and positive impact on soil health.

How to homemade bonsai fertilizer: a step-by-step guide

What is bonsai oil cake fertilizer?

Oil cake is a type of organic fertilizer made from the remains of oil seeds after oil extraction. Traditional bonsai fertilizer (“Tama-hi”: ball fertilizer) is made from oil cake and many growers used to make their own bonsai fertilizer at home until a few decades ago.

Its manufacturing process is the same as that of “bokashi” fertilizer: another traditional Japanese organic fertilizer made through the fermentation process.

Although regular compost and bonsai oil cake fertilizer/ bokashi are both organic fertilizers, bonsai oil cake fertilizer/ bokashi is different from usual compost in the sense that the input matter is fermented, not decomposed.

Fermentation process

The fermentation process of bonsai oil cake fertilizer can be both aerobic and anaerobic.

Aerobic fermentation requires the presence of oxygen because this process involves aerobic microorganisms such as acetic acid bacteria (which make vinegar) to convert organic matter into organic fertilizer.

On the other hand, anaerobic fermentation occurs in the absence of oxygen.  This process involves anaerobic bacteria such as lactic acid bacteria (which make yogurt) to break down organic matter.

The aerobic fermentation process takes less time while the anaerobic fermentation process requires less care after mixing the ingredients.  Some differences aside, the nutrients that they provide are almost the same whether they are made through aerobic or anaerobic fermentation.

How to make bonsai oil cake fertilizer: a step-by-step guide


To make bonsai oil cake fertilizer, here is what you need.

  1. Oil cake- canola or soybean extracts
  2. Bone meal
  3. Bokashi accelerator (optional)
  4. Water
  5. Scoop
  6. Sheet or container to mix
  7. Pan (aerobic fermentation)/ airtight container (anaerobic fermentation)
Oil cake

Theoretically, you can make bonsai fertilizer from any leftovers like meat, vegetable, or coffee grinds.  But different food has different nutrition elements which may or may not be good for bonsai trees.  So be careful when you choose what to use for making your own fertilizer.

I think it is safer to use canola seed or soybean extracts because they are used as ingredients for bonsai fertilizer for a long time and we know they are beneficial for bonsai trees.  Their NPK ratio is;

  • Canola- 4:2:1
  • Soybean- 7:1:1
Bone meal

Bone meal is to boost phosphorous to the fertilizer.

Bokashi accelerator

Fermentation can occur naturally by just mixing the ingredients but it is much easier if you add specific microorganisms that promote the process.

Bokashi accelerator as a product is a mixture of microorganisms, bran and sugar that promotes the fermentation process.  There are a couple of products available on Amazon (e.g. All Seasons Bokashi Compost Starter

All Seasons Bokashi Compost Starter

This product is for anaerobic fermentation).

For aerobic fermentation, I couldn’t find any commercially available products.  Acetic acid bacteria, which make vinegar, are aerobic bacteria that are found on the surface of fruit of traditionally fermented food such as wine and apple vinegar.  So, you may be able to add grape or apple skin for this purpose.

How to make

Once you got all the ingredients you need, you can start making your own bonsai oil cake fertilizer at home.  Here’s a step-by-step guide for you.

Step 1: Mix the ingredients

Put oil cake, bone meal (and bokashi accelerator) in a container or spread them on a sheet.  The ratio of the mixture is 8 for oil cake and 2 for bone meal.  To add commercially available bokashi accelerator, read the instruction and add the necessary amount (can be 10-20% of the total weight of ingredients).

Mix them well.

Step 2: Moisten the ingredients

Moisten the ingredients.  For aerobic fermentation, the volume of water is 30% to 40% of the weight of the total ingredients.  For anaerobic fermentation, the volume of water is 10% to 20%.

In both cases, the mixture should be moist but not soaking wet, such that you are able to make the mix into balls but those can be broken down easily when you squeeze a little.

Step 3: Spread over a pat/ put in a container

For aerobic fermentation, spread the mix out on a pat or sheet about 2 inches (5 cm) in height.

For anaerobic fermentation, put the mix in an airtight container.  To promote anaerobic fermentation, remove as much air as possible before sealing.  Seal the container tightly and prevent it from coming into contact with air as much as possible.

Step 4: Aerate (for aerobic fermentation only)

For aerobic fermentation, you need to turn the mix so that oxygen is available for the mixture.  The best time to do this is when the internal temperature rises to around 120°F  (50°C), which is in around 3 days to a week.  You may need to repeat the process a few times before completion.

Step 5: Allow it to mature

Once triggered into action, microorganisms will take care of the fermentation process.

For aerobic fermentation, the whole process may take around 4 weeks to complete.  For anaerobic fermentation, it may take 20 days when the average ambient temperature is 85°F (30°C) (the process is complete when the cumulative average temperature reaches 1110 (600℃) or higher).

Step 5: Check the smell

Check how it smells.  When the fermentation is successful, it smells sweet and sour like sourdough.  If it smells putrid or is covered with mold, it is likely unsuccessful and you cannot use it as a fertilizer.  Using an unsuccessful fertilizer may have an adverse effect on your bonsai trees.

Step 6: Dry and store

After the process is done, make the mixture into balls with a diameter of 1 inch (3-4 cm) and dry them well under the sun with sufficient airflow.  Once completely dried, fermentation by microorganisms stops and storage becomes possible.

Store them in a bag or container.  It is recommended to use it up within 6 months as there is a risk of mold or a decrease in fertilizing effect.

You cannot keep the mixture as it is after the fermentation process is done, especially for anaerobic fermentation because it cannot be in contact with oxygen every time you open the container.  It may also go bad or be covered with mold.

How to use bonsai oil cake fertilizer

Once bonsai oil cake fertilizers are dried, you are ready to use them.

Bonsai oil cake fertilizer should be applied once a month to a month and a half in spring and fall.  Avoid fertilizing during hot summer and winter because bonsai trees are stressed or dormant.

Here is how to use the bonsai oil cake fertilizer you made at home.

  1. Place bonsai oil cake fertilizer towards the edge of the pot and away from the surface root.  The amount of fertilizer depends on the size of the pot; a pot with a diameter of about 12 inches (30cm) should have 4 to 5 pieces.  For smaller pots, divide one into the appropriate size and apply.
  2. Place the next fertilizer after the last ones are completely dissolved.  Apply them between the places where you placed them last time, instead of placing them in the same spots as last time.

How to make bonsai liquid oil cake fertilizer: a step-by-step guide

Bonsai oil cake fertilizer can be in a liquid form.  Here’s a step-by-step guide to making bonsai liquid oil cake at home.


To make bonsai oil cake liquid fertilizer, here is what you need.

  1. Oil cake- canola or soybean extracts: 1L
  2. Bone meal: 0.2L
  3. Water: 10L
  4. Container with a breathable lid

How to make

Here’s a step-by-step guide to making liquid oil cake fertilizer at home.

  1. Put 1L of oil cake, 0.2L of bone meal and 10L of water in a container with a breathable lid, mix and cover it with a lid.  The container can be a bucket if you can put a lid on it.
  2. Stir occasionally, 2 to 3 times a month.  It smells rather bad when it starts to ferment.
  3. When the bad smell disappears, it is a sign that the fermentation has progressed sufficiently.  The process is complete in 15 to 30 days in summer and 2-3 months in winter.  The longer the maturing period, the better.  Ideally, it should be matured for more than 6 months.

You can make this in summer but winter is better because no flies and insects are attracted in the colder season.

How to use bonsai liquid oil cake fertilizer

Here is how to use the bonsai liquid oil cake fertilizer you made at home.

  1. If the soil in the pot seems dry, water it well to give moisture to the soil before fertilizing.
  2. Dilute the upper portion of the liquid fertilizer you made 10 to 15 times with water before use.  Dilution to this extent would have little risk of overfertilizing.  That said, avoid applying it to the leaves as it may cause damage to the leaves.
  3. Apply the diluted solution over the soil.
  4. Leave enough time until the next irrigation as the nutrients will flow out with watering.

How to make a custom organic fertilizer blend

Bonsai trees come in a wide variety of species, each with its own unique fertilizer needs.  When creating a custom fertilizer blend for your bonsai tree, it is important to consider the tree’s species, age, and growing conditions.

Before we dive into this, you may want to know what kind of nutrition bonsai trees need.  I wrote a whole section in an article addressing this in this post on the site.  In short, they need a fertilizer with an NPK ratio of 2-1-1 or 4-2-1, emphasizing the nitrogen ratio for leaf growth.

Back to the custom fertilizer blend, here is a general guide to help you create one for each bonsai tree species.

Coniferous bonsai trees

Coniferous trees have lower nutrient requirements but overall, you should aim for a fertilizer blend that is high in nitrogen for leaf growth.

Choose organic fertilizers that are high in nitrogen, such as oil cake.

Their nutrient need also depends on their type as well.  Pine trees (pinus species) need lower N and P but higher K while spruce (picea species) need higher N and P but lower K.

Deciduous bonsai trees

Deciduous trees require higher nutrient amounts compared to coniferous trees as they have to produce a whole new canopy of leaves every year.  For leafy growth, nitrogen is important.  Oil cake and fish meal contain a higher level of nitrogen and are good for deciduous trees.

Flowering and fruit bonsai trees

Flowering and fruit trees require a fertilizer blend that is high in phosphorus and potassium when flowering and fruiting.  For this, chicken manure contains a higher amount of phosphorus as well as potassium.  Bone meal contains a very high amount of phosphorus.

The following table shows the nutrient needs of bonsai tree species and the organic matter that provides their necessity in higher amounts.

Nutrition need and organic matter you may add by species

Species Nutrient needs Organic matter
Coniferous High in nitrogen, low in phosphorus Oil cake
Deciduous High in nitrogen and phosphorus, with a smaller amount of potassium Oil cake, fish meal
Flowering/Fruit High in potassium and phosphorous Bone meal, chicken manure

It is important to keep in mind that bonsai trees may have different fertilizer needs at different stages of their life cycle.  Young bonsai trees require more fertilizer than mature trees, while trees that are recovering from stress require a reduced amount (or none) of fertilizer.

To detect nutrition surplus and deficiencies and how to fix them, this post might be helpful. 

By paying attention to your bonsai tree’s specific fertilizer needs and adjusting your fertilizer blend as needed, you can help ensure that your tree receives the right balance of nutrients for optimal growth and health.

Copied title and URL