Bonsai Fertilizer Basics

Typical fertilizer display at a local garden center

Where does one start when talking about fertilizers for bonsai? The one thing I do know is that there is no such thing as “bonsai fertilizer.” Fertilizers come in all sorts of varieties, you can see that when you walk into your local garden center. You have fertilizers for absolutely everything. I bet when you walk into the garden center and walk over to the fertilizer section, you will see 10 or more kinds of fertilizers. What kind do you buy? What do you look for? Do you buy inorganic or do you look for something organic? What are these three numbers on the front of the package mean?

At the end of this article I will compare three different fertilizers that people use on their bonsai collections.

Let’s break it down and answer some of these basic questions. Let’s start with what you should be looking for. When I am looking for a fertilizer for bonsai, I am looking for something that is balanced. Balanced just means that the Nitrogen (N), Phosphorus (P), and Potassium (K) content are all equal. You will see this listed on the package label as three numbers usually appearing as 10-10-10 or 12-4-8 or something similar. That is the NPK rating of the fertilizer. The higher the number the more concentrated that nutrient is. Nitrogen helps plant foliage to grow strong. Phosphorous helps roots and flowers grow and develop. Potassium (Potash) is important for overall plant health.

If you were to stop reading now, you could walk into the garden center, find a fertilizer for under $10, follow the directions on the package and your bonsai would be fertilized and it would grow. However, just as with anything, there is more.

The NPK tells us the concentration of the three main Macro Nutrients, but here is the more I mentioned above. Plants are complex organisms with many different types of cells that require different nutrients to maintain their functions and to keep the plant strong, just like us as humans. If we lack nutrients in our bodies we are able to live, but we won’t be as strong and healthy as we could be. The different types of nutrients that plants require are the main Macro Nutrients, NPK, the three Secondary Nutrients, the Micro Nutrients followed by Vitamins and Minerals.

Secondary Nutrients

A Secondary Nutrient product

I have already mentioned the three main Macro Nutrients (N=Nitrogen, P=Phosphorous, K=Potassium). The three Secondary Nutrients are Calcium, Magnesium, Sulfur. These are considered secondary because they are not needed in as big of a quantity as the main nutrients, but they are still needed for a healthy bonsai. However, when looking at the contents of different fertilizers you will not see them included in all fertilizers.

Calcium is essential for the development of strong cell walls and is also used in cellular signaling, a biological process critical to a plant’s health. Magnesium plays a big role in the photosynthesis process because it is a building block of Chlorophyll, which gives leaves their green color. Sulfur in plants helps form important enzymes and assists in the formation of plant proteins. 

Micro Nutrients

A Micro Nutrient product

Micro Nutrients are only required in small (micro) amounts but are still very valuable to the health of our bonsai. There are seven Micro Nutrients that we always see listed as important, but there are others. The seven important ones are Boron, Chloride, Copper, Iron, Manganese, Molybdenum and Zinc. As important as Micro Nutrients are, you still wont find them in most fertilizers.

Boron plays a role in cell wall formation along with moving sugars (energy) throughout the bonsai. Chloride plays a role in photosynthesis, internal water balance by allowing proper stomatal openings and the suppression of plant diseases. Copper is required in the process of photosynthesis, it is essential for plant respiration and assists in plant metabolism of carbohydrates and proteins. Iron is essential in the formation of chlorophyll and it helps carry oxygen throughout the bonsai. Manganese is a major contributor to photosynthesis and respiration. Also aids in root cell elongation and resistance to root pathogens. Molybdenum is used by plants to convert inorganic phosphorus into organic forms in the plant. It is also used to convert nitrate into nitrite (a toxic form of nitrogen) and then into ammonia before it is used to create amino acids within the plant. Last we have Zinc. Zinc activates enzymes that are needed for the creation of certain proteins. It is used to help form chlorophyll and some carbohydrates, conversion of starches to sugars and its presence in plant tissue helps the plant to withstand cold temperatures. Zinc is essential in the formation of auxin, which help with growth regulation and stem elongation. 

Inorganic vs. Organic

Inorganic Fertilizer

There are a couple of notable differences between organic fertilizers and inorganic fertilizers. Organic fertilizers contain only plant- or animal-based materials that are either a byproduct or the end result of naturally occurring processes, such as manures, leaves, and compost. On the other hand, inorganic fertilizers are manufactured artificially and contain minerals or synthetic chemicals.

With inorganic fertilizers, the nutrients are provided in a plant-ready form immediately. However, the concentration of nutrients in this form (usually liquid) increases the risk of “burning” the roots of the plant if provided in the wrong amounts as well as building up of toxic salts in the soil. The rapid release of nutrients may leach them deeply into the soil or completely out of the bonsai pot so the bonsai can’t access them. What happens when fertilizing with inorganic fertilizer is that we pour the fertilizer onto the soil and it runs through the soil and collects where the water collects (in pores of lava rock or pumice for example). The bonsai absorbs the nutrients now, but when we water again tomorrow we are washing away the fertilizer. When you fertilize with an inorganic fertilizer with a complete inorganic soil we want to fertilize every 7-10 days to replenish the nutrients.

Organic Fertilizer Cake. Sumo Cakes

Organic fertilizers release nutrients when the soil is warm and moist (when we water our bonsai or when it rains), which tends to correspond with your plants’ times of greatest need. Organic fertilizers rely on soil organisms (mycorrhizae) to break down organic matter into a form that the plant can utilize, so nutrients are released more slowly than they are from inorganic fertilizers. This slow-release reduces the risk of nutrient leaching, but it takes time to supply nutrients to plants. What happens when you use organic fertilizers, whether in cake form (Sumo Cakes) or loose in tea bags. You place them on top of the soil and when you water your bonsai or it rains the fertilizer gets wet and the nutrients leach into the soil every time. You would want to replace the cakes or tea bags about every 4-6 weeks to maintain the nutrients going to the bonsai.



Mycorrhizae in the root system of a tree fertilized with Sumo Cakes

In the last paragraph, I introduced a term, Mycorrhizae. Mycorrhizae are helpful fungi and bacteria that colonize the root zone of plants and are very important in the overall health of our bonsai. Mycorrhizae help break down organic fertilizers into forms that the plant can absorb easily. Some mycorrhizae grow in the soil around the roots while others attach themselves to the roots. The mycorrhizae then are able to transport water and nutrients to the roots of the tree from places that the roots do not inhabit. In turn, by helping the tree grow strong, the tree returns the favor and transports nutrients to the mycorrhizae. Having a healthy colonization of fungal and bacterial growth in the bonsai pot creates a network in the soil that expands the area of the roots to greater absorb water and nutrients. At the same time as helping the tree absorb water and nutrients, the mycorrhizae help fight harmful fungal and bacterial attacks and can strengthen the overall health of the tree. 

Product Comparison

Organic Fertilizer

One thing you hear when it comes to fertilizers is that you can just go to your local garden center and pick up the cheapest fertilizer you can find and you will be OK. Now, this may be true, but take a look at Miracle-Gro liquid fertilizer simply called “Liquid All Purpose Plant Food”. It is an inorganic fertilizer that you can pick up for as little at $6 a jug. Its NPK rating is 12-4-8. It has the three main Macro Nutrients but it does not contain any of the Secondary Nutrients and it only has three Micro Nutrients. That is all that is guaranteed in the bottle. If you want to provide your bonsai with the rest of the nutrients, you are going to have to buy more products.

Let’s take a look at BioGold Original. It is an organic fertilizer caked into triangular pellets. It has an NPK rating of 5.5-6.5-3.5. Again it has the three main Macro Nutrients, but no Secondary Nutrients and only four of the Micro Nutrients. That is all that they guarantee. Again you may have to purchase other additives to provide the other nutrients. Sumo Cakes has a NPK rating of 4.8-4.8-4.8 and contains the three main Macro Nutrients along with the three Secondary and 7+ Micro Nutrients along with 70+ naturally occurring Vitamins and Minerals. Sumo Cakes also contains 39 different Mycorrhizae species. Sumo Cakes can be purchased at


In conclusion it is correct to say that any old fertilizer will do. However in the long run you might run into issues of different nutrient deficiencies. This could lead to the death of the bonsai, the loss of limbs, poor flower production, less budding and the list goes on. When you recognize the deficiency you do have the option of buying a product that contains the nutrient that you need to correct the issue.

When I created Sumo Cakes, I wanted to avoid the issues of different deficiencies and having to buy different products to fit the needs of my bonsai. I wanted a product that made feeding bonsai easy. I wanted a fertilizer that focused on the roots. I am happy to say that I now have one. I have always maintained that if you can’t grow roots, you can’t grow a bonsai.

This list consists of the fertilizer ingredients that are included in Sumo Cakes, but also serves as a good guide to what these individual ingredient can provide to any fertilizer mix.

Alfalfa Meal

Alfalfa is a good source of nitrogen, 16 amino acids and several other vitamins & minerals including:

  • Boron
  • Calcium
  • Iron
  • Magnesium
  • Phosphorus
  • Potassium
  • Sulfur
  • Zinc


  • Biotin
  • Carotene
  • Choline
  • Folic Acid
  • Niacin
  • Pantothenic Acid
  • Riboflavin
  • Thiamine
  • Vitamin A
  • Vitamin B
  • Vitamin E

The growth hormone “tricontanol”.

Ammonium nitrate

Ammonium nitrate is a popular fertilizer since it provides half of the N in the nitrate form and half in the ammonium form.
The nitrate form moves readily with soil water to the roots where it is immediately available for plant uptake. The ammonium
fraction is taken up by roots or gradually converted to nitrate by soil microorganisms.

Ammonium phosphate

Ammonium phosphate is an excellent source of P and nitrogen (N) for plant nutrition. It’s highly soluble and thus dissolves quickly in soil to release plant-available phosphate and ammonium.

Ammonium sulfate

The primary use of ammonium sulfate is as a fertilizer for alkaline soils. In the soil the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil, while contributing essential nitrogen for plant growth.

Bat Guano

  • Many necessary macro and micro nutrients.
  • Whole host of beneficial micro-organisms that cannot be duplicated by a chemical fertilizer.

Blood Meal


Bone meal

  • Phosphorus
  • Calcium

Calcium nitrate

Calcium nitrate is a fully water soluble nitrogen and calcium fertilizer. It is a fertilizer made up of two nutrients, with a white grainy appearance that dissolves quickly in water. It can be absorbed rapidly by plants.

Earthworm Castings

Worm Castings are packed with over 60 water-soluble vitamins & minerals that are essential for plant growth, and these minerals are immediately available to the plant, without the risk of ever burning the plant. Some of these nutrients include:

  • Nitrogen
  • Phosphorus
  • Potassium
  • Calcium
  • Magnesium
  • Borax
  • Carbon
  • Cobalt
  • Copper
  • Iron
  • Manganese
  • Zinc
  • The humic acid in Worm Castings stimulate plant growth. The humic acid is in a state in which it can easily be absorbed by the plant, over and above any normal mineral nutrients. Humic acid also stimulates the development of micro flora populations in the soil.
  • The humus in the castings extracts toxins and harmful fungi and bacteria from the soil. Castings therefore have the ability to fight off plant diseases.
  • Castings are also an effective way to repel white flies, aphids and spider mites and any pest that feeds on plant juices. According to recent studies, applying earthworm castings to the soil around your plants increases the production of a certain enzyme that is offensive to these insects.
  • Inhibits root diseases such as root rot.

Feather Meal

  • Nitrogen

Fish Bone Meal

  • An excellent source of organic phosphorous and calcium
  • High in trace elements
  • Includes beneficial soil microbes

Fish Meal

  • High in macronutrients
  • High in micronutrients
  • Contains all amino acids
  • High in vitamins, including the entire B-complex


  • Calcium

Hydrolyzed Fish

  • Amino acids
  • Growth hormones
  • Micronutrients

Kelp (Ascophyllum nodosum)

  • This species of kelp produces 70 different trace elements,  growth hormones, vitamins, enzymes, and proteins.
  • Provide resistance to disease and insects.
  • Kelp aids in building and or supporting the plants natural immune system

Kelp Meal

  • See Above
  • Kelp is a 100% natural source of over 70 vitamins and minerals.

Manganese sulfate

  • Manganese is one of nine essential nutrients that plants require for growth.

Magnesium nitrate

A good source of Magnesium and Nitrogen.

Norwegian kelp

Used by farmers for its rich value, seaweed feeds plants with a wide range of nutrients, growth bio-stimulants and conditioners.  Kelp Meal is a rich, natural, organic source of both macronutrients, Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S) and micronutrients (eg. Manganese (Mn), Copper (Cu), Iron (Fe), Zinc (Zn),). Ascophyllum Nodosum Norwegian Algamin Kelp Meal contains at least 60 Minerals or Elements, over 12 Vitamins and 21 Amino Acids (including the 17 considered vital) at a fraction of the price of mined minerals and synthetic vitamins.

Potassium nitrate

Potassium nitrate is a water-soluble Nitrogen and Potassium fertilizer.

Potassium phosphate

A source of phosphorus and potassium.

Potassium sulfate

Provides both potassium and sulfur.

Protein Hydrolysate

  • source of amino acids.

Rock Phosphate

  • Contains valuable trace minerals in addition to phosphorus

Sodium borate

Boron is an essential element for plant development, growth, crop yielding and seed development by helping the transfer of water and nutrition in plants.

It is essential in the balance between sugar and starch, and functions in the movement of sugar and carbohydrates.
• Valuable in pollination and seed production.
• Necessary for normal cell division, protein formation, and nitrogen metabolism.

Sodium molybdate

Sodium molybdate is useful as a source of molybdenum.

Sulfate of potash magnesia

  • A unique 3-in-1 combination of highly available sulfur, potassium and magnesium.


For plants that love acidic soils, urea is one of the top fertilizers for acidifying soils. For gardeners who grow crops like corn, strawberries, blueberries and other heavy nitrogen feeders, urea will supply immediate and powerful applications of nitrogen.

Zinc sulfate

  • Zinc

This is basic information on what role each Macro and Micro nutrient does for a plant. You don’t usually find all of the secondary macro nutrients or for that matter all of the micro nutrients in a single fertilizer. Most of the time we need to add these in to our fertilizing schedule. Buying and adding micro nutrients costs extra. With Sumo Cakes these are already in the cake. No need to add them.

Macro Nutrients

Macro Nutrients:

(N) Nitrogen

  • Nitrogen is considered the most important of the nutrients. That’s because without nitrogen, protein wont form, and protein makes up much of the tissues of most living things. Earth’s atmosphere consists of about 78 percent nitrogen by volume and all living things must have it to survive. Most plants can’t get their nitrogen directly from the air. Instead, nitrogen use follows an indirect path called the nitrogen cycle. Nitrogen in the soil isn’t always available to the plant as a nutrient. In fact, up to 98 percent of the nitrogen present in the soil is a component of decaying organic, or plant matter and is unavailable to plants in its existing form. Various soil bacteria do most of the work converting soil nitrogen to an inorganic form usable by plants. These busy microorganisms, mostly invisible without magnification, combine elemental nitrogen with hydrogen and oxygen in a process called mineralization that makes nitrogen accessible to plants.

(P) Phosphorus

  • Phosphorus is another one of the “big three” primary nutrients. Phosphorus is involved in many processes critical to plant development. The most important one among them is photosynthesis, the process that plants use when converting sunlight to energy. Phosphorus is also important to respiration, cell enlargement, cell division, energy storage and energy transfer. For all these reasons, phosphorus is integral to the quality of the plant and the fruit it produces.

(K) Potassium

  • Potassium is the third key nutrient in fertilizers. It helps strengthen the plants abilities to resist disease and plays a big role in increasing overall quality. Potassium also protects the plant when the weather is cold or dry, strengthening its root system and preventing wilt

Secondary Macro Nutrients:

Secondary Macro Nutrients:


  • Calcium helps roots and leaves grow strong and healthy. It helps strengthen overall plant structure, increasing resistance to wind, hail, insects, and other sources of physical damage.


  • Magnesium is the central atom in chlorophyll, the molecule responsible for photosynthesis, the process where plants turn sunlight and nutrients into green growth. Most of the magnesium in plants is found in chlorophyll. Like phosphorus, magnesium moves from the older parts of the plant to the younger as the plant grows.


  • Sulfur is essential for the production of amino acids, which are the building blocks of proteins found in all living things.

Micro Nutrients


  • Boron is essential for healthy cell growth in plants, and is important in the formation of pollen as well.


  • Chlorine helps plants manage water stress and may help some plants resist fungal diseases.


  •  In plants, copper is important mostly as a catalyst (it promotes chemical reactions without becoming part of the product of those reactions). Its indirect role is an important one, though: without it, plants will not develop normally.


  • Iron serves as a catalyst, especially in the formation of chlorophyll. It also helps regulate certain plant enzymes, and promotes root function in legumes. The leaves of plants deficient in iron often turn pale green or even yellow, a signal that the plant isn’t forming chlorophyll properly.


  • Manganese is yet another micronutrient that helps plants synthesize chlorophyll, as well as helping regulate several important plant enzymes.


  • Molybdenum helps plants make efficient use of nitrogen and phosphorus. That makes molybdenum important for plants; when there’s enough molybdenum available, the plants are better nourished by primary nutrients.


  •  Zinc helps plants form proteins, starches, and growth hormones,

Mycorrhizea is a word that means fungus root. These soil fungi create a network around the roots and in some plants in the roots. Over 90% of all plants benefit from mycorrhizea. Some of the benefits include the following:

  • Produce more vigorous and healthy plants
  • Increase plant establishment and survival at seeding or transplanting
  • Improve drought tolerance, allowing watering reduction
  • Enhance flowering and fruiting
  • Optimize fertilizers use, especially phosphorus
  • Reduce disease occurrence, including root rot



  • Gigaspora margarita
  • Glomus aggregatum
  • Glomus brasilianum
  • Glomus clarum
  • Glomus deserticola
  • Glomus etunicatum
  • Glomus intraradices
  • Glomus mosseae
  • Glomus monosporum
  • Laccaria bicolor
  • Laccaria laccata
  • Pisolithus tinctorius
  • Rhizopogon amylopogon
  • Rhizopogon fulvigleba
  • Rhizopogon luteolus
  • Rhizopogon villosuli
  • Rhizopogon villosulus
  • Scleroderma cepa
  • Scleroderma citrinum
  • Scleroderma geastrum
  • Suillus granulatus
  • Suillus punctatipes
  • Trichoderma harzianum
  • Trichoderma koningii



  • Azotobacter chroococcum
  • Bacillus amyloliquefaciens
  • Bacillus azotoformans
  • Bacillus coagulans
  • Bacillus licheniformis
  • Bacillus megaterium
  • Bacillus pumilus
  • Bacillus subtilis
  • Bacillus thuringiensis
  • Paenibacillus durum
  • Paenibacillus gordonae
  • Paenibacillus polymyxa
  • Pseudomonas aureofaceans
  • Pseudomonas fluorescens
  • Saccharomyces cerevisiae