Tag Archives: Fundamentals of Bonsai

Fundamentals of Bonsai – Pruning

There are hundreds of questions on bonsai forums, at clubs, and across the globe about pruning. What to prune, when to prune, why we prune, which species can I prune now, how often do I prune, etc. I want to help clarify these questions.


I’ll start with explaining why we prune. There are 3 main reasons to prune:
  • Cleaning
  • Controlling Growth
  • Improving Structure
     We clean to improve airflow and allow sunlight to penetrate into the interior and lower branches. This is also a precursory action to wiring and styling the tree. Trying to wire a tree without cleaning it first can be miserable, especially when doing it on a needle juniper.  Cleaning consists pruning off weak interior growth with little to no ramification and  clearing any foliage in the crotches between the trunks and branches. This includes leggy branches that are not developing in the desired direction.
     Pruning is the way we control growth on our trees. This is how we tell the tree to direct more resources towards a specific branch or section of the tree. This helps to keep your branches a specific length or thickness and give them directional movement to draw interest. This is also the technique we use to gain width in certain branches and keep others from thickening too much. I will go into more detail later on how to do that.
Structural pruning is the way we improve taper, inverse swelling (taper), direct the line of the trunk and branching, and remove flawed or unnecessary branches. Being able to prune effectively is the foundation of successful bonsai practice and design.


Before we go pruning anything we need to step back and observe a few things about the tree we’re about to prune. We need to identify:
  1. What species is the tree?
  2. What is the tree’s current health?
  3. Did you repot the tree within the last few months?
  4. Why am I pruning?
  5. Is the ______(tree, branch, etc.) that I’m about to prune in refinement or development?
  6. What season are we in?
  7. What is the effect on the tree’s energy and health if we prune now?
1. Some species hold significant amounts of energy in certain parts of the tree. Junipers hold significant energy in the foliage. When someone interested in bonsai buys a juniper and then prunes a lot of the foliage off they frequently die, this is why. Pines hold their energy in the roots. Deciduous trees hold theirs throughout the tree. Other species have certain timing for an additional flush of growth (Japanese Black Pine) or timing to prune for flowers.
2. If the tree is not healthy, don’t do any work on it unless it involves solving the health issue.
3. If you recently repotted the tree you should avoid pruning so that the foliage mass can help restore the root system that you worked on.
4. The purpose of pruning can include any of the aforementioned reasons – improving structure, controlling and directing growth, or cleaning.
5. We need to understand the stages of bonsai. If you’re not sure what stage your tree is in do some research before.
6. What season we are in can be a great factor in determining if we can prune without damaging the health of our trees. With most coniferous, deciduous, and broadleaf evergreen species the seasons function in the same way. Winter is a period where the tree doesn’t metabolize freely and we often refer to it as dormancy. Spring is a period of heavy growth. There are several periods of using the trees resources to produce more growth, then gaining those resources back through photosynthesis. In Summer some trees can go into a Summer dormancy if the temperatures get above 90° regularly. If you are in a more mild climate your trees may not slow down growth completely. Fall is a time where the trees save energy and focus on thickening branches and roots to help with Winter hardiness.
7. An example of a bad time to prune would be in Spring right after your tree has pushed out a ton of new leaves. If you prune the branches off before the leaves have been able to form a cuticle (finish growing) and reaccumulate energy, then you’re weakening the tree by taking away its ability to gain energy back.
A generally safe bet is the prune in early Spring before buds pop open or additional candles / needles start growing.
I’d like to also state that you can operate outside of these general guidelines, and depending on how you care for your tree afterwards, you can prune at almost any time. However, I would not recommend pruning whenever you please without extensive knowledge and experience.

Fundamentals of Bonsai: Fall

Fall is an important time in bonsai. This is where we direct our trees to do as we please. Fertilization, future cold hardiness, and girth in branches and trunks all come during this time.

Vascular Growth

Vascular growth is what the tree focuses on in the Fall. This means that producing leaves is not the priority since we aren’t going to be photosynthesizing much in Winter. All energy accumulated from the photosynthetic process go to storage in the trees cells. This energy accumulation is what drives the Spring flush of growth. Different species store their energy in different places. Pines are typically in the roots, Junipers are in the foliage, and Deciduous trees are evenly spread in the roots, trunk, and branches.

Cold Hardiness

There is also an important nugget of information about cold hardiness. In bonsai we love the highly ramified branches. In order to get those twiggy branches we reduce the cold hardiness of that branch. The more sugars and starches we have inside the branch of a tree, the lower the freezing temperature is. Therefore, highly ramified branches are highly susceptible to cold damage even though the tree as a whole might be able to withstand a much colder temperature.

Energy Management

Energy management is of supreme importance in the Fall. The more you fertilize the more energy the tree stores. When a tree has a lot of energy it produces long internodes, large leaves, and coarse thick branching. When a tree has a small amount of energy it produces short internodes, smaller leaves, and fine twiggy branching.

This is why following blanket statements about fertilization can be so dangerous. If you just fertilize every 4 weeks with a full dose every year, you’re never going to be creating a tree with highly ramified branching and small leaves.

Wire Bite

If your tree is wired, this season must be a watchful one for you. Wire bite on the branching of trees most commonly happens in the Fall due to the trees focus on vascular growth. Checking the branches frequently allows you to stay ahead of the trees growth and remove wires before it damages the branch.

Fundamentals of Bonsai – Spring

Spring is when the tree wakes up from its dormancy in Winter. The daylight length and temperatures increase and this signals to the tree that it is time to wake up. The tree then begins a cycle that it follows through Spring.

Juniper Chinensis Bonsai Shohin

  • Buds begin to swell

  • Leaves emerge and the tree goes into an energy deficit.

  • The first flush of growth hardens off and tree goes into energy positive

The perfect time to repot is while the buds are swelling. While the timing cannot always be perfectly right before the buds break, the closer to bud break (without repotting AFTER the bud break) the better.

When leaves emerge the tree spends some of the saved up energy from Fall to produce foliage with the possibility to generate more sugars and starches. When this happens the energy “bank” so to speak, goes negative. The new leaves are like an investment. Until those leaves harden off and form a cuticle, they do not photosynthesize. Until this happens this investment is a negative overall.

Pruning too much at the wrong time, defoliating, a hard freeze that kills foliage, pest issues that grow out of control, and even missing a day or two of watering can do a significant amount of damage to your tree’s health. While it doesn’t always end in a dead tree immediately, you need to consider this in the long term. You might have a hard freeze one year, prune a little off at the wrong time each season, defoliate in the Summer, and then after a few years you find your tree dead for what appears to be no specific reason.

Cotoneaster Repot Bonsai

This guy died from a late freeze after the first push of growth. I had recently repotted it and it was weak due to that. It never made it out 😦

A better way to understand this is to think of investing a significant portion of your savings into a stock hoping for a consistent return of maybe 7%. Instead of return, your stock plummets and becomes worthless. To be able to do anything with your money you’re going to need an amount of time to recoup the money you lost. If you continue as if you hadn’t lost all of your money in the investment and then spend with the intention to withdraw your invested money, you’ll be negative because you don’t actually have that money. If you have a tree that loses leaves from a freeze and then pushes out new leaves, the tree will have less energy in the bank. If you proceed by delofiating it to get a smaller push of leaves, you’ll find that it doesn’t have enough energy and will possibly die.

The vigor of the growth, length of internodes, size of leaves, and amount of leaves all depends on what you’ve previously done.

Fertilizing frequency and strength play a large part in Spring growth. If you’ve been fertilizing heavily and at the maximum frequency, you’re bound to have a large amount of energy. This will result in a lot of leaves, larger leaves, and longer internodes. The pot size also has an effect. If you fertilize lightly and infrequently, but you have your tree in a large training pot, you will not see small internodes or small leaves. Restricting the area for the roots to grow creates less vigorous growth.

If you’ve repotted a deciduous tree and pruned a large amount of roots, you’ll only see the amount of leaves that the roots can support. For a photo of this see this blog post about the difference.

Let’s go over what we’ve learned:

  • Daylight length and temperature determine when a tree breaks dormancy

  • Fertilizing strength and frequency (are not the only factors, but major factors) correlate with internode length, leaf size, and leaf quantity.

  • A deciduous tree will only push out growth that it can support with its root system.

  • Fertilizing can be throttled with frequency and strength.

  • Energy for Spring growth is stored by the tree in Fall

  • Repotting is best done before the buds break at the beginning of Spring.

  • New leaves take energy to produce and then produce energy when they harden off.

  • Common bonsai techniques (repotting, pruning, defoliation, watering, etc.) performed at the wrong time or late freezes can damage your tree’s health.

Japanese Maple Leaves

Fundamentals of Bonsai – Terminology

Bonsai Shohin Display

Understanding the terminology of bonsai can help you from getting lost when trying to understand more advanced discussions.


Trident Maple Bonsai

  • Air-Layering – a technique to create roots at a new part of the tree. This is used as a propagation method and used to replace the existing root system.

  • Akadama – a Japanese native soil that allows roots to penetrate and grow through the particles

  • Apex – the highest point of a tree that can include a single branch or a small group of branches

  • Apical – most vigorous growth produced by a tree that is typically at the end of a branch or at the upper canopy.

  • Back Budding – a technique to encourage growth further back along the branch or trunk by pruning the apical growth.

  • Bud Break – the point at which the bud has opened enough to show a green tip.

  • Branches (Primary, Secondary, Tertiary) – Primary branches grow directly from the trunk; Secondary branches grow directly from the Primary branches; Tertiary branches grow directly from the Secondary branches.

  • Broad-leafed Evergreen – Trees with leaves that are broad that do not change color and fall off during Autumn.

  • Conifer – Trees with needles or scale-like foliage that are evergreen.

  • Bud – organ or shoot containing an embryonic branch, leaf or flower.

  • Cambium – green growth tissue directly below the bark; it’s increase adds to the girth of roots and stems.

  • Callous – tissue that forms over a wound on a branch or trunk as part of the healing process.

  • Candle – name given to the extending bud of a Pine tree before the new needles open.

  • Chop – heavy pruning and height reduction of the tree trunk.

  • Deadwood – a special technique used to create deadwood on a Bonsai which enhances the character of and, ages the appearance of a tree.

  • Deciduous – broad-leaved trees which harden off and shed their leaves in the Autumn followed by dormancy during the Winter.

  • Defoliation – removal of all or most of a tree’s leaves to reduce leaf size and vigor of growth.

    Japanese Maple Bonsai Display

  • Die Back – death of growth beginning at the tip due to disease or injury.

  • Evergreen – a plant that remains in leaf year round, slowly shedding old leaves while being replaced by new growth.

  • Form – the main direction in which the trunk of a tree grows.

  • Graft – a technique used to meld or attach a branch to the stump of a tree.

  • Internode – the section of growth between two nodes (leaves or leaf-joints).

  • Jin – removal of bark on a branch to create deadwood.

  • Mame – Bonsai trees less than 6″/15 cm in height.

  • Nebari – the flare of the roots that sometimes creates a mound.

  • Node – growth point on a branch or trunk from which leaves, leaf-buds and shoots can appear.

  • Petiole – the stalk of a leaf that attaches the leaf to the branch.

  • Phloem – a layer of the branch that is used to transport fluids and nutrients

  • Pre-Bonsai – a young tree that has not yet been trained.

  • Pruning – most important method in training a Bonsai by trimming leaves and/or branches.Developed Bonsai Specimen

  • Ramification – repeated division of branches into secondary branches by means of pruning.

  • Seasonal Bonsai – a species that look their best for only a short time when in flower or fruit.

  • Shari – technique used to create deadwood on trunk.

  • Shohin – name given to Bonsai less than 18″/45 cm in height.

  • Soil – the growing medium used for Bonsai. Typically made of mostly inorganic substrates

  • Sphagnum Moss – general name given to a long fibred moss used as an organic soil component for Bonsai and air-layering; has a great ability to absorb and hold moisture.

  • Style – the way in which a Bonsai has been shaped in order to compliment the form (direction) of the trunk.

  • Substrate – the growing medium in which a plant grows.

  • Terminal – apical; outermost tip.

  • Terminal Bud – a bud formed at the tip of a stem, twig or branchlet.

  • Trunk Leader – uppermost branch on a previously cut off trunk that is trained to grow vertically as an extension of that trunk.

  • Wiring – a technique using wire to bend a branch or trunk in a certain direction thus training it to grow in that way.

  • Xylem – area below the cambium layer in a trunk.

  • Yamadori – material collected from the wild.

Fundamentals of Bonsai – Basic Physiology

There is a lot of confusion when you begin the bonsai journey. You’ll hear suggestions from everyone about how to do everything. One thing that helps is understanding why you’re doing something. Understanding the physiology of your plants will help dramatically with that.

I wanted to start with this photo that has a bit of information. You don’t have to memorize this to practice bonsai by any means, but I’ll go over the important parts.

Plant Physiology

Koning, Ross E. 1994. Plant Basics. Plant Physiology Information Website. http://plantphys.info/plant_physiology/plantbasics1.shtml. (6-2-2018)

Trees need 4 things to survive:

  • Water

  • Sunlight

  • Air

  • Nutrients

The Leaf

Leaves are responsible for the sunlight and movement of water. Leaves photosynthesize and send the sugars and starches created to the plant via the phloem. As water evaporates in the leaves the process of transpiration occurs. Transpiration in essence “pulls” a chain of water molecules from the roots up to the leaf to replace the loss of water. The cuticle is a waxy covering on the leaf that stops moisture loss once the leaf has fully “developed.” Once a leaf has its cuticle it begins photosynthesizing and accumulating energy. This happens once a leaf has reached its mature size after breaking out of the bud, changed to a darker color, and has become less flexible.

There are several techniques used in bonsai that involve leaves, namely: full and partial defoliation, leaf cutting, pruning, watering, development of branches and trunk, and allocation of resources throughout the tree.

Branches are like roads, the more they are used the bigger they get. If one branch has 20 leaves and another has 5, the branch with 20 leaves will thicken quicker than the branch with 5 leaves. This is because more energy is being created and more water is being moved there from the water loss of the leaves. We learn from this that foliar mass = girth.

The Roots

Roots are responsible for the uptake of water, oxygen and nutrients. There needs to be a balance of water and oxygen in the soil for this to take place and not starve the plant for either water or oxygen. Roots move water and nutrients to the plant through the xylem.

Large roots help to anchor trees in nature. Small fine roots are the main roots that absorb moisture and nutrients. Roots function the same way branches do in the sense that the more fine roots you have attached to a larger root, the bigger it will get.

In bonsai we repot anywhere from every year to every 10 years depending on the needs of the tree. We prune the roots and style them much like we do to the branches above the soil line.

The Stem

The trunk and branches have bark which aids in retaining moisture. I’ll talk more about the stem as needed in further discussions, but what you need to know is: the xylem moves water and nutrients from roots to leaves, phloem moves energy to the tree from the leaves, and cambium helps the tree get thicker and indicates the tree is still living by showing a green tissue layer under the bark.

Wiring and bending a tree can be more difficult depending on the species of the tree. Different species have varying abilities to bend, and this is due to the changes in the xylem, phloem, cambium, amount of water moved (water loss due to transpiration), and bark.

Deciduous Root Pruning Effects

During the early Spring I purchased two cotoneasters from the discount rack at Lowe’s. I took one of them and repotted it and slip potted the other one into a larger container. You can see these photos and notice that the cotoneaster on the right has significantly more foliage than the root pruned cotoneaster on the left.










This is how deciduous trees respond when root pruned. They will not put out more foliage than they can support with the root system and stored up energy from the previous Fall.

Fundamentals of Bonsai – Stages of Bonsai

Many people want to immediately put a plant in a bonsai pot. Lets face it, who wouldn’t? It looks really cool. Hence our love of bonsai. Realizing what stage your tree is in before making rash decisions will help you receive a more long term satisfaction as opposed to the few days of glee before you kill your tree.

There are 2 stages that different parts of your tree can be in: Development and Refinement.

Development typically includes

  • Energy accumulation and heavy fertilizing

  • Taper of the trunk and branching

  • Primary and secondary branching structure

  • Building root systems and nebari

  • Healing large wounds

Refinement typically includes

  • Controlled energy accumulation through regulated fertilizing

  • Tertiary branching (aka ramification)

  • Leaf size reduction

  • Bonsai container

  • Shorter internodes


Trunk Thickness

The trunk thickens with time. The easiest way to think of this is to know that the more leaves on the tree, the faster the trunk will thicken. This allows more sugars and starches to be produced by the leaves. The vascular growth of the Fall is then able to store more energy and create a thicker trunk or branch.

Trees are typically grown in the ground (or called “Field Grown” trees) to maximize the speed with which the trunk grows by energy accumulation. By not limiting the potential root system you allow for faster development. This means if you put your tree in a bonsai pot you will not experience a thickening trunk. While it will thicken, it will take anywhere from 3 to 10 times as long to accomplish a thickness compared to putting it in the ground or in a larger training pot.

Trident Maple Bonsai

Planting the tree in the ground ontop of a tile or a flat surface allows the roots to grow outward instead of downward which will result in a better nebari in the future, and the ability to be in a shallow pot when the refinement stage is at hand.

Another common technique used with certain species is called trunk chopping. This technique involves letting a tree grow a significant amount and chopping a large amount (typically 50% or more) of the trunk off and letting a new branch become the “leader” or the new trunk. This is how you acquire large trunks like this Trident Maple.

Developing Taper:

Taper is created by having the branch or trunk grow out and pruning back to a branch that is thinner than the current branch. This photo courtesy of Bonsaiexperience.com illustrates the process:

Trunk Taper Pruning

This is done with both the development of the trunk and the development of primary branches. To give your tree the appearance of age you need to incorporate taper.

Primary and Secondary Branching:

Your tree does not leave the development stage completely until you have primary branching that you’re happy with. Developing those branches at a size that is proportional to the trunk will take a solid amount of growth that won’t come as quick in a bonsai pot undergoing refinement.

Nebari and Root Systems:

Regularly pruning the roots over the years gives you the opportunity to develop the radial roots and remove any downward growing roots.


Energy Management:

Fertilizing too heavily while trying to refine your tree will lead to a tree that is well below its potential. To get shorter internodes and smaller leaves you have to give the tree just enough energy to push out a little bit more.

This idea is perfectly demonstrated by defoliation. You cut off the trees ability to produce energy, so naturally it says “I need those!” and responds by putting out new leaves. The catch here is that the tree doesn’t have as much energy (or any potential to create more energy) and therefore puts out smaller leaves. If you follow up by fertilizing heavily, the next Spring you’ll observe larger leaves.


This comes by pruning the tree regularly to a point where it branches out or where there are multiple buds. This can be problematic when heavily fertilizing the tree as is needed in development stages.

Wiring Ramification Bonsai


Leaf sizes can be reduced when desired on certain species by removing the foliage. This uses the stored energy in the tree to push out another flush of growth that cannot reach the same size of the previous leaves. This also can be problematic if you’re heavily fertilizing.

Internode Length

This happens when you decrease the fertilizer and overall energy the tree has. Inserting the tree in a bonsai container also helps with this as it limits the overall vigor the tree can amount.

Bonsai Container:

Restricting the root growth on a tree is one part of smaller internodes, smaller leaves, and refined branching. If you’re trying to refine part of your tree and develop another, you’ll have a hard time getting any thickening in a certain point in comparison to others.