Bonsai Cutters: Bonsai Knob Cutter vs Concave Cutter

  • By: Josh Koop
  • Date: February 8, 2023
  • Time to read: 5 min.
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The bonsai kit tool usually comes with a variety of cutters in it. The differences range in size, shape, and function.

Although some might seem very similar, it will take only a professional to understand and make use of the difference.

You will end up with an unpleasant outcome if you use any bonsai tool without having a proper understanding of how it works and what size of a tree or branch it cuts.

We understand that there are a couple of people out there who have difficulties distinguishing between some of these tools.

In this article, we have picked the bonsai knob cutter and the concave cutter to bring out their differences and similarities. We urge you to stay focused and gain expert knowledge about these two tools.

As a reminder, the two tools are both used for cutting but what matters is the size and part of each tree used for cutting. 

Let us take a look at some differences and similarities.

What material are they made of?

Before buying a bonsai knob cutter, you must verify what material it is made of so you can know what to expect. Carbon steel and stainless steel are the two common materials used to manufacture knob cutters. So, choose:

– Carbon Steel if you want your tool to stay sharper for a longer amount of time. Just be aware that you must take precautions to prevent your tool from rusting.

The Stainless Steel variant is for you if you want your tool to be rust-free and require little maintenance. However, Stainless Steel tools will get blunt more quickly than carbon steel tools.

What do they look like (shape)?

The two tools are much more similar in shape. The knob cutter’s cutting blades have the shape of two halves of a sphere that open and close, but the edges of its blades are much more rounded, and this shape allows it to bite into the wood with vigor.

The concave cutter has a similar design as the knob cutter (spherical), but its blades are pointed and cut branches flush to the trunk.

What are they used for? 

Although they have similar shapes, they perform different functions, as shown below.

  1. Bonsai knob cutter. The primary function of a bonsai knob cutter is trimming larger limbs close to the tree trunk. The knob cutter has rounded jaws that help it chop gradually into the tree, making concave cuts that heal quickly and smoothly. Another useful feature of the knob cutter is its long handles. 

The long handles ease your work in an area with thick woody branches.

You can also use these cutters to progressively make deeper, smaller bites when making tricky or drastic cuts requiring a cautious approach. 8 1/4″ long overall.

The knob cutter is similar to the concave cutter but has a few additional features.

  • The knob cutter’s cutting blades are formed like two halves of a spherical. The tool’s form allows it to bite into the wood with vigor.
  • The knob cutter easily and swiftly nibbles away at protruding stubs in a regulated manner. It can rapidly remove a large amount of wood while maintaining adequate precision.
  •  This tool can also remove unwanted root or trunk material from around a partially severed tap root. The strong nibbling ability easily removes superfluous callus behind the trunk, where other tools are difficult to use due to a lack of space.
  • The concave cutter aids in cutting, particularly for cutting off whole branches of a bonsai tree.

The concave cutter leaves a slightly curved cutting area and produces a clean cut that heals quickly.

This pruner comes in various sizes and quality grades and is meant to prune entire branches.

In bonsai, the concave cutter is considered one of the “heavy” tools.

 But you won’t be needing it during lesser trimming sessions. It can cut up to 10mm in green words and is essential for pruning.

The concave cutter can cut right into hard-to-reach areas of a dense tree, an advantage you won’t have when using a knob cutter.

Do their prices differ?

The price for a knob cutter is not the same as that for a concave cutter. Although price is not a suitable parameter to suggest any difference or similarity between a knob cutter and a concave cutter, it is still worth mentioning.

We advise you not to capitalize on price in comparing these two tools because there exist different sizes of each and with different prices.

The price might also vary from shop to shop and may be from seasoning to seasoning. 

When do you use a knob cutter?

The knob cutter can also remove unwanted root or trunk material from around a partially severed tap root.

The strong nibbling ability easily removes superfluous calluses behind the trunk, where other tools are difficult to use.

When do you not use a knob cutter?

Because of its roundedness, a knob cutter cannot reach some end of a dense tree. Using it here will be a stressful job to achieve.

When do you use a concave cutter?

This is the tool to use if you need to cut off larger and complete branches. When you need to prune a branch near the trunk and don’t want scar tissue to grow on the cut, the concave cutter comes in handy.

Of course, no guarantees can be made, but employing the concave cutter will result in a clean cut that heals quickly and leaves little to no scar.

When do you not use a concave cutter?

Don’t use the concave cutter if you want to make scar tissue on your bonsai tree’s branches or trunk. Also, avoid using this instrument on smaller twigs and branches.

Smaller twigs and branches require smaller tools such as scissors, so you will minimize the risk of hurting yourself or the tree by avoiding concave cutters.


There is no wonder why these two tools are indispensable in bonsai training. Even though they have differences and similarities, a complete bonsai cannot be achieved using one without the other.

Each contributes uniquely to the final result of every bonsai you have ever seen.