Working on a bonsai
A cut on a bonsai is visible for decades, so the tool and where you put it matter more than they do anywhere else in a garden.
Three tools do almost everything
A pair of bonsai shears for foliage and thin shoots. A concave branch cutter for removing anything woody, because it leaves a hollow that heals almost flush instead of a stub. A root rake for combing out a root ball at repotting time.
With those three you can maintain and repot a tree for years. Jin pliers, knob cutters, trunk splitters and wire cutters are all real tools for real techniques, and they are techniques a first tree does not need.
- Shears
- Foliage, thin shoots, deadheading. The tool that gets used every time you look at the tree.
- Concave cutter
- Anything woody. It hollows the cut so the wound heals flush rather than leaving a visible stub.
- Root rake
- Combing a root ball apart at repotting. Pulling instead tears the fine roots the tree lives on.
- The rest can wait
- Not because they are gimmicks. Because they belong to techniques a first tree is years from.
Why a concave cutter rather than secateurs
Ordinary secateurs cut flush or leave a short stub, and on a small tree either is permanently visible. A concave cutter has curved jaws that remove a shallow hollow below the surface, so as the wound closes it fills level with the trunk rather than leaving a bump.
On a full sized tree this would not matter. On a 300mm trunk that will be looked at closely for thirty years it is the difference between a tree with a history and a tree with scars.
- It cuts below the surface
- A shallow hollow, so the wound closes flush instead of over a stub.
- Scale is why it matters
- A 5mm bump on a 300mm trunk is prominent. On a real tree nobody would notice it.
- Knob cutter for bigger removals
- Rounder jaws that take a deeper hollow, for a branch stub already left too long.
- Sharp, always
- A crushed cut on a bonsai dies back further than a clean one, and that dieback is permanent.
Repotting is root work
A bonsai stays small because its roots are periodically combed out and trimmed, not because it is starved. At repotting the root ball is teased apart with a rake or a hook, the circling roots are cut back, and it goes into fresh free draining soil.
The rule is to comb rather than pull. Fine feeder roots do the actual work of keeping the tree alive, and pulling a root ball apart strips them off while leaving the thick anchoring roots that do very little.
- Comb, do not pull
- A rake or a single hook teases roots apart. Pulling strips the fine roots the tree feeds through.
- Trim the circling roots
- Roots spiralling the pot will strangle the trunk eventually. They come off at repotting.
- Free draining soil
- Bonsai soil is mostly grit and akadama rather than compost. Ordinary compost holds water and rots roots.
- Timing matters
- Early spring before growth starts for most species. Repotting in full leaf is a real setback.
Wiring, and taking it off in time
Wire is wrapped around a branch to hold it in a new position while it sets. The two errors are wrapping too tightly, which marks the bark immediately, and leaving it on too long, which is worse: the branch thickens and the wire cuts a permanent spiral scar into it.
Check wired branches every few weeks in the growing season. On a vigorous tree wire can start biting in six weeks. The cut is not reversible, and it is the most common way a beginner damages a tree.
- Firm, not tight
- Enough to hold the position. Tight enough to mark the bark is already too tight.
- Check every few weeks
- On a vigorous tree wire bites within six weeks, and that scar is permanent.
- Cut it off, do not unwind it
- Unwinding snaps the branch you spent a season positioning. Wire cutters, every time.
- Aluminium for a first tree
- Softer, easier to apply and remove, and far more forgiving than copper.
Buying tools rather than a set
A ten piece boxed set costs about the same as three good individual tools, and the three will be better and will be the three you use. Sets are priced on piece count, which is the same trap as every other tool category on this site.
For steel, black carbon steel takes and holds a finer edge and needs drying and oiling. Stainless is easier to look after and slightly duller. Either is fine; a pressed and riveted tool with a stamped blade is not.
- Three tools, bought properly
- Shears, concave cutter, root rake. It costs what a ten piece set does and works far better.
- Carbon or stainless both work
- Carbon takes a finer edge and must be dried. Stainless is easier and slightly less keen.
- Avoid pressed and riveted
- A stamped blade riveted into a handle will not hold an edge or stay in line.
- Clean between trees
- Pruning tools carry disease. A wipe of disinfectant between trees costs nothing.
Frequently asked questions
- What tools do I need for bonsai?
- Three to start: a pair of bonsai shears for foliage, a concave branch cutter for anything woody, and a root rake for repotting. Add wire cutters once you begin wiring. A ten piece set costs about the same and most of it is for techniques a first tree will not need.
- What is a concave cutter for?
- Removing a branch with curved jaws that take a shallow hollow below the surface, so the wound closes flush with the trunk rather than over a stub. On a 300mm tree a small bump is prominent and permanent, which is why ordinary secateurs are not used for this.
- Are bonsai tool sets worth buying?
- Usually not. They are priced on piece count, so most of the contents are for advanced techniques, and the quality of the three tools you will actually use is lower than buying those three individually for about the same money.
- What is the difference between a concave cutter and a knob cutter?
- A concave cutter has jaws curved in one plane, taking a shallow hollow when removing a branch. A knob cutter has rounder, more spherical jaws that take a deeper hemispherical bite, which suits removing a stub or a knob that has already been left too long.
- How do I repot a bonsai without killing it?
- Comb the root ball apart with a rake or hook rather than pulling it, since pulling strips the fine feeder roots the tree lives on. Trim the circling roots, use a free draining bonsai soil rather than compost, and do it in early spring before growth starts.
- How long should bonsai wire stay on?
- Until the branch holds its position, checking every few weeks. On a vigorous tree wire can begin biting into the bark within six weeks, and that leaves a permanent spiral scar. Always cut wire off with cutters rather than unwinding it, which snaps branches.
- Can I use ordinary secateurs on a bonsai?
- For thin green shoots, at a push. For anything woody, no, because they leave a flush cut or a stub and both are permanently visible at bonsai scale. They are also usually too large to get into the position a cut needs to be made from.
- What soil do bonsai need?
- A free draining mix, usually mostly akadama, pumice and lava rather than compost. Ordinary potting compost holds too much water around a confined root ball and roots rot. Free drainage is the single most important thing about bonsai soil.
