Choosing bonsai wire: gauge and material

Wire is how a bonsai gets its shape. Applied well it is invisible within a season; applied badly it leaves a spiral scar that takes years to grow out and sometimes never does.

Aluminium or copper

Anodised aluminium is softer, easier to apply and remove, reusable within reason, and available in gauges from under a millimetre upwards. It is what almost everyone should use, and it is what almost every set on this shelf contains. The dark anodised finish is nearly invisible against bark.

Copper is harder and holds more strongly for its thickness, which means thinner wire for the same result — an advantage on conifers and on anything where the wire will be visible. It work-hardens as you apply it, so it grips even better once bent, and it is correspondingly harder to remove.

The practical rule: aluminium for deciduous and broadleaf material, copper for conifers and for finished trees where thin wire matters. In this climate, on tropical and sub-tropical species, aluminium covers almost everything.

The one-third rule

Wire diameter should be roughly one third of the branch diameter.

Too thin and the branch springs back and the wire has done nothing but mark it. Too thick and you cannot bend it accurately, and it damages bark as it is applied.

Rough starting points:

• 1.0mm — fine twigs and small shoots
• 1.5mm — secondary branches on a small tree
• 2.0mm — primary branches on a shohin or medium tree
• 2.5mm and up — heavy branches and trunks on larger material

This is why wire is sold in multi-gauge sets. One roll is never enough, and buying four gauges at once is considerably cheaper than buying them one at a time as you need them.

Where one gauge will not hold, two thinner wires side by side hold better than one thicker one and are much easier to apply.

Applying it

The habits that separate a wired tree from a damaged one:

• Anchor first. Wire that is not anchored simply rotates around the branch. Anchor into the soil, around the trunk, or by wiring two branches with one length so each anchors the other.
• Roughly 45 degrees. Shallower and it slips; steeper and it acts as a spring rather than a splint.
• Even spacing, no crossing. Wire crossing itself creates a pressure point that scars.
• Wire first, bend second. Apply along the whole length, then shape. Bending as you go tears bark.
• Bend with the wire on the outside of the curve, supporting the branch with your thumbs on the inside. The wire takes the tension and the branch does not split.

Work from the trunk outwards, from thicker wire to thinner.

How long to leave it on

Until the branch holds its position, and not one day longer.

Timing depends entirely on how fast the tree is growing, and in south Florida the answer is: faster than you expect. A tropical species in a Miami summer can thicken enough to bite in within six to eight weeks. The same species in a northern winter might take a year.

There is no calendar rule. There is only checking.

Checking for bite-in

Look at the wire against the bark every couple of weeks in the growing season. When the wire stops standing proud and the bark begins to swell against it, remove it.

Wire that has bitten in leaves a spiral groove. On some species that scar grows out in a few years. On smooth-barked species it never fully does.

The rule that saves trees: it is always better to remove wire too early and reapply than to leave it a fortnight too long.

Removing it

Cut it off in short sections with a wire cutter. Do not unwind it.

Unwinding puts every bend back through the branch in reverse and is the commonest way to snap a branch that has just spent a season getting where you wanted it. A dedicated wire cutter has a blunt rounded head that cuts against the wire without gouging the bark.

Aluminium can be reused if it comes off in usable lengths and is not kinked. Copper that has work-hardened has to be annealed before reuse, which is more trouble than it is worth for most people.

Storage in a humid climate

Anodised aluminium does not corrode meaningfully. Copper oxidises to a dull brown, which is cosmetic and arguably an improvement.

Keep rolls out of direct sun — UV degrades the plastic spool, not the wire — and keep the ends tucked so they do not unravel in a bag.

Where to look

Wire in multi-gauge kits, with cutters included, is on the training wire page, listed by millimetre and by total length. Wire cutters on their own and with other tools are under cutters and shears and in the sets at bonsai tool sets.