Pruning and wiring bonsai: when to cut, how to wire and how to avoid wire scars

TUREFF• •0

Pruning and wiring are how a bonsai gets its shape. Pruning decides which branches stay; wiring moves the ones that remain into position. Both are simple in principle, but timing and technique matter, and wire left on too long leaves scars that take years to fade.

Two kinds of pruning

Maintenance pruning keeps the shape. You trim back new shoots that grow beyond the outline during the growing season, which also encourages finer, denser growth.
Structural pruning removes larger branches to set the tree's basic design. It is a bigger step and usually done once in a while, not every week.

When to prune

Maintenance pruning is done through the growing season, as shoots extend.
Structural pruning is usually done when the tree is less active, often late winter or early spring before growth starts for many deciduous species. Timing varies by species, and some conifers have their own rules.
Avoid heavy pruning on a weak or newly repotted tree. Let it recover first.

How to prune well

Step back and decide what you are aiming for before you cut. A branch removed cannot be put back.
Cut back to a bud or leaf pointing the way you want new growth to go.
Remove larger branches with a concave cutter so the wound sits flush and heals flatter.
Keep tools clean and sharp.
For large cuts, many growers seal the wound with cut paste.

A common beginner approach is to remove obvious problems first: branches crossing each other, growing straight up or down, or two growing from the same point.

Wiring: what it does

Wire wrapped around a branch lets you bend it into position. Over time the branch sets, and the wire is removed. It is a temporary tool, not a permanent support.

Choosing wire

Aluminium is softer and easier to work with, and often used for deciduous trees.
Copper holds more strongly at a thinner gauge and is often used for conifers, but it is harder to apply.
Thickness: a common rule of thumb is wire around a third of the branch's thickness, with softer aluminium sometimes thicker. If the branch springs back after bending, the wire is too thin.

How to wire

Wire when branches are flexible; avoid wiring a dry or weak tree.
Anchor the wire first, usually by wrapping it around the trunk or pairing two branches of similar thickness with one length of wire.
Wrap at roughly a 45-degree angle along the branch. Too tight a coil behaves like a spring, too loose holds nothing.
Keep the wire in light contact with the bark, not biting into it.
Bend slowly, supporting the branch with your thumbs on the outside of the curve.
Do not wire over leaves or buds.

Avoiding wire scars

Branches thicken while the wire stays the same size. When that happens, the wire cuts into the bark and leaves a spiral scar.

Check wired branches regularly, especially during spring and summer growth, when thickening can be quick.
Remove wire as soon as it starts to bite, even if the branch has not fully set. You can rewire later.
Cut the wire off in short pieces with wire cutters, rather than unwinding it, which can tear bark or snap the branch.
If a branch springs back after removal, wire it again, preferably in a slightly different path.

Start small

Practise on a cheap nursery plant before your best tree. Wiring well is a hands-on skill, and a local club or workshop is the fastest way to learn. What are you shaping at the moment? Share your progress, or ask about wire gauge or timing for your species, in the comments.