Have you seen a tree branch coiled with bonsai wire?
In bonsai art, wire is one of bonsai supplies used to hold bended branches and small trunks of trees to desired position. The trees can adapt and, in a few weeks or months, their wired trunk and branches still stay in position even after the wire is removed.
To bend trunk and shapes of bonsai trees, basically, we can use any wire of common metals that is capable of being bent without too much effort and being removed easily later on.
Bonsai fanciers do not usually use iron or steel wire due to its features of rusty and over stiffness. Besides, iron and steel are poisonous to Junipers and some other coniferous species.
Meanwhile, both copper and aluminum wire have been commonly used in bonsai wiring, though some people prefer aluminum to copper wire, and vice versa.
Annealed copper wire is harder and suitable for trunks and large branches. It has the unique physical property of increasing its stiffness upon being flexed, which is call “work hardens”. Annealed copper wire is soft enough to bend comfortably the first time. Yet, as it is coiled around the branch, annealed copper wire become much stiff, giving better holding power. Thus, once being coiled into position, it can’t be un-coiled. Instead, you must need a wire cutter to remove copper wire.
Aluminum wire is softer and we need larger diameter of aluminum wire to have the same holding power. Accordingly, it has been most popular in doing lighter wiring, especially on soft-barked trees like maples and azaleas. This type of wire is also easier to apply for beginners and can be re-used, thought that’s not recommended.
Many bonsai artists, especially Japanese, often recommend wrapping wire by spiraling strips of light paper around it as protection for the tender bark of sensitive plants such as maples. In my country, we use wire wrapping with soft cotton strings.
Typically, you will need a wire thickness of a 1/3 that of the trunk or branch you are trying to bend.
Keep in mind that using wire that’s a little heavier than you really need will always work better than using wire not strong enough to hold things where you want them. Of course, if the wire you used wasn’t strong enough, adding another wire or two parallel and close to the first will often work.
You can get wire at hardware shops but that’s usually not wire designed for bonsai. You can easily buy specialist bonsai wire from nurseries, bonsai malls, or online shops.
Aluminum wire available in two types, plain (silver), and anodized, where the wire is given a brown coating. It is sold in millimeter thickness. The thicker the wire, the stronger it's holding power.
Copper wire is available in annealed form, and sold according to its gauge or sometimes millimeter.
You will need 3 or 4 different thicknesses to fully wire a tree; try buying reels of 1mm, 1 1/2mm, 2 1/2 and 4mm to start with. As you gain experience you will be able to identify exactly which sizes you tend to use for the size and species of bonsai you are wiring.