Bonsai wire is used to start training bonsai, maintain an existing one and to change older bonsai as well.
The wire is wrapped on the branch or trunk the way it is currently growing. It is temporary! Then with fingers on the wire only, bend slowly to achieve a new position.
The two most commonly used types are copper and aluminum. There are several differences between the two.
Copper for bonsai is not the same wire you would find in a home store hardware department.
Common copper wire is
less expensive, however, then it must be annealed (heated) to soften it
for bonsai use. "Copper bonsai wire" has been annealed to make it much easier
to work with than common copper. Always ask if it is annealed!
Copper is sized by its gauge. The lower the number the heavier the wire. The heavier the wire the heavier the use (large branches.) For example - #20 copper wire would be for fine branches. The #12 and #14 are considered the most often used sizes overall.
At first glance aluminum bonsai wire may not look aluminum because it has a bronze-like coating. This coloring is used to help it blend in with the tree. Aluminum sizing is entirely different than copper.
Aluminum is sized in the metric system, starting with 1.0 (which is very small.) In aluminum the most common sizes for beginners are 1.5, 2.0, 2.5 and 3. Large, heavy branches will take higher numbers.
A Note About Metrics - The United States is gradually switching to the
metric unit system. Meanwhile, if you need help determining the size of a bonsai described in inches and vice versa or even the size of your bonsai wire use this
metric conversion table.
The big difference in the two types is, copper 'hardens' once it is on a branch and holds the branch more firmly. Since you can use smaller sizes to do the same job, many prefer copper over aluminum.
On the other hand, if you are using fast growing bonsai trees (such as tropicals,) aluminum is less likely to cut in as quickly.
Different bonsai artists favor different types. Today many artists use aluminum, and it is often recommended for beginners. However, the best wire is the one you are comfortable working with.
When you purchase your first bonsai wire, do not to buy sizes of either extreme ... too small or too big. It is unlikely you will need them.
If you plan to wire bonsai, you should have several sizes on hand. An easy way to tell which size you need is to take smallest size you have, press a small piece against the part of a branch you want to shape.
If the branch does not bend, but the wire does … go to the next size … and then the next size if necessary. Do not press against the end of the branch, that will tell you nothing. Be sure to press near where you want the branch to bend.
Always anchor the wire. If it is not secured in the ground, OR wrapped around the trunk or another branch at least twice before it gets to the branch you want to bend, it's not going to work!
Wiring bonsai is much like braces on teeth. It reshapes or re-positions a branch or trunk by bending it.
This process (like braces) is a temporary procedure ... removed when the branch holds the desired position.
To prevent scaring,
wire is sometimes taken off early, only to be rewired and bent again.
When checking to see if the wire is about to damage the tree use this excellent bit of advice from Florida bonsai artist Ed Trout: "Be sure to look at the heaviest part of the branch first. This is where the initial tightness will show up."
Any type of wire cutters will work. However, bonsai wire cutters are shaped to prevent damage to the bark.
It is tempting to unwind bonsai wire to save money. With copper wire especially, this is a bad idea. You may easily damage or break a small branch or even gouge the trunk.
Add a pair of these cutters to your bonsai tool collection.
In some instances, pulling limbs down with string or wire, even weighing them down with rocks or fishing weights is a supplemental way to re-position branches.
Frequently, they are used in combination.
Here is a fun page about wire tree sculpture