There are two choices when it comes to bonsai wire, and both have advantages and disadvantages. So how do you choose between copper and aluminum?
The key to deciding is knowing what the advantages are of each, and deciding which presents the best circumstances for your bonsai and its environment. Let's review the differences between copper and aluminum, as well as some of the fundamentals when it comes to healthy wiring for your bonsai tree.
Why (or why not) copper?
Annealed copper has a few advantages over aluminum. It has more holding power for a given diameter than aluminum, and hardens as it is applied. It is also more aesthetically pleasing as it weathers, and is more economical. Copper is also preferred for conifers.
However, copper is more difficult to apply than aluminum, which can present challenges for newcomers to bonsai. Because it work-hardens quickly, there isn't a lot of time for a novice to try and try again. Also, copper must be annealed before it is used, and must be re-annealed in order to be re-used.
Why (or why not) aluminum?
Besides being softer, easier to apply, and more easily re-used because it doesn't harden, anodized aluminum doesn't require annealing before each use, as copper does. It also leaves less scarring on the tree.
However, aluminum has less holding power than copper for a given diameter, which means it requires a heavier gauge, and is more expensive to use. Anodizing also tends to fade with exposure to sunlight, taking on a bright, often unappealing aluminum color.
Finally, both aluminum and copper can present health challenges to your bonsai. As copper ages on a tree, it turns a darker, less obtrusive color. But it can also develop a green patina caused by oxidation. This condition, called verdigris, can be harmful to some types of trees, notably fruits. On the other hand, aluminum can be toxic to some types of trees if it is not properly anodized. So we'll consider this a push.
The size of your wire:
Bonsai wire is available in sizes between 1 and 6 millimeters. While there is no rule for what gauge of wire you should use, it is suggested that your wire be one-third the thickness of the section to be wired. Also, if you expect to have to make a drastic bend, a heavier gauge is required. In this case you may want to consider using multiple wires. It will require smaller wire gauge, but also more patience.
Be sure and check out how much wire you need - Bonsai Wire Conversion Chart
The best time to wire:
Most bonsai experts recommend that your tree be wired in late winter or early spring, but wiring can be done at almost any time of year. Generally, however, major wiring is done at the time of pruning for easier access.
Here are some seasonal tips to keep in mind. Spring is when your bonsai starts its active growth cycle, which means it is easier to break a delicate branch or damage soft bark during wiring. Careful monitoring is requires to ensure wiring is not cutting into the tree.
In the summer, the cambium is full of sap, making it easy to cause separation of the bark from the wood if drastic bends are made. Smaller branches are hardened, though, making them easier to wire. Keep in mind, however, that foliage will likely get in the way.
Autumn is not recommended, simple because your bonsai is starting to set new buds for next year's foliage. The ideal time is winter. No foliage is in the way, and the wire can be left on longer without risk of scarring. Just be cautious not to knock off next year's buds, and be aware that the smaller branches can be brittle.
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