Generally, the usual time to do wiring is during spring to summer. Growth rates are supposedly highest during this period, resulting in quick recovery of the branches from internal splitting caused by the bending of branches. But for tropical trees, wiring can be done at any time of the year, as there is no set season for faster or slower growth.
For deciduous trees, wiring in late autumn may be easier to accomplish. The shedding of leaves should enable easier execution of wiring. This creates a more visible work area for your hands and fingers. For summer time wrapping of conifers, don’t let your wires overlap the needles on the branches.
Between individual trees, growth rates are often different, and therefore it’s hard to predict when exactly they grow dormant, even though the season and climate may have changed. Some deciduous trees are more delicate in the spring, when their growing season begins and sap begins to flow. You may consider wiring during summer, when the sap levels are lower.
Waiting too long has its disadvantages as well. As mentioned earlier, growth rates are usually highest during the spring-summer period. By not wiring during this time zone, you may lose out on periods when the growth is really fast. Should you find that you made mistakes later on, you would have then no time to remedy your action. Wiring during winter may produce nil results, because of lack of growth during this period.
The species being wired would also affect the timing of the wiring. Pine wired in autumn, for example, can easily experience scarring if the wire isn’t checked every couple of weeks, because they actually grow fast during autumn time, stretching through the winter.
Before you wire your bonsai tree, read up on the particualr species’ requirements, and timing of its seasons before going ahead. Wiring is best for younger trees, as they can be “bendable” due to high growth rates. For older trees, great care is required to avoid stretching the tree pass its limits.