The dormant season may be a fine time to wire deciduous trees, as well as most conifers. It is not without importance exactly at what part of the season the work is carried out though.
Evergreen Junipers for example have a low sap flow during winter and cope wiring well in this period, as the cells stretch better than when being water filled. As always, everything must done with care, and feeling the flexibility of each branch is important. Overdoing it might cause the branch to snap or risk being damaged. Why it is better to do the bend slowly. Little by little, giving the branch a bend and a pause. After a rest of an hour or so, the next step can be taken, bending a little more.
Take care with deciduous bonsai
Deciduous are different. They tolerate wiring and bending branches well, when the sap flow is reduced late autumn. When the leafs are shredded ideally is the best time to wire and bend. The cells are flexible at that time. Also when the sap flow builds up before the new leaves develops in late winter, is a fine time to arrange the branches.
The worst time for the deciduous bonsai to be worked on regarding wire and bending branches is mid winter. Despite the cells are holding less water, the branches becomes stiffer and may easily break when bend. Therefore the shaping off deciduous trees are best done in autumn and just before spring arrives where the leaf opens.