I have a fair number of primarily deciduous trees (Tridents, Japanese maples, elms, crabapples,etc.) planted outside in rows for development of trunk diameter. I live in Oregon in the Willamette Valley which I think is about zone 8b. The majority of them have been in place for 3-5 years and allowed to grow. I've only stepped in when I'm concerned about reverse taper, to change trunk direction, or I want to spur some lower trunk branching. Many of them are planted on tiles or bricks. They are starting to develop some nice trunks and over the next few years I will be digging them up and working on their roots (removing ugly roots, encouraging feeders, etc.) and then replanting them for more development. I'm trying to decide if spring or fall would be the best season for this work. Spring seemed obvious at first but we have a dry season in the summer and many of these trees aren't irrigated. Fall could work (plenty of rain) but they might be vulnerable to colder weather. When would you work on them? I realize the question is inherently flawed because there are lots of different species here but does anyone have opinions, guidelines, past experience. I've been waiting on these a while and don't want to muck them up if I can help it.