The worst time to do something like this is when the tree is actually growing vigoursly, spring summer. Best done in late fall or winter.

You asking this question tells me that you want an 'instant' large trunk.

The biggest mistake that most beginners make is to pot a tree in a little pot then want it to be a nice finished bonsai...it ain't happenin'. For the first few years it needs to be grossly overpotted or put in the ground, allowed to grow tall and big. The trunk will develop more quickly along with the base. When the trunk size is reached you make a slanting cut to top the tree...on the back where it won't be seen...then work a new apex.

Leaving it in the big container or the ground for another year or so will help the cutting scar begin to heal faster and the apex grow (fatten) quicker and better.

Bob

"Leaving it in the big container or the ground for another year or so will help the cutting scar begin to heal faster and the apex grow (fatten) quicker and better."

What Bob said.

For trunk development, you need free run for the roots. Then you can consider your cuts....but that's still a ways off.

As to the cutting of the outer tissue....I *suppose* some species might produce thick scar-tissue to "fatten" or increase the diameter of the trunk. I have noticed that trees that are hit by bumpers in parking lots will often develop a fat, scarrified base at bumper height. This might be a false correlation, but trauma seems to be the cause of this phenomenon in some cases.

Josh

I should have been more clear on that one. I was refering to when the tree is finally topped and a new apex formed. It will begin to grow over quicker if it's left on the ground for a few years after. You are really right about parking lot trees!

Bob

Yeah, just in case of any confusion.....

Bob is talking about a "trunk chop," which removes the majority of the tree. A new leader is
then selected (from a node near the base) to become the new apex (apical meristem).

Bob,
I definitely squeeze and manipulate some of my smaller trees, just to agitate the trunks a bit
to help root-development, et cetera. Oh, and thanks for confirmation on the parking lot trees!

Josh

True, most people don't realize that wiggling the tree actually stimulates root development, same as flexing the tree will help the trunk girth faster. Same same for 'petting' the tops of the foliage pads--it produces thicker foliage and more horizontal breaks.

Bob