Cure for Pot Bound Trees

[dbonsaiw]

Fall is always a great time to find some great deals on nursery stock. And with nursery stock usually comes pot bound plants. I thought I'd share a "box cut" method I've been using.
My understanding is that once a root starts spinning around the pot there is really no way to straighten these roots - they will continue to grow round and round no matter if its planted in a giant pot or in the ground. In fact, Ive seen trees that have been up-potted and its root-bound nature cannot be seen because the root ball is still spinning around the trunk in the buried portion.
In my limited experience, I've found power washing, combing and other methods to simply not fix the problem.
The box cut method of curing pot bound plants is a take on an older method used by landscapers. When landscapers plant a root bound tree they will slice the root ball with a knife on four sides and also carve into the tap root. This doesn't really get rid of the spinning as much as it makes room for new, straight roots to grow.
With the box cut, the root ball is sawed on all sides removing all circling/girdling roots and the bottom of the root ball cut as well. The tree's roots are literally cut into a box shape. The roots can now grow straight.
I've done this to two maples so far and they seem to be doing great.
Now I need to figure out this whole "season" thing and determine whether I can chop some trunks on these guys come spring (or wait for roots to recover)

 

[leatherback]

I normally remove 80-90% of the roots so I am left with a flat rootball and no spinning roots. Off in a growflat and susans ready.

 

[leatherback]

example

 

[Tieball]

I cut off the roots using a cordless reciprocating saw and a landscape blade. Probably the same principle as you refer to as box-cut. I cut then as tight as I can, close to the trunk as desirable based on the tree, and smaller than the next container they move into. I do this in spring.

 

[Shibui]

Your Box cut sound like a pretty crude method. I agree it is of use for landscape plants because it does encourage new roots to grow outward and where visible rootage is not an issue.
For bonsai we usually work more methodically. Like @leatherback I frequently remove up to 90% of a deciduous root ball leaving only the roots which will be useful for creating future nebari.
Conifers need to retain more roots but fortunately many have more flexible roots, some of which can be untangled and rearranged where I want them.