While reading Jason's thread on up-potting, James made a point abut the root mass being inefficient because of the tightness of the root mass (my wording).  I think this is a crucial point to the discussion and would add that a root that does not touch soil/dirt/mix, etc is somewhat, a wasted root, in that it can only take in moisture and does not contribute nutrition.  A plant puts out more root surface by adding root surface, length, girth, new roots, so the roots can add to the process of water/nutrition intake.  All that would be fine if you were doing hydro/aqua ponics of some sort, which most of are not doing.

To the point, I would like to solicit input on root pruning, I know not what I speak of on this (or others, LOL) subject.

I agree, Jason's thread should be a sticky.  OBTW-this is what this forum is all about, IMO.

i thought the whole point of root pruning was to promote new root growth since the space in the pot is limited and it will get filled with roots. i only had to do an emergency root pruning so far in past spring. i took a wedge of root out of the root ball and that was it.

i'll be doing more extensive one this winter where i'll be removing 1/4 of the root ball along with about 1/4 of the top.

I read some time ago that the most effective way to root prune is to:
-Wait for the tree to be dormant
-Let it dry
-Pull it out of the pot
-Cut the round root ball into a square
-Re-pot
-The next time you will repeat this operation, cut at the corners of the square (now a cylinder again). This is a way to rejuvenate the root system.
You will be stimulating a lot of new roots, especially capillary ones which are responsible for water and nutrients uptake. It also seems simpler than cutting in a circle.

Fig tree bare rooting and root pruning IMO should be performed at least every few years due to their aggressive growth. Its often mentioned, but not usually discussed. I've observed that a lot of the stagnant growth and leaf deformation that has been attributed to FMD can actually be traced to problems with the plant roots, either it is root bound and or not absorbing enough nutrients to maintain healthy plant growth (nutrient deficiency). Note bare rooting and root pruning are actually two different procedures. Bare rooting establishes the scaffold (main) root structure, root pruning removes the apical tips.

Nutrient uptake occurs at the small root hairs, root pruning the root ends removes apical dominance and allows branching. Root pruning is very similar to branch pruning, we prune the main branches (scaffold branches) to induce fruiting branches, leaves and leaf node for increased fruit production, by removing the apical tips. The roots have to thought of in the same way, pruning away the apical tips allows the main scaffold roots to grow side roots (branch roots) that produce smaller "hair roots". Its relatively easy to used a hose and water to wash away the potting mix and untangle the root ball (bare rooting), easing the pruning and re potting procedure. Up potting is not always necessary when root pruning is performed regularly. I have for years followed the accepted advice when re potting or planting in ground, to "place vertical cuts in the side of the root ball, to stop circling roots". If you bare root this plant at the end of that growing season, many times you will notice that you have created a smaller (original) root ball with radiating new growth, many times the original root ball is extremely dense and void of any root hairs, it may be girdling itself and is not contributing to plant growth or nutrient up take, bare rooting avoids this problem. Bare rooting can be visualized as maintaining a root main scaffold (main root branches).

IMO bare rooting containerized plants should be performed at least every few years and root pruning should be performed yearly at the start of the growing season.

Good info.  Thank you Pete.

The fundamental reason to root prune is to maintain and maximize the efficiency of the root system of the tree while minimizing the problems that growing in containers presents. 

As the roots grow, they change from feeder roots (thin roots) to anchoring roots (thick, woody roots).  As they become thicker, their efficiency in taking up moisture/nutrients begins to wane.  Anchor roots are great for trees grown in the ground.  The last thing any (most) of us want is to see our large fig trees blowing down the road during a wind storm because the roots did not hold it in place.  In containers, however, the anchoring roots become less necessary and even counter productive.  Given that most growing mixes occupy about 50% of the volume of the container, and the water we put in occupies part of the remainder, there is a great benefit to removing less efficient roots thereby allowing more room for the more efficient (feeder) roots to occupy.  Root-pruning containers seem to do a decent job of accomplishing a dense, fibrous root-mass.

Root pruning can be accomplished in many different ways.  There are, however, benefits to periodic bare-rooting of container grown trees.  When a tree is freshly potted, it is occupied something like 50% growing mix / 25% air and water / 25% roots.  Over time, the roots of the tree grow and the components of the growing mix decay and the ratio changes (I'm making up numbers for illustrative purposes only) and it may look something like 30% / 15% / 55% and the tree is still grows in a healthy manner.  Given enough time, though, the ratio becomes more critical... getting to a point where the roots and remaining growing mix occupy 100% of the container.  The growing mix has decomposed and compressed so much when the tree is watered, the water runs down the side of the container and out of the drain holes.  Even at this stage, the roots do not stop growing.  As the root mass compresses, the roots will be girdled.  Simply moving the tree into a larger container does not alleviate the compression.  Period bare-rooting eliminates the compression and keeps the growing mix fresh (particle size is important).  It also allows the grower to identify and correct problems. 

In 2006 I bought a ~6' tall Black Mission fig tree in a 3 gallon pot from a nursery in NJ (it is one of the trees in the car behind me in my avatar picture).  The tree was long overdue for root work and barely held water.  Before I did root work on it, I took a chopstick and drove it into the top of root ball as hard as I could.  The chopstick did not go in more than 1/4".  It took me more than 3 hours to bare root the tree and it was evident when I got to where the side of the one gallon container and the rooter container were and each one was more difficult to work through.  This is not the only tree I've received with this type of compression. This past year, I bought some trees from a nursery.  One in particular I noticed small particles of growing mix washing out through the drain holes when I watered it.  When I pulled the tree from the container, the bottom 60%+ was nothing but roots.

Here is my method for bare-rooting and root-pruning a tree which I have not done root work on before:  I water the tree about 24 hours before I start.  Once I remove the tree from the container, I use chopsticks to start removing the growing mix and comb out the roots from the bottom up.  Once I get through the bottom inch or so, I start raking the outside of the root ball.  Once I can get the roots pulled away, I work (along with a little shaking) the growing mix out of the root ball.  In general, I work from the bottom up.  Once all of the growing mix is off, I cut the roots to 1/3 to 1/5 the radius of the container the tree is going into.  Then I remove a few (it's a judgement call but probably about 20%) of the ticker roots from the base.  Then into the container with new growing mix... water in and stake.  Here is a before and after on root pruning of an LSU Purple: