These are very helpful answers - thanks!

A 15-20' tall fig tree can have roots out 30-40' from the trunk, easily. So even a 5' tree would probably like to see a 50 or 100 gallon pot, realistically. So the choice between 10 and 20 gallon would be a no-brainer.

Honestly....I had forgot all about this thread.  Very helpful answers have been posted. 

There is no substitute for soil volume when it comes to containers.  Bigger is better...generally.  Roots growing from a tree planted in-ground have an infinitely-sized "container", after all.  Look at answer in posting # 27 that Jon provided.  This is an amazing statistic, and it's easy to see just how restrictive even large containers can be to the root system of a tree.

Nice to see some added information.


Frank

While it is true that a tree growing in the ground has a large root zone, it does not fully occupy it.  Also, some of the roots it produces are for anchoring.  In general, trees growing in a container have a much greater density of roots per area than those growing in the ground.  There are different set of compromises for growing in a container that is too small, just right and too large.  I would put trees in a container that I expected to be *just* too small for them in 2 years (about the time the growing mix needed to be replaced).  With the exception of the rooter cups, when my trees out grew their containers, I would bump them up to a container with about 3X the volume as the container they came out of.

Here is a guide from the University of Florida for container size based on the caliper of the trunk.

IMO, the bigger the container- the bigger plant and more fruit production. But, not going to follow that chart and plant my mature trees in 60-100g containers. It would be impossible to store them for the winter.

Navid.

Another way to look at this. What makes a bonsai a bonsai? Controlling the amount of soil, and thus the amount of roots. Yes they can live for hundreds of years, but they are stunted in their growth because of the restrictions imposed on them. Don't get me wrong, they are beautiful and fascinating, but it does illustrate the affects of an undersized container and rootball.

last year, i up pot my trees often during the summer. they did have heat stress due that, but they actually grow faster. this year, all my cuttings sat in 1 gal pot all summer long. they are growing well, but not as fast as the ones that i keep chainging the pots on.

Navid's post gave me an idea... sorry folks, I've had a bit of trouble sleeping so I am up thinking about goofy crap like this...

How much of the root system does a tree need to keep during dormancy? 

There has been much talk about partially burying a container to increase the amount of space for the tree to root, but not everyone has their containers set on/in soil.  Those who do allow their trees to root into the ground have the benefit of moving a smaller container when overwintering the tree.  Those who are growing on decks, driveways and even self-watering containers are at a bit of a disadvantage when moving the trees.  Unless they grow using a pot-in-pot method.  So here is the idea...

Plant the tree in a Superoot Airpot that is (depending on the size of the tree) between 1-2 gallons per 1" caliper, then nest the smaller container inside of a more appropriately sized container with the same growing mix.  I'm not positive about the SWC, but I think this should work.  Just before the tree starts preparing for dormancy, start exposing some of the roots in the larger container so they can die off before the tree comes in for the winter.  When the tree goes dormant, you only need to move the inner container inside.  In the spring, replant the smaller container in the larger one and repeat the process.

Any thoughts?