I've been growing trees in small containers, but they almost always get planted in the ground after a year or two. Until recently I haven't really studied growing any trees in containers long term, and it looks like to do it I will have to mess with progressively repotting the trees as they grow until they reach their ultimate size, and then pulling them out and pruning the roots every couple of years.

While this is no big deal for a tree in a smaller pot, I'm looking at having to move and repot some big trees. What I would like to do is plant my lime and mango trees into very large pots, hook them up to the drip system (with fertilizer injector) in the greenhouse, and leave them there indefinitely, i.e. NEVER repot them. The greenhouse is crowded, some of the trees are already large and heavy, and I guess I'm just lazy.

Is there a container mix I can use that will not require me to repot the trees as frequently? Growing a tree in a really big pot doesn't seem all that different from growing it in a raised bed.

Over time your medium will break down and you will lose aeriation to the rootzone. Citrus in a container needs to be repotted.

Hi Clayton, I'm lazy too and am interested in the same if possible. I've been reading about bonsai media to see what inorganic options are available. I'm currently testing 3: LEKA, Turface, and diatomite...alone and as blends with biochar, peat moss, and/or potting soil. Way to early to know how any of these will work for me except to say that strait diatomite (NAPA Floor Dry #8822) killed my plant, while diatomite mixed with biochar did not. When the diatomite was wet out with water it had a faint petrochemical smell...maybe the char absorbed it? Anyway, I fired some diatomite in my woodstove and potted in that strait to see how it would go after volatilizing away the petrochemical...it didn't smell when wet out and so far the new citrus seedling is doing well.
Sorry I don't yet have anything solid for you to go on. Millet's experiments with cedar seem promising.

Cannot be done without the tree eventually gradually deteriorating. After your tree reaches the desired container size, the tree will from time to time have to be lifted and root pruned and the foliage cut back in proportion to the degree of root pruning. Then the tree can be reset back into the same container and the empty space filled with new medium. If this is not done, the tree will eventually stop growing and begin to deteriorate. - Millet

Millet, how often is this required?

In that case, I guess I'll just have to keep an eye on them, and repot them when they look like they're starting to go downhill. Hopefully that won't be for a couple of years.

I picked up 8 bags of cedar mulch today, and plan on filling the pots with a 2:1 cedar mulch and Pro-Mix (peat and vermiculite) mix.

While I agree with most of the sentiments in this thread, my father-in-law has a bearss lime that has been in the same pot for at least 15 years, probably longer. It is about 5 feet high, very healthy and produces around 30 limes per year. I am sure a regularly repotted tree would be more densely foliated and would likely be more productive, however keeping a tree in the same pot for long periods of time can be done. That being said, I would personally never do it.

More stable pot media can begin with fully composted organic materials, such as composted pine barks. These are harder to, and less rapidly degraded further than non composted which will 'compost' in the pot causing shrinkage and loss of structure
Biologically inert materials, sand, perlite, etc are useful for long term structure, and particularly the very fine component of the mix.
If the finest part of the mix is partly made of inert material, ie sand ( at least as coarse as brown sugar) there are less fine particles easily broken down.

I decided to go with 2 bags of cedar mulch and 1 bag of peat/vermiculite blend in a really big pot. You can see pictures here:

http://thebellhouse.weebly.com/1/post/2013/01/growing-mangos-in-big-containers.html

Time will tell how well this will work, but I would be willing to bet that I've got at least three years.

I think that is generally true of citrus planted in the ground, but when it comes to transplanting/repotting trees, you need to trim the foliage in relative proportion to the amount of roots that are damaged/trimmed.

For example, if while repotting a tree I trim the roots back approximately 10%, I should probably also trim back the foliage 10%. You don't want to create a situation where your tree is not only undergoing some transplant shock, but is also trying to support to many leaves with too few roots.

I'm sure someone more knowledgeable can elaborate.

My experience is not long enough but let me do some loud thinking:

Smaller chunks of root cuts should be better.
Let's define 100% root cut to be volume defined by pot (as outer circle) and inner circle with radius of a 1/3 ... 1/4th of pot radius.
Imagine that volume divided into 4..5 parts.
Assuming healthy tree, a 20..25% of root's cut in spring could make canopy cut unnecessary.
After a 4..5 years cycle repeats...

Mussing about optimal timing to do the cut:
Assuming that seasonal tree growth consists of cycles: a month of root growth following (or followed by) a month of canopy growth...
Which cycle (root or canopy) is the first one in season ?
I'm not sure but I tend to believe that tree starts with canopy growth based on inner reserves.
IF that is true then the optimal timing for root cut is just when that cycle ends (May for my location).
If everything is done properly roots will grow fast making canopy cut unnecessary.

My 2 cents only.

It always starts with root grow.
Getting the needed minerals and water, which lets the canopy grow them.
Growing as long as stuff is available and then again a cycle of root growing.

The canopy needs not to be cut, for that wait anyways till the root growing happened.
To cut the canopy and reduce the leaf surface and the reserves stored in the twigs and braches would only weaken the plant.

Let's learn from professionals :
Title : Citrus nurseries and planting techniques
container technology (garden of Luxemburg palace, Paris) described at the pages 171 and 172

http://books.google.sk/books?id=nYS3HESs1PYC&pg=PA171&lpg=PA171&dq=citrus+Poire+du+commandeur.&source=bl&ots=AV3cEJRGEP&sig=dykEsjJzQ2ym01PVfJ9VqRA9RXQ&hl=sk&sa=X&ei=7ZAOT_GuPIymsAa4wpVH&ved=0CFgQ6AEwBw#v=onepage&q=citrus%20Poire%20du%20commandeur.&f=false

Rad, thanks for the link.
Cultural practice shown there is for "orangerie box" i.e. a cubic shape whose side is 0.6 to 1.4 meter according to the age of the tree.

Above maybe fits what hydrobell wants but
that size is a way bigger than most of us have in our plans.
Our cultural practice, I think, should be more "bonsai" based.