You'll find some very, very helpful information in these two threads from the container forum:

Container Soils - Water Movement and Retention XVIII

Fertilizering Containerized Plants IV

Although they discuss containerized plants in general (rather than just fruits), most if not all of the information is applicable to growing fruits in pots.

As to some of your specific questions...

"My question is once they start growing big are the nutrients in the pot soil is sufficient for the plants?"

No. Given the tight confines of pots and the limited soil volume, microbe activity, etc. you absolutely need to provide supplemental fertilization. In my experience, you'll get more reliable results with a synthetic fertilizer, but that's another discussion entirely.

"I can change the soil, but am I not going to disturb the roots?"

Disturbing the roots isn't necessarily a bad thing. In fact, as you'll see in the linked threads above, periodically disturbing the roots (root pruning, etc.) will enhance the vitality of your plants.

Yes...you have to fertilize. I grow a ton of trees in pots. Yes...you do need big pots if you want fruit. I like nursery pots, the bigger the better (the size of the pot will determine the size of the tree...root restriction). I don't bother much with perfect soil (trees in my opinion will grow in just about anything, given nutrients/water). You will have to water...often...in hot weather...like every day. I do try to use a light soil, so the pot doesn't become impossible to move.

These are just a few of my trees (yes..there are more!)...
{{gwi:61918}}

The only thing I'd disagree with is you don't need big pots. I've grown almost all fruits in 5-12 gallon pots. In Frank size pots, 30 gal, I've fruited 4 trees.

Here's 3 nectarine fruiting in a 12 gallon pot. About 6-10 good size, high brix fruit per tree.

{{gwi:61919}}

This post was edited by fruitnut on Fri, Feb 7, 14 at 13:14

you are all amazing...

I want to be a pro like you.

Fruit-

30 is too big. I think the #15s (black plastic) are perfect. The big ones are just too heavy/bulky. I'm actually going to get rid of them soon (this spring). My small pots (#7s) just dry out so fast. I do think growing in pots allows a person so much freedom from pests/weather/early fruiting/zone denail (using a greenhouse).

I actually brought my Flavor King pluot inside today (the pot is frozen...lke a big ice chunk)...it'll go in the basement for a few days (low 50s) and then i'll bring it upstairs (around 68F) to start to bud out...hopefully by the time it flowers i'll move it outside under plastic...

Frank:

Your plastic pots pictured are about right. The half whiskey barrels must be 25 gallon or so? Agree that's too big for most unless very strong or have carts and concrete. Repotting that size takes a very strong back.

Using a light weight mix really helps. To me that means something like pine bark for majority of the mix.

Pots do have a real advantage for season extension and flexibility. Even with a greenhouse pots allow one to only grow fruiting plants in the best spots. The first year or two can be spent in less valuable growing space. And if something doesn't work out it can be immediately replaced with another fruiting tree.

But pots are more work: watering every day and repotting. Fruit quality is more variable and smaller.

I've gone to all inground where possible. Easier and less work. I can water once every 10 days via drip and actually be gone once in a while, or often if wanted.