Hi Dood. A lot of what you say is how I treat my tomato seedlings. I only deep water them at transplant, then they go a week or more without water to get the roots thirsty. When I water again, it isn't directly over the root-ball but further out ~8" from the main trunk held a berm or mote. Sometimes I don't go to all this trouble, but the times I have the plants have always grown larger and more healthy. I've pulled out grafted tomato vines at the end of the year with burred crowns and trunk that look like a baseball bat splintered out at both ends.
As for these Avocado trees, I had spread a small amount of Osmocote-Plus over the top of the container soil and root-ball (and beneath the mulch layer), but when I remixed 2 of 7 of the containers yesterday, I'm sure some of that got mixed into the general soil medium, which is unavoidable. I hope that's not the cause of the fizzled leaves.
I've left the mulch off these two trees, and I can do the same after I remix on the other five. It seems like for a well established, more mature tree, you should leave the mulch layer intact through the year, so as not to impact the surface feeder roots.
Something I've been thinking about with these 5-plants on the side of my house is drainage. The container soil should drain well, especially now with all the Perlite and DG. But when it gets to the bottom of the pot, it will hit 2-3 layers of weed barrier. The weed barrier is supposed to be water permeable, but I've noticed it drains through extremely slow. I'm thinking I might get a small diameter stake and poke some holes in the barrier to improve drainage. The down side of this is that roots from both the avocado trees (if any live) and the more established fruit trees four feet over in the neighbors yard could invade my pots. This has been a big problem in my yard as far as 30 feet out from the fence. I have blueberries in pots that have filed because of the roots shooting up from below into the small pot holes. I need to find a way to block these roots off in the long run, but it's not a task I'm looking forward to facing.
Thanks for all the tips. I'll keep the mulch off the young trees, perform the DG remix on the remainin 5, continue to leave them un-watered in the center, and then try and water around the pot boundary (possibly rough up the dirt around that area) to try and promote the roots. What do you think about removing any brown (seemingly rotting) roots I find on the sidewalls of the 5G pots (after removing the old soil mix)? Has anyone done this when planting out avocados, or is it better to leave the roots dead and alive to be, given root shock on the young Avocado trees is such a problem?