Hello again and thanks once more for your generous advice!
Sadly, my clusias appear to be moving in the wrong direction, and this is after the heavy rains from last night.
Of the 14 I planted, most do appear to show signs of leaf growth. However, the five at the western end of the yard--or the end that yields the most unobstructed sunlight all day--show yellowing leaves, and three of those are now exhibiting signs of wilting; the main one in question is no better at all.
I deep-watered all of them today, and about an hour ago, I decided to dig up the very bad one. I saw right away that this one evidently did not pull out of the 15 gal container cleanly when it was planted, as it was just the primary root ball (about the size of a volleyball) with none of the smaller capillary roots attached. There is no question that the small root ball is getting soaked with water, but it looks to be a very limited root system. By contrast, all of the others have an extended root system in the funnel-like shape of the 15 gal container.
Oddly enough, the clusias that appear to be doing the best are the ones that are root-bound, where I can see the roots had circled around the inside of the container. Weird.
Do you have any advice at this juncture, or should I continue to deep-water regularly and accept the fact that I may lose two or three? Thank you...