Boug leaves dried after bare rooted repot in gritty mix...
I recently bare rooted and repotted a Bougainvillea from a bark/coir/perlite mix into Al's Gritty mix. The tree has caliper of about 3" and until recently had very nice, natural ramification and healthy foliage. No force or tools were used during the bare root, just water from a hose, but, despite my best efforts, most of the fine feeder roots were lost. Having never repotted a bougie I was surprised by how brittle the roots were - they just broke right off.
Droop was apparent within about 8 hours of repotting. All leaves were drooping within 36 hours. It has been one week since the repot and 3/4's of the leaves are completely desiccated; the remaining are curled and drying. Some branches show signs of failure at the tip (yellowing/desiccation) however most branches appear to still be alive.
After it was repotted I watered fairly heavily in the first 2 days and kept it in a lightly shaded area outside (daytime temps were 83F; night time 54F). When the wilting occurred I began to think, "weak root system + semi-arid loving tropical = overwatered" so I figured I'd let it fully dry for two days. The desiccation grew worse; I brought it indoors to keep a closer eye on it and better manage it's night time temperatures.
The tree is presently being grown indoors under a 400W Metal Halide. It's condition has steadily worsened. It is in a deeper pot (typical 13" green garden center type) on account of the long, thick and curling tap root. I have let it get quite dry between waterings but I have noticed that the top 2/3's dry about three times faster than the bottom 1/3 even though half of the bottom 1/3 is a drainage layer of 1" pumice.
Couple of questions:
Should I be waiting till it is dry all the way down or only until the first few inches are dry?
What are best watering practices for bougies in containers specifically and containerized trees in Al's gritty mix generally?
Also, any suggestions on how to handle a Bougainvillea in this condition?