Living Tribunal said:
So a few things. Ramification is indeed very easy with crepe myrtles but waiting for the first flush of growth to slightly lignify is paramount to decreasing leaf size. If you cut back, even to two leaves, on growth that's just a month old you will get shoots that are the same diameter and leaves just about the same size. They also grow so bloody fast that shoots on developed branches can overgrow rather fast.
However, I've also noticed that cutting too late on newly lignified wood is indeed a bit tougher to get predictable back budding from within that season. I wait until the first flush of growth has hints of brown and then chop it back depending on where I am with development of the tree. They also have a tendency to alternate buds when you left more than 3 series of leaves on the shoot.
Here are a few pictures of crepe myrtles I started development on this season, all were acquired and potted in March.
This is the first shoot of a siren red semi-dwarf crepe:
And then a few months after the lignification process began, notice the color of the initial shoot:
Here's a comparison in leaf size of an untouched shoot and the one above that's been cut:
Here's a dwarf pocomoke (ignore the perlite and the hidden nebari I luckily found haha):
Large leaves after the first flush (you can see them on the right branch):
And the difference in leaf size between a newly cut shoot vs an untouched one (notice the color in the shoot on the left):
And lastly a full size crepe:
Here's a bad cut (lignified now but was cut way too early, this is my play around tree for the season

):
And a good cut:
When developing crepe myrtles honestly the best way to go about them while developing initial branches/branch structure is to aim for 1 set of branches per year for the first 2-3 years then cutting all the way back after summer to get better taper.
Thanks again for this, I'd come here to re-read some things and realized I had only 'liked' instead of replying

I did take-on and, kind-of, learned from the "cut-too-soon" idea and think I've got that down (I just err on the side of letting things grow longer now, I figure at worst I'm wasting a little time
but at least it'll increase staggered-girths/taper in the branching!
Re the 'trial crepe' I'm glad I'm not the only one ROFL! I have a handful of specimen that I do things like that on, it's certainly a valuable learning-experience to be able to push things and see what happens!
Re my "flowering problem" on my two larger crapes, I removed the 2nd flowering-flush on both of them and, for whatever reason, one of them went for
a third (!) flowering push while the other went mostly-vegetative (literally 2 or 3 single flowers on the thing, am guessing they were buds I missed when removing the prior flush) So for the one that went back to vegetative, things are were great from right-after that 2nd flush's flowers were removed (this pic is like 1mo old now, it's just been vegging since

)
The other, my "cavernous crape" lol, has just been fighting me and is only now starting to give-up the fight, it'd just keep trying to push more flowers so I'd just actively remove flower-buds anytime they occurred and did nothing else (except normal husbandry) and through that I did get another good veg flush to the point I had that "branch-girth-disparity" to go for 1 last session for this season (gotta love FL ;D )

[wires were getting a bit tight!]
Sadly though, I can be a moron and
still will think "I know I'm in a rush right now
but I know I can be careful in wiring this!" and broke 2 branches while doing its last intervention of '18 (
BTW, I'd love your opinion on which side should be 'front' for this specimen, am pretty sure I know which is best in my eyes but want to be sure others see it! Here's both sides, right after the last works of '18:
And the other side:
[it's pretty obscured by the substrate, but in the last pic here ^, on the right-side trunking, where it slopes into the ground/nebari, that's actually a big fat surface root that goes almost to the side of the box, will be real nice when I can 'display' that

]
I use lots of guy-wires on my 2 crapes "to fight apical dominance"....I'm picturing the final canopy's shape and it just seems smartest to get many of the primaries into a more horizontal orientation, am figuring that filling-in the interior of the canopy will be pretty simple but that the bottom-spread of it kind of
has to be formed in this type of broad/spread manner to be the 'base'/structure for secondary/tertiary branching to fill-in the crown here!
-------------
These are my only 2 collected crapes, the rest are just cuttings that I don't really expect much out of as they're not dwarfs and I just started with ~1"+ thick branches, but have ~5 specimen I'm working like this guy:
Going to up-pot that today, had taken it out of its plastic cup (I use styro&plastic cups, 1oz and 8oz sized, for propagation...I propagate a lot

) and the root system was small-enough that I erred and figured it was a suitable size for the rest of the summer- this pic is weeks old now and the root-mat in there is so darn tight&dense that it's squeezing the substrate from the walls, like there's a 1mm-minimum gap between the entire perimeter of the substrate/root mass and the inside-lip of the container! Getting a re-pot next soon, probably today if I get to it (have ~10+ similar propagates that need up-potting, mostly bougies but a few more crapes too!)
Your dwarf pocomoke is just awesome!! Gotta say though, am a bit confused that you 'found' nebari- am guessing this was a nursery plant that you converted to bonsai? And what's wrong w/ perlite? Love the stuff! It's obviously not a great aesthetic but that's really only relevant, IMO, much further down "the development-road"! When still growing-out stuff, perlite is just such a great aggregate for many types of blends (IMO!), I probably use it at 15-20% minimum in pretty much any blend I make ;D