This scenario appears all too similar to my own stubborn-to-bloom brugmansia issues from the past, and only with extensive trial-and-error experimentation was I finally able to hone in on what I believe to be the sources of the plant cycle's retardation of bloom branching/inducing.

For starters: Noticing what you've mentioned as being located in Georgia (I am in Central Mississippi), I am going to go on the assumption that our climate zones/growing conditions are very similar, if not just about nearly identical. (I'm in very thickly humid, swampy Zone 8A, but not far from straddling the line between 8A/8B, especially given the most recent years of drastic climate change.) Secondly, judging by the photo above, I am to assume that you are growing them in a permanent spot in the ground, correct? Meaning - that even with winter dieback, you await for the reemergent growth of new shoots to return from the root base, upon each subsequent Spring, correct? Lastly, if your South-Eastern/Gulf State soil type is anything like mine, it would be heavy, sticky, soppy clay. Yes? Thus, if you can nod to all three of these parameters as matching my own, then what I can recommend for you is that you dig up your root balls, greatly enlarge the planting holes (by no less than *5* times as wide and deep as the root mass/balls of the plants), hand-mix a medium which is 1/2 compost with well-aged manure and 1/2 "Soil Conditioner" (ex: Those very big yet thankfully very cheap bags sold at Lowe's, under the 'Evergeen' brand, which is composed of finely-ground pine bark and other forest detritus). Use jumbo plastic buckets to hand-sort that half/half blend in bulk to make your life a lot easier.

Why that recommended hand-made mix, speficially? Well, the kind of soppy and sticky clay soil which I previously had my brugmansias sitting in would do more than just raise the risk of root rot. It would very specifically inhibit the transference of key micronutrients (especially magnesium and iron), reduce the efficacy of nitrogen in the soil, as well as lack in full-spectrum bacteria/microorgamism biodiversity that promotes optimal growth of the bloom-division stages later in the season (towards mid to late Summer). In other words, the kind of soppy and sticky clay in my region acts as a blocker of this later-stage developmental uptake. As a result, we get a lot of tall, singular, and otherwise healthy-looking spikes on the brugmansias (and they certainly stay more than well-watered because of the surrounding clay) ... but ... this seems to stunt the branching off of those characteristic Y's" from where the flower buds tend to form. Therefore, the hand-sorted mix that I propose has appeared to resolve this issue, at least for me. Sure, we can go the easier, lazier route and just add some extra nitrogen as well as sprinkle added magnesium sulfate and iron sulfate into our fertilizer, but it's just going to get mostly "locked up" within pockets of that sticky, goopy clay and not evenly diffuse far beyond the immediate root mass. So again, I recommend a complete overhaul by excavating and altering the entire composition of the soil surrounding the brugmansias, and it has to be a very, VERY deep and widely spacious ammendment zone, at that. To be sure: Be more than overcompensating with digging out that clay. As if you are planting a very large tree. I've excavated *FOUR* full wheelbarrows worth of clay for planting six side-by-side brugmansias, to give you a good visual of just how zealous I have been. But it is well worth it for me, because the roots have copious amounts of breathing space in all directions, microorganisms (bacteria, fungi, etc) can spread far and wide to metabolize all soil-borne substrates, and all micronutrients as well as your fertilizer feedings will diffuse evenly.

The lesson I've learned is that proper soil respiration, microorganism colonization, and micronutrient diffusion is not to be underestinated in how integral it is for promoting latter-stage shoot branching/Y formation/bud development.

Take cuttings from above the "Y" and plant it in the spring, youl have blooms months sooner as your now growing an entire plant which is "bloomable" since above "Y" when rooted.

This is the trick we breeders use, it also creates a smaller more bushy plant. I say smaller in relative terms as you still can have a large plant grow but should be bustier and more dense with many more branches starting lower closer to soil and above. The plant doesn't know the difference it will start your blooming season way easier since your not waiting all summer for the plant to mature and branch and bloom. I have a rooted cutting of Maya taken above the "Y" and it's been just 2 months since cuttings taken, they have rooted, foliage great, and already has buds forming. These root very easily as long as you can root the more woody cuttings, green soft cuttings will more likely rot. Thumb thick ideal however taking cuttings above the "y" makes more difficult to obtain hard wood cuttings. Rooting a cutting from just bow a "y" will give same results as long as you let everything grow from above the "y". Anything below will be taller,straighter stems like you have now, which will take longer to bloom. However may give you more flushes of blooms later in season 😉 since will "y" later at the top of those longer stems. Hope.makes sense. Cheers!!