I don’t know exactly what causes the extreme droopiness but the Florida Turpentine rootstock seems to exacerbate the issue. I hypothesize that the relatively fewer heat units and fewer daily light integral that we get compared to Southern Florida slows down the lignification of new wood.
Here in SoCal, we really only get about a 5 month growing season that in reality narrows down to 3 months of actual vigorous growth around June through August. Growth will occur before and after these three months but in our climate, you should time the last vegetative growth to harden before winter. You also want to wind down the total PPMs of residual fertilizer in the soil or pots so that you don’t get wayward blooms or vegetative growths out of season as the new growth is soft an highly susceptible to fungal and cold damage and can be an entry way into the rest of the plant.
If your mango tree becomes droopy, You Must Stake Up the Branches! Stake them up as soon as they are even a bit droopy because these will likely be your secondary or tertiary branching for future fruiting wood. The branches often get droopy after several aggressive vegetative flushes and almost always get droopy in winter due to the weight of the flower panicles. In either case, stake them up to how you want your branching structure when it becomes lignified.
In Winter when the droopiness is caused by the bloom panicle, remove about 2/3 of the bloom AFTER the blooms have fully formed unless under specific circumstances such as thinner wood that would otherwise snap if not removed earlier.
The reason you want to wait for full bloom formation prior to removal of 2/3 of bloom is because if you remove it too early, your tree will re bloom. Allow any fruit that sets to continue to expand and remove the blooms/fruit around this time of year or when average nightly lows are approximately 60F and above. In literature, it states an average of 62 but I find that averages of 60+ is usually sufficient to induce vegetative growth.
Addition of Silica May increase branch rigidity but allowing the branches to blow in the wind is also beneficial. I stated earlier to stake the branches as soon as you see it get droopy because I often forget to stake it up later. If you have a calendar or have good memory, you can allow your droopy branches to drool a bit and allow it to sway around in the wind to get the branching stronger and then you can stake it up at a later time but definitely before full hardening of the Branch.
Simon