I have a theory that I’d like to toss out there. I have been planting apples and pears and hybrid plums and a multitude of other fruits each spring and fall since we moved here 9 years ago. Every spring for sure, there may have been one or two fall seasons that I did not add more trees. Being of all different varieties and different ages , ( recognizing of course that some rootstocks and some varieties are more precocious than others ), I have concluded as of this year when almost all of my trees regardless of age are suddenly blooming, that it has more to do with weather (for example last year was a drought), than it does the age of the tree. (Now, I did do a late fall, weak solution Boron spray to the bare trees last year also )…but I’m thinking flowering is mainly stimulated by the previous year’s weather…so those who are saying “i’ve had this apple tree or plum tree for so many years and it’s not blooming or not making fruit”…just a thought. I don’t fertilize my trees with nitrogen, aside from the duck and goose manure ( wood shavings, straw, and cardboard mulch that I put around them ( about 6 or 8 feet across) after they have been established a year or two. I do put a handful of bonemeal in when I plant them. Last year I tried 5 new apples, this year, if the chipmunks and racoons leave me any, I hope to try 10 or more new apples. So far, ( last year) just amazing flavour from Wickson crab, Trailman Crab, Ribston Pippin, …but also nice apples from Liberty and Novamac. Those first 3 are highly recommended if you like an apple packed with flavour.
Yes, bud set typically happens the year before for any tree or shrub that blooms or bears fruits on second year wood instead of the new growth of the current season.
Kind of funny…“I don’t fertilize my trees…”
“except duck and goose manure”!
In apples, flower buds are formed relatively early in the growing season before they bloom - maybe a month or so after petal fall. At this point, the plant has created next year’s buds, and a fraction of them are “induced” to transform from vegetative to flower buds. Induction is a complicated process, but the overall physiology of the tree, based on its age and maturity, and its energy/nutritional status all have some effect. This is why girdling and bark inversions have historically been used to bring full vigor (non dwarf) apples into early production. It’s part of the magic of dwarfing rootstocks. No doubt, anything that affects the energy and nutritional status of the tree could have an impact, including drought. But note that this cuts both ways - the way you get biannual bearing in apples is to have the trees energy status overloaded with fruit production so as to inhibit fruit bud induction for next year. On the other hand, prune a tree and fertilize it so as to cause overly vigorous growth, and you may equally trick it into thinking temporarily it’s a youngster again, and it will “forget” to induce flower bud formation.
Stone fruits are different from apples and different from one another, in the timing and to some degree the influences on flower bud induction. You can’t understand a plum by studying apples .