When I started my business that includes managing very many non-commercial orchards in the S. NY region I had already immersed myself in all the literature I could find about growing fruit. I also introduced myself to a couple commercial fruit growers to get some guidance.
From the literature I didn’t learn what the growers told me, that no matter what you do, some years some varieties don’t set a good crop. What they didn’t tell me is why.
Over the years I’ve come to believe that crop load is only one factor in determining the following year’s crop. Even when thinning is done early, within 1-3 weeks of petal fall, there seems to be other factors in play with more than the most notorious biennial varieties. I now believe it is about every factor involved in storage of energy and may even go beyond storage levels in the previous spring- for example, that perhaps especially wet and cloudy weather beyond mid-spring can contribute to a lack of flower development for the following year.
Last year, almost the entire growing season was excessively wet and cloudy, and although I thinned all my apple trees well early and even mopped out vegetative shoots directly attached to the “trunk” of scaffolds to give spur leaves more sun, more than half my apple trees are practically barren this year. On another year following a good crop managed the same way the overall crop is usually much better.
I used to have purely biennial crops of Goldrush but started removing all the flowers from more than half the spurs before the end of bloom- they will have a decent crop this year, but there are few flower buds on the north side of both of my trees.
I gave the same treatment to Jonagold and it has a good show of flower buds this year, but Jonagold is a reliable cropper. So is Golden Delicious, which I gave no early flower removal to- it looks almost completely barren of flower buds this year as is the large Hoople graft on top of it. 4 other Hoople grafts that are now large branches on other trees are also barren.
In the orchards I manage that were not thinned early at all, I’m seeing a lot of trees without many flower buds. The exception tends to be big old apple trees on seedling root stocks in full sun Such trees seem capable of scaffold breaking heavy crops one year and still giving a good crop the following year.
Certainly dawn to dusk sun helps and most home orchards don’t quite have that.