Many trees, not just fruit trees will make a heavy fruit or seed crop one year and not so heavy or blank the following year. It takes a lot of energy to produce a crop that often the tree needs the next season off of fruit/seed production to recoup its reserves.
One of our spring chores is to thin the blossoms of the apples, they seem to be the main fruit we grow that benefits from this practice. Some varieties such as Gravenstein, Tydemans Early Red, Gingergold, Honeycrisp, Galas and others are particularly prone to biennial bearing.
Blossom thinning is a time intensive process and can be tedious and mind numbing after a few hours! But its also quite nice especially if its warm and the bees are buzzing and the sweet fragrance of apple blossoms fills the air. We mostly use our fingers to pluck the blossom cluster off, although sometimes we use our Felcos (hand pruners). My method is to consider each blossom cluster as a fruit, and thin the clusters about the same distance I would when I thin the small fruits in June, about six to eight inches apart. We can do the work by hand here because our place is small and apples aren’t the only thing we grow. Bigger conventional orchards use chemical thinners and organic growers generally use lime sulfur and fish oil during bloom. The idea is to kill off many, but not too many , blossoms to ensure a return bloom next year. Its tricky, you don’t want to do too good a job, because you never know what the rest of the spring will bring i.e a killing freeze ( this goes for hand and spray thinning).
We’ve had great success over the years with return bloom, even on notoriously difficult cultivars, but we do have a couple of varieties that don’t seem to respond to blossom thinning at all. Even though we also thin the fruit in June, the time is past when even heavy thinning then won’t bring a return bloom. It needs to be done in a timely manner just before to a week or two after full bloom.
before and after blossom thinning