I have one scaffold of Flavor Supreme on a multi-grafted Spring Satin tree (Myro rootstock). The other scaffolds are: SS, Lavinia and Weeping Santa Rosa (WSR removed last summer). The tree is moderately vigorous, certainly less vigorous than many of my other pluots/plums. The tree gets dawn to dusk sun, and Lavinia/SS both produce very well. As usual, the FS scaffold produced a half dozen fruits for me every year, except this year it produced about 18 fruits, despite the fact that about 50% of its wood didn’t produce any flowers (winter bud kill). I have long contended that FS low production is not a pollination issue, as me and others tried hand pollination with no success, and I also see a lot of wild bees working it during bloom.
I have read/heard that some farmers spray their cots with boron around bloom time to improve fruit set. So, I tried that last year, but unfortunately it didn’t make a difference. This year I decided to spray a different nutrient essential for fruit development, which is potassium. I sprayed it at petal fall and two weeks later (both FS and Candy Heart Pluerry, which is another scant fruit setter, though not as bad as FS). The result was 18 fruits on FS and loaded branches on CHP.
Now, I know this is a single data point on a couple of scaffolds, so scientifically I can’t make any solid conclusions, yet this is what I would call a “lead”, that’s worth further experimentation. So, whoever has a FS (or other plum/pluot) that does not set well, I invite you to try potassium spraying with me in the coming seasons to see if this will turn out to be a true finding or a one time fluke. Next season I intend to spray potassium just before bloom, at petal fall and two weeks later. Below is the product I used, and I used 0.5 tsp/gal.
