SIL has overgrown tree zone 7. I’ve seen conflicting advice about thinning plums. This seems like way too much fruit. We have already done a bunch of shaking the limbs.
It also grew very vigorously last year and we are wondering how much is safe to take off. I was planning to do some thinning by cutting off upright branches with fruit.
And also the large upright.
The tree doesn’t look especially overloaded to me- there are clusters of fruit it looks like and then long stretches without. Plums usually can get up their sugar if they aren’t a complete grape like traffic jam of fruit.
I would thin the smallest of touching plums or soon to be touching plums as they expand.
I wish my Green Gage had that load. -7F in Feb destroyed a lot of my plum crop.
