I used to get blossom on my plum tree when I had a crab apple next to it. I had to cut the crab apple down as it was leaning dangerously. Did not get any more plum blossom for 4 years until this year it is flowering again. Why is this?
No idea really.
Plum trees and crab apple trees are no more related than rose bushes and delphiniums.
Apophthegm - a big word for a small thought.
If you live in Derbyshire, as I do.