I have a 9 year old Italian prune plum tree located in Seattle. The tree is very vigorous but it doesn't really bear much fruits every year. It flowered crazily just a few weeks ago but now I noticed most of the flowers or fruitlets have started to drop! Last year I have less than 50 on the tree..I think I'll have another year of small production. So in order to increase the yield, I'm thinking of getting another plum tree for the pollination purposes. However I did not see any present of bees(yes, not even one) around the italian plum tree while it was in full bloom a few weeks ago. So my question is if I get another plum tree let say "Victory" or "President" plum, would theyreally cross pollinate each other at all w/o any present of any bees? Maybe the wind or hidden insects that I didn't see can cross pollinate them? How far apart should I grow them in order to increase the successful rate of cross pollination?
Also, are they any fertilizers that can be used to increase the fruiting reliability? I'm thinking maybe the fruit is missing something but the tree seems to be growing very strongly.
I appreciate any replies. Thanks!