I live in Zone 5 in the Midwest and my European Plum has an abundance of fruit.
My sources say that Santa Rosa needs 300 hours of chilling, is partially self-fertile,
and is normally very productive. I have had a few seasons when my plum tree did
not do very much, and it was hard to determine the exact causes. The Santa Rosa
does do better with another one nearby, for pollination. Did you notice enough
bees around to pollinate the blossoms. I sometimes do hand pollination with a
Q-tip if I don't see any bees around. Hope your tree does better next year.

Sherwin D.

Dave Adams wrote:

We have a Santa Rosa plum tree in our backyard that has always given a bumper
crop of fat, juicy plums. This year, there's only like 3 on the whole tree.
I've done nothing different than usual regarding pruning, fertilizing, etc.

Anybody have similar problems, or even heard of it? What could cause this?

I'm in Marin county, CA

Thanks