Well, I can tell you mine is a wonderful plum, but it doesn't bear heavily.

I'd think Z8b would be pushing it for this plum anyway. That's awfully warm for a tree that was developed in Ithaca, NY.

If I were an Z 8b kind of guy, I'd be looking at Japanese plums and pluots. I know a lot of people think Pluots have pollination problems, but my 'Geo-pride' pluot was easily pollinated by the 'Shiro' plum and vice versa, until it finally froze to death.

Here in NY state it is mostly a dud although I have a couple of sites where it bears regularly and fully for reasons I've never understood. It's a fine tasting plum but in our conditions I'd recommend Castleton as a plum ripening at that time over Seneca.

Castleton is a smaller plum and therefore more affected by the skin. Both are prune plums and get up very high brix if left on the tree long enough but Castleton is the most reliable cropper of all the large number of E plum varieties I grow. It also bears younger than Seneca, has a more spreading form and is naturally semi-dwarf.

I've heard of the Seneca bearing well on the West coast, I believe, and there must be some reason Raintree carries it.

J and E plums are not interchangeable in my opinion and it's worth growing both if you have room and the climate for it.

I would keep it if I was you and graft on other varieties.

I live in Seattle - so while it doesn't really get too cold here it doesn't exactly get very warm either. My little Seneca Plum is a very pretty little tree. It has nice form, nice and open. I have room for only ONE plum. My neighbors have Italian plums so I have cross pollination covered for a European variety. We don't get enough heat for me to gamble with plum crosses or J Plums.

Since I have room for only one plum I may dig it up this next Feb/March. My dad has 5 acres north of me (8a) so I'll plant it up there and see how it does - we have room to play around there whereas with my own yard space is a premium.

Time to browse through raintree's plum list again. I like the looks of the gage plums, victoria, Reine de Mirabelle... oh choices

Definitely you have a pollination issue. 1st option is to graft a compatible plum onto it.. 2nd option put a compatible plum in a container close by. It will flower in container and will solve your issue :).

Seneca does require a pollination partner. If you have only room for one plum, then consider a self fertile variety like Italian or Stanley. But even they will bear heavier crops with cross pollination. Or consider a combo plum.

btw, the only thing the zone designation does is determine winter hardiness. It has no bearing on how hot it might be in summer and can be pretty much safely ignored for those purposes. European plums, including Seneca, Stanley, Italian, et al, can be grown in most parts of southern California, excluding te desert areas. In the PNW, it is a non-issue!!