Lee,

I would stick with the Japanese type of plums: Santa Rosa, Fortune, or Beauty for cross pollination.

Tony

Any guess as to whether a Stanley plum could cross fertilize this plum? Here's what the unripe fruit looks like.

Its not Superior. It could be Alderman. It will not be pollinated by any European plum, Jap and Euro have different chromosome numbers.

Scott

In Vermont you might want to use a Jap/American hybrid. Of course you don't want to get the same one you have. I would first take a fruit to the nursery you bought it from and see if they can identify it. This will narrow it down to what that specific nursery would have sold you.

I am leaning toward alderman because it is heart shaped.

Thanks all. I do think Alderman is the closest match. Does anyone know if a Stanley plum can cross fertilize an Alderman?

Otherwise, the cross pollinator plum that I had to cut down is growing back from the rootstock. I might just prune it into a bush and hope it will flower enough to pollinate the Alderman.

Stanley is a European plum, and does not pollinate any of the Japanese plums or the hybrid American - Japanese plums(like Alderman). I know that other hybrid plums like Superior or Kaga or Toka or a non-hybrid American plum are usually recommended for polllination; I think there is some cross pollination between the hybrids and the plain Japanese varieties if they bloom at the same time, but those are not hardy in the far north.
Not sure what your rootstock is, but that might work.

This plum in Superior, a Japanese plum. At least this is how my Superior plum looks--with the distinctive point at the bottom. My Superior plum is the first to bloom in the spring and is covered with blooms. I did not get plums until I planted another Japanese plum , Shiro in this case.

Can I assume that the rootstock variety would be a compatible cross pollinator for the Alderman, since the grafted tree was? Since the Stanley (which I planted as a replacement) is not compatible, I'm thinking to keep this rootstock growth pruned into a bush, just for pollination.

Hanna, the fruit on my tree is distinctly pointed at the tip, even when ripe. The pictures I see of Superior plums (which do look quite similar) seem to be more rounded at the bottom than the Alderman. Do you know any definitive way to differenciate a Superior from an Alderman (some leaf detail, bud shape, etc.)?

This is Superior:
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That is not Superior. Superior is very easy to recognize because the tree is very weeping... Also the fruit take on a very crazy purple hue when ripening. i'm also not sure if its Alderman... I have a tree full of Alderman right now and they are not pointed...they are more rounded at the end.

All kinds of hybrid plums out there:
link

While we may never know for sure what plum tree you have, wild american plums may be the best pollinator of all the japanese/american hybrids. According to professor Alderman of the university of Minnesota, all of the hybrid plums accept pollen from native plums. Specifically, Prunus Americana and Prunus Nigra.

Wow, I thought it would be simple to ID my tree based on ripe fruit, especially being so pointed at the tip. Frank's picture of Superior above looks a lot more like my fruit than other pictures I've seen of Superior. Not sure if you'd call this tree's growth 'weeping' although it tried to lean over a few years ago and needed bracing. The fruit is very sweet and delicious golden yellow.

I hope to photograph my loaded Superior tree and its fruit today and post it. My Superior tree is weeping in form as was mentioned by others. These plums are not yet ripe here in Michigan, but they're getting there.

I have tree identification problems of my own from wrongly labeled scions(apples)--but the investigation turns out to be interesting and fun.

I retract my "not Superior" from above, it doesn't look like my Superior but they seem to have different looks based on the climate. Mine never get anywhere near as red as the top photo. The way I recognize a Superior is when they are fully ripe they squirt juice all over you :-)

Scott

I cut my superior with a sharp knife or else they just make a huge mess...they are almost too juicy..

Here are pix of my Superior as grown in Michigan:

Hannah-

Are yours ripe? I've probably had about 20 that were ripe...

Maybe the plum above is Pipestone...

Hannah, that sure looks like my fruit, especially the pointed tip and the purple "blush" mentioned above. My tree's not as "weepy" as yours, though my fruit set is relatively light so less weight on the branches. Pipestone seems quite similar but lacking that distinctive pointed tip, as best I can tell from online photos.

I found a few that were ripe, and some have fallen to ground. But most are still trying to get there.

I'm harvesting delicious, juicy fruit. But most of the fruit is cracked. Anyone know why this happens?

Lee, a sudden change in moisture levels in the soil (and roots) is what usually produces cracking. This is usually from a dry period followed by a good rain.

Scott