A mislabeled tree from St Lawrence nursery, not ‘Northern Blue’. My most productive tree this year.
Mid season ripening, just before Toka, after Underwood. Dwarfy weeping growth habit. Semi freestone, productive, precosious. Skin is sour and astringent, making me think it must have p americana in it. Flesh is sweet, not super juicy like some, and slightly coarse in texture.
Any ideas what it might be?
I have a plum almost exactly like that…it’s a seedling from my Alderman. Too me the tree is a wild plum//what i think is the thickets of wild plums near my house were pollinating my Alderman…These fruit on my tree are actually very good…very sweet and the skin isn’t astringent/bitter. The birds leave them alone too… what’s not to love 
I just took these pics today.
Of the plums I have grown, La Crescent sounds like the only potential match.
I have LaCrescent, that is not it. My LaCrescent is a much more vigorous tree, fruit are more rounded and smaller. This unknown’s fruit share some similarity with South Dakota, which ripens later. Maybe it is another ‘improved’ p americana hardy pollinator, like SD.
It is a grafted tree, not a seedling, so I figure it must be something!
I see…maybe some type of cherry plum?
I’ve picked wild plums before out in the woods and while the flesh is sweet, the skin is usually astringent…you almost have to spit out the skin. My seedling.the skin is fine…so its not pure prunus americana…
I looked at their 2014 and 2015 catalogs and thought that it might be Percy’s. One of my
books (Plums of North America) has a match for the skin and flesh color with an Aug. ripening date but it says that Percy’s is a clingstone.
Percy’s sounds like a possible match…thanks for the sleuthing!
My trusty pickin’ partner and I harvested the bulk of the fruit from my unknown (Percy’s?) plum tree. Most will be combined with some wild bluebs, crabapples, elderberries for our ever changing Hedge Preserves.
Tested a few with my refractometer- between 15-18 brix.
They are pretty fruit.
