Greengage Plum

Greengage plums have a very highly regarded reputation around the world. Said to originate in Iran, with history in the Middle East, Europe, Asia, Australia, and North America.

Greengages are somewhat small for plums, with very flavourful and sweet flesh that easily separates from the pit. They make for excellent dessert plums, but are also suited to an endless variety of uses – jams, compotes, crumbles, sauces, cocktails, chutney, and anything else your imagination can come up with (if you're really keen, look up the Portuguese recipe for Elvas candied plums).

There are several reasons they are not grown widely for commercial purposes: they can take up to seven years to bear fruit (grafting onto semi-dwarfing rootstock helps, as does branch training and other cultivation methods), and they tend towards biennial bearing (which just makes the years with bumper crops extra special!).

Pollination: Self-fertile, but will fruit even better with another European plum nearby.

Rootstock: Myrobalan 29C.

References:

Specialty Produce listing for Greengage plums.

What Makes Greengage Plums Unique, from Tasting Table. 

Article on plums from the University of Connecticut's Home and Garden Education Centre.