Standard:
Grow up to 20+ feet tall
Plant 20-25 feet apart

Semi-Dwarf:
Grow 10-12 feet tall
Plant 12 – 15 feet apart

Dwarf:
Grow 8-10 feet tall
Plant 8-12 feet apart

Harvest:
Plums are green until just before ripening; then, the green gives ways to color. Japanese plums turn from green to red. European plums turn from green to blue. Pick European plums when they are soft and sweet. Pick Japanese and American plums when they are firm-ripe (when the flesh begins to give way to thumb pressure); let them finish ripening on the kitchen counter.

For More Information On Growing Plums, Check Out This Great Guide From Harvest To Table.
https://harvesttotable.com/how-to-plant-grow-prune-and-harvest-plums/