Sour Cherry Production Map, Wikimedia Commons (AndrewMT). 

Sour cherries are grown in twenty-seven countries around the world, with the top percentage of production grown in Russia at 24%, Poland at 20% and Turkey at 12%. In the United States, the top producers of sour cherries include Michigan at 70%, Utah at 10% and Washington at 8%. Michigan produces the most sour cherries in the United States due to the climate influenced by Lake Michigan. Since Michigan sour cherries are planted on the eastern shore of Lake Michigan, the climate is most beneficial for sour cherry production from the effects that Lake Michigan has on winter and spring temperatures.

Sour cherries are harvested when the drupes are ripe, noted by a solid color content of red or dark purple. In order to insure future growth, sour cherries are shaken from the tree, so that the spurs (the short sub-twigs that produce the buds) are not removed with the drupe.