Very large bramble fruit, usually considered, along with the loganberry and the youngberry, a variety of blackberry (Rubus ursinus). The dark, reddish-black fruit is especially valued for canning and preserving. It is grown chiefly in the southern and southwestern U.S. and on the Pacific Coast from southern California into Oregon. It was developed in the early 1920s by Rudolph Boysen (1895–1950) of Napa, Cal.
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In the late 1920s, George M. Darrow of the USDA began tracking down reports of a large, reddish-purple berry that had been grown on the northern California farm of a man named Rudolph Boysen. Darrow enlisted the help of Walter Knott, a Southern California farmer who was known as a berry expert. Knott hadn't heard of the new berry, but he agreed to help Darrow in his search for the berry.
Darrow and Knott learned that Boysen had abandoned his growing experiments several years earlier and sold his farm. Undaunted by this news, Darrow and Knott headed out to Boysen's old farm, on which they found several frail vines surviving in a field choked with weeds. They transplanted the vines to Knott's farm in Buena Park, California, where he nurtured them back to fruit-bearing health. Walter Knott was the first to commercially cultivate the berry in southern California. He began selling the berries at his farm stand in 1935 and soon noticed that people kept returning to buy the large tasty berries. When asked what they were called, Knott said, "Boysenberries," after their originator. His family's small restaurant and pie business eventually grew into Knott's Berry Farm. As the berry's popularity grew, Mrs. Knott began making preserves which ultimately made Knott's Berry Farm world famous.