When California horticulturist Rudolph Boysen experimented with crossing blackberries, loganberries and raspberries in the 1920s, he created a berry that would eventually take his name. George Darrow of the USDA and Walter Knott, a California fruit grower, discovered and revived the abandoned plants of Mr. Boysen's farm, creating a viable specimen released for sale in 1935. The boysenberry's success sparked Knott's Berry Farm, near Buena Park, California, a popular amusement park. The boysenberry soon became a popular crop in Oregon and eventually reached New Zealand, which is now the world's largest producer of boysenberries.
Look for vigorous, woody cane growth with a profusion of thorns when searching for wild berries. Boysenberries, considered invasive in certain parts of the United States, grow in thick tangles when left to grow wild.
Look for foliage that is bluish-green in color, with smooth surfaces and serrated edges.
Identify small, white blossoms with an open arrangement of five petals surrounding a burst of stamen and pistils in the center in early spring. Boysenberry plants are self-pollinating, producing perfect flowers with both male and female parts.
Watch for fruit development when the blooms begin to fade. Boysenberries are considered aggregate fruits, consisting of numerous drupelets which surround a large central seed. In the early stages, boysenberries are light green in color.
Check canes for ripened boysenberries in mid summer, beginning in July in the United States. Ripened berries are large and somewhat cylindrical in shape, growing to 1 inch or more in length. The color of ripe boysenberries ranges from reddish-purple to nearly black.