Luther Burbank’s Contributions to Walnuts

Luther Burbank began making controlled crosses between walnut species in 1875 after hearing about a “supposed natural European hybrid walnut.”  He made his first crosses using two American species, Juglans hindsii (Northern California Black Walnut) x J. nigra (Eastern Black Walnut),  producing ‘Royal’ walnut progeny that were fast growing, prolific nut producers that have been used as walnut rootstocks in the past.  The next year, he began making his first J. hindsii x J. regia crosses producing progeny that he named ‘Paradox’ because of the extremely fast growth and “in recognition of sundry other anomalies.”  Even today, seedling and clonally micropropagated ‘Paradox’ walnuts are widely used as rootstocks by the California walnut industry.  Wood from the Paradox ‘Burbank,’ reputed to be an original, was collected by Eugene Serr and Harold Forde in 1952 from the Burbank Garden at his home in Santa Rosa. It grows on the University of California campus and has been micropropagated and included in a current rootstock trial.  Luther Burbank also collected seeds from a J. regia growing in San Francisco because it produced regularly and very high quality nuts with relatively thin, but poorly sealed shells.  Shortly after he collected the nuts, the mother tree was destroyed by construction of a new street.  He selected one of its seedlings and introduced it as ‘Santa Rosa Soft-Shell.’  He described the cultivar as bearing large crops of nuts that are nearly white with thin shells and delicious white meat.  Burbank’s contributions to the walnut industry endure to this day.