Sweet cherry rootstocks for the Pacific Northwest

All commercial sweet cherry trees are either budded or grafted. The part of the tree above the graft/bud union is known as the scion and the part below the graft/bud union is known as the rootstock. Sweet cherry scion cultivars have been selected over millennia for many reasons, but over the past century, breeding programs have concentrated mainly on achieving improved characteristics such as yield, taste, fruit size, fruit firmness, fruit color, precocity, and resistance to fruit cracking and disease. In contrast, rootstock cultivars have only recently received attention. Indeed, it is believed that ‘Mazzard’ seedlings were first used as sweet cherry rootstocks more than 2,400 years ago by early Greek and Roman horticulturists. The fact that ‘Mazzard’ continues to be used widely throughout the Pacific Northwest (PNW) is testimony to the success of this seedling variety as a rootstock. Over the past few decades, however, several new rootstocks have gained prominence, offering important attributes lacking in ‘Mazzard’. Many of these new semi-dwarfing rootstocks, although reducing tree vigor, may impart some disease resistance, induce precocity, and enable growers to harvest premium-quality fruit from high-density orchards. Furthermore, full production may now be achieved on these semi-dwarfing rootstocks within five or six years, compared to similar trees on ‘Mazzard’, which may take up to twelve years to reach full production. This publication presents the current level of understanding of the major cherry rootstocks and links it to their performance in the PNW.