OPPORTUNITIES FOR HIGH DENSITY PLANTINGS OF EUROPEAN PLUM AND SWEET CHERRY

Of the many rootstocks for European plums tested at East Malling only Pixy has dwarfed trees sufficiently to facilitate high density plantings. Although difficulties of propagating Pixy have now been largely solved its tendency to produce fruit of poor size remains a problem. Experiments examining effects on fruit size of tree spacing, flower or fruitlet thinning and irrigation are discussed. Colt rootstock is too vigorous to support fully intensive sweet cherry plantings without supplementary methods of growth restriction. New dwarfer rootstocks bred in Belgium, UK and West Germany hold promise for the future. Although not yet approved for grower use paclobutrazol has effectively dwarfed both plum and sweet cherry but its influence in advancing flowering time has increased incidence of frost damage to blossoms and reduced yields in some seasons.