Apple rootstocks have traditionally been divided into three groups: standard, semi-dwarf, and dwarf.
A standard size tree refers to trees growing on seedling rootstock. If trees on seedling rootstocks are not pruned to limit tree size, the trees will reach a height of about 30 feet and have a crown diameter of about 30 feet. Orchards planted before the 1960s often had only 40 trees per acre and were spaced 40 feet by 40 feet. With good pruning, standard size trees can be planted at about 26 feet x 20 feet with 84 trees per acre; these trees will attain a height of about 24 feet.
Semi-dwarfing rootstocks typically produce trees that are about 60% to 90% of standard size, with a height of about 14 feet to 22 feet, depending on the rootstock. Semi-dwarfing rootstocks were commonly planted at a spacing of 22 feet x 16 feet (132 trees per acre) during the 1960s through the 1980s.
Dwarfing rootstocks typically produce trees that are about 30% to 60% of the size of trees on seedling rootstocks, with a mature height of about 6 feet to 12 feet. Depending on the soil, scion cultivar, and training system, trees on dwarf rootstocks can be spaced at 20 feet x 14 feet (173 trees per acre ) to 14 feet x 4 feet (778 trees per acre). Some of the more progressive apple growers, in regions with less vigorous growing conditions, are planting very high tree densities with spacings of 14 feet x 2 feet with 1,556 trees per acre.
|Effect of rootstock on tree size and vigor. Tree size as percent of seedling.|
|Image used by permission. © State of NSW through Industry & Investment NSW (2011)|
Dr. Emily E. Hoover, University of Minnesota
Dr. Richard Marini, Penn State University