Apple trees come in all shapes and sizes. Choosing the apple variety is the fun part, but it’s just as important to consider the tree’s eventual height and spread. Some apple varieties naturally grow more vigorously than others, but the most significant factor influencing the mature height and vigour of the tree is the rootstock it has been grafted on to.
Apple trees sold in nurseries consist of two parts: the graft or scion of the apple variety and the rootstock. If allowed to grow on their own roots apple trees can reach heights of 15 to 20 feet – too tall for most gardens and orchards. To overcome this problem, apple varieties are propagated by taking a young shoot [the scion] from the selected variety and grafting it onto a small sapling of a related species – the rootstock. The main fruit tree then takes on the features of the rootstock such as a more compact habit.
Work on developing modern apple rootstocks was conducted by British scientists at the East Malling Research centre in Kent during the early 1900s. Rootstocks are clones of a mother rootstock that has been developed to have certain characteristics that influences a tree’s height, spread, disease resistance, or tolerance to certain soil types and weather conditions.
When buying an apple tree it is important to select a rootstock that is compatible with your site, soil conditions and available space. If a garden centre cannot tell you which rootstock the apple variety is grafted on to, find another garden centre.