Many fruit trees are grafted on to a specific root system, or rootstock, that determine the size to which they will grow. These range from dwarfing rootstocks, ideal for small or medium-sized gardens, to those that produce a huge mature tree.
When buying a fruit tree, the label or product information should give details about the rootstock it is grafted on to. Grafting unites two plants so they work as one. The rootstock determines the tree's vigour and height, while the scion (the top part of the plant) determines the variety, and hence the characteristics of the fruits.