Apple trees belong to the Malus genus and are the most popular of any fruit tree, and it's not difficult to understand why. Juicy fruits, produced in abundance, even when the plants are very young. You can select an apple tree according to its fruit colour and flavour, but also according to its size. It all depends on the rootstock. Want an apple tree for a small garden? Choose roostock M27 (very dwarf), which will give you a tree that's only as tall as an average person. M9 is the next size up (dwarf), followed by M26 (semi-dwarf). Or train your tree up a fence in a fan, cordon or espalier shape.