Knowing about apple rootstocks, asking the nursery which rootstock a tree is grafted on, choosing the rootstock most compatible with your site, and following the best cultural practices for each rootstock will help the ecological gardener to ensure that his or her trees will be healthy and productive. Rootstocks are one of the unique aspects of apple growing. There is no other above-ground crop where so much attention has been devoted to roots! There are about 100 rootstocks for the major tree-fruits, and more than 20 for apple. Some of these rootstocks-like M.7 and M.9-can be traced back hundreds or thousands of years in history. In this bulletin we describe the relative strengths and weaknesses of apple rootstocks commonly available from fruit-tree nurseries. Apple varieties are propagated by taking vegetative buds from a young shoot (scion) of the desired variety (i.e. a ‘McIntosh, ’ ‘Jonagold’ or other named cultivars) and grafting those buds onto another tree branch or small sapling. This is necessary because the seeds of each apple are the result of pollination from a different apple tree species or variety. This makes each seedling a genetically unique individual with unpredictable traits; for example, seedlings sprouted from ‘Granny Smith’ apples might produce tiny red crab apples! Rootstocks are usually necessary for grafting and propagation of apple scion varieties. In past times, seedlings that sprouted naturally in pomace piles around cider mills were often dug up, and buds from known scion varieties were grafted onto these seedlings for planting new orchards. Since the genetic traits of these seedling rootstocks were unknown, their performance was unpredictable. Fruit trees in seedling rooted orchards were usually large, vigorous, slow coming into production, and many died off because their roots were not adapted to the particular soil or climate conditions in each orchard. To avoid these problems, most orchards today are propagated from “clonal” rootstocks-that is, they are grafted onto rootstocks that are genetically identical offshoots or clones of a mother rootstock type with certain desirable characteristics such as disease resistance, tolerance of winter cold, seasonal flooding and summer droughts, or reducing tree size. Clonal propagation ensures that the important traits of each rootstock will make the resulting orchard more manageable and productive. Most of the important apple rootstocks used today were derived from collections and selections by East Malling Research Station in England, during the early 1900s. Pomologists at East Malling collected and characterized the clonal rootstocks that had been developed by farmers during many centuries in Europe. They assigned numbers to each clone, and subsequent rootstocks have been developed by hybridizing these clones, or breeding them with other apple species and varieties. The following Malling or Malling-Merton hybrid rootstocks are important and widely available from nurseries: