Plucking a fruit from an apple tree and taking a bite might leave you spitting out a bit of too sour or mealy apple. Not every apple tree that bears fruit produces crops for eating. The type of tree grown, growing conditions and climate will determine whether an apple tree bears edible fruit.
According to Washington State University, apple maggots render the fruit of trees they infest inedible. These native North American pests live out most of their life cycle inside the growing apple fruit. During the larval stage, apple maggots tunnel through the fruit which encourages bacterial growth to further erode the flesh. Once the apples fall off the tree, the maggots bury themselves in the ground to become pupae. Seven to 10 months later, the apple maggots emerge as fully grown adult apple flies which then mate and lay their eggs in the fruit of the apple tree above, continuing the cycle. Check with your local county extension office for the best pesticides to use to kill the maggots in your trees as recommendations depend on the variety of apple trees grown and the location.
The 4- to 6-inch wide fruits called hedge apples actually come from the osage orange. Native to Texas, Arkansas and Oklahoma, hedge apples grow from plantings across the Southern United States where landowners used these thorny bushes as natural fencing. Along with the thorns, Clemson University notes that hedge apples bear rock-hard fruits that contain an irritating, sticky juice.
Apples Grown From Seeds
Gardeners always purchase apple trees grown from grafts if they want to eat the fruit. Apples grown from seeds bear sour, inedible fruit without use outside of making hard cider. Johnny Appleseed scattered seeds across the United States to grow apple cider trees, not trees for eating apples.
European Crab Apples
Closely related to wild apples (malus sieversii), European crab apples (malus sylvestris) do not appear frequently and bear bitter fruits which have too tart of a flavor for consumption, according to Jake Fleming of the University of Wisconsin.