Apple trees grow in the temperate regions of the world (areas that don't get too hot or too cold), generally in the latitudes between 30° to 60° north and south.  Apple trees are best adapted to places where the average winter temperature is near freezing for at least two months, though many varieties can withstand winter temperatures as low as -40°C (-40°F).

Apple trees are deciduous, which means their leaves fall off at the end of the growing season.

Apple trees belong to the Rosaceae (rose) family, and in the spring you can see the beautiful white flowers on an apple tree looking like tiny roses.  Taxonomists (scientists that name and classify living things) have called the cultivated species of apple tree Malus domestica, and the wild species Malus pumila.
 

Apples and pears are "pomes" because they have a paper-like core, a fleshy layer around the core (the inside part that you eat), and an outer skin.

The volume of a ripe apple is about 20% air (that's why they float), and 80% water.
 

SEED & FRUIT DEVELOPMENT

If you took a sweet, juicy, well-developed apple and cut it in half (cross-sectionally), you would see that the ovary has 5 compartments (called "carpels").  Each carpel should contain 2 seeds, for a total of 10 seeds per apple(except for the "Northern Spy" which contains 4 seeds per carpel and may therefore develop 20 seeds).

Apples that are well developed and have most of their seeds are said to be "set".  But, apples don't always set, and don't always produce the total number of seeds they are capable of producing.  Why?
 

GROWTH

Apple trees grow best on hilltops and on the sloping sides of hills because these areas provide good water drainage, and also allow colder, heavier air to fall to the valley below during frosty spring nights when cold air could damage the blossoms or young fruit.

Healthy apple trees produce "scions" (buds).  To produce new apple trees, farmers cut scions of a desired variety of apple, and insert them into the base of the stem or trunk of a seedling tree.  The seedling tree is called the "rootstock", and is a root or a root plus a stem.  This whole process is called "grafting".  The mature apple tree will then produce fruit of the same variety as those of the tree from which the scions were cut.  Farmers try to graft scions from apple trees that have popular and tasty varieties of fruit, with rootstocks that are robust and resistant to cold temperatures and pests.   Another method is to graft branches bearing full-sized fruit onto dwarf trees, and then grow the branches against a trellis.  This method allows a greater number of trees to be grown in an orchard.

In apple orchards, trees are planted in rows 3 to 9 meters (10 to 30 feet) apart.  This gives farmers enough room to pick the mature fruit, and also spray the crop if necessary.  Young apple trees must be carefully pruned during the first five years, so that the main branches are equally distributed up the trunk, and so that weak branches don't develop.   Apple trees may grow more than 12 meters (39 feet) in height.

An apple tree begins to bear fruit in 6 to 8 years, and is capable of producing fruit for as long as 100 years, though most commercially grown apple trees are replaced every 12 to 20 years.

PESTS

Humans are not the only species that love apples.  Many insects, as well as many microscopic bacteria and fungi, also enjoy the fruit--and sometimes the whole tree!

One particular insect that may damage growing apples is the "Codling Moth".  In the spring, this moth lays its eggs on the fruit and leaves of apple trees.  "Larvae" (caterpillars) hatch from the eggs and eat their way into the young apples.

The "European Red Mite" is an insect which damages the leaves of apple trees.  In the fall, female European Red Mites lay their eggs on the bark of the tree, and the young mites hatch in the spring just before the flowers begin to bloom.  The young mites damage and weaken the tree by sucking sap out of its leaves.

The "Apple Maggot" is another insect that can harm an apple tree by eating the fruit.

Some species that can harm apple trees are microscopic in size, but attack a tree by the billions.  "Fire Blight", for example, is a disease caused by a bacteria which kills twigs, leaves, and blossoms.  It gets its name because a tree infected with the disease develops a burned appearance.

In the wild, nature has its own ways of preventing certain species from becoming overpopulated.  Farmers, however, often need to use powerful "pesticides" (pest-killing chemicals) to control insects and microscopic organisms.  The problem with pesticides is that they sometimes have negative side effects.  For example, an "insecticide" (a pesticide used to kill insects) sometimes kills all the insects on a tree, whether they are harming the tree or helping it.  Pesticides have also been known to wash into local waterways, where they may poison aquatic life.  As well, some pesticides remain in or on the fruit, which are then consumed by humans.  Some farmers even spray chemicals onto apple trees to prevent the ripened fruit from dropping before it can be picked!
 

Some less toxic ways of controlling insects and micro-organisms are by pruning infected wood, breeding apple trees which are pest-resistant, or introducing into the orchard animals or plants that have pest-fighting abilities.

HARVEST & STORAGE

Apples are picked by hand, and a healthy apple tree can produce about 380 kilograms (840 pounds) of fruit each year.  Apples that ripen during late summer generally do not store very well.  However, varieties that ripen in late autumn can remain fresh for up to a year if they are stored in cold, humid rooms.