All flowering plants use insects and other naturally occurring elements to transfer genetic material from one organism to another in reproduction. This process is called "pollination" and allows for genetic variation and survival for many plants across the plant. Orange trees are an example of this group and use several methods to ensure pollination.
Most citrus trees, including oranges, begin forming flower buds in early winter until spring. Since 99 percent of these flowers fall off without ever resulting in the formation of fruit, plants become largely dependent on temperature, moisture and adequate water. Since flowering and the creation of new leaves after winter uses a large amount of resources, trees must ensure a variety of possibilities for reproduction and not rely on just one.
It is possible for some orange trees, such as the Washington navel orange tree, to develop fruit without pollination occurring. When fruits develop without the use of either embryo or endosperm, the resulting fruits are produced without seeds. Since these fruits are seedless, they are unable to be used in reproduction for the organism. This is called parthenocarpy.
The most common method of pollination among orange trees is done through insects, quite often bees. Drawn to the sweet-smelling blossoms, the insects will enter the flower and unknowingly transfer pollen from one bloom or plant to another. Another method of pollination is done with the help of gusts of wind, which carry the pollen grains of the blooms between flowers.
Not all oranges can develop through ordinary pollination, when pollen is transfered between a single tree's blossoms. Allogamy occurs in certain varieties of orange trees, such as the Clementine mandarin trees, which need pollen to transfer between the blossoms of two fully developed trees. The flowers found on these plants tend to have taller stamens to better ensure the spread of pollen between organisms. Orange growers are unable to perform artificial pollination and rely heavily on insects to transfer pollen.
Pollination for citrus trees generally occur when the flowers begin to bloom. This is typically between the seasons of early winter throughout late spring. Once pollinated, it can take an orange tree anywhere from five to 18 months to produce viable fruit that is ready to be harvested. Most citrus fruit can be left on the tree for large periods of time after being fully grown without the danger of over-ripening.