Oranges ripen on the tree. Unlike some other fruits, such as avocados, an orange won't continue to ripen after harvesting. Therefore, orange growers attempt to pick their oranges when fully mature and before the fruit becomes overripe. Home orchard growers often judge ripeness by the colour and size of the fruit. It is sometimes difficult to use colour as a judge, as changes in air and soil temperatures can alter an orange's colour, without regard to the actual ripeness of the fruit.
Gardeners who add an orange tree to their garden typically plant a young tree from the nursery, as opposed to planting from seeds. When properly planted, it will take the young tree about three years to begin producing fruit for harvest.
When an orange tree begins producing fruit, it typically goes through a "juvenile" period, which lasts about two to seven years. During this time, the tree might be thornier than normal and produce few oranges. The fruit might be large and coarse peeled.
Orange trees normally bloom in the spring, producing more flowers than the fruit it produces for that season. During late spring and early summer, the orange trees begin dropping small underdeveloped fruit, or "fruitlets." Orange growers sometimes refer to this as the "June drop."
The length of time for an orange to grow on a fully developed tree depends on the type of orange tree. Depending on the variety, a navel orange might take 7 to 12 months to mature after the fruit sets. It takes 12 to 15 months for the Valencia orange to mature after the fruit sets. A Valencia tree is capable of carrying two crops at the same time. This means the tree will have two sets of orange on the tree at one time. This requires two separate harvests for the tree.
Depending on the region, navel oranges mature in winter and early spring. During its third season, the navel orange tree might produce about 4.54 to 6.8kg. of fruit, yet produce 100 to 150lbs. when fully mature in its 10th season. For Valencia oranges, the fruit matures in the late spring and might remain on the tree for the summer. When left on the tree after becoming ripe, the orange peels often turn a bit greenish. When picking oranges, at least 25 per cent of the peel should be yellow-orange in colour.