Orange trees are evergreen and prefer a sub-tropical climate. They are capable of growing in greenhouses. In some locations they can be grown outdoors in the summer in containers and then be brought inside during the winter as long as they are afforded exposure to strong sunlight. How these citrus trees develop from seed to fruit-producing trees is the same regardless of where they are grown, provided their basic needs are met.
Most of today's commercially sold orange trees are hybrids grafted onto rootstock to produce specific varieties with engineered qualities. Seeds from these hybrids produce fruit but not like that of the parent. The fruit produced resembles an older variety that may not have all the same traits as the parent. Growing from seed requires that the seeds experience stratification or a period of cold equivalent to the length and temperature of winter in its natural environment. Once spring arrives, the warm temperatures and moisture loosen the seed coat, and germination takes place. The root and stem emerge, each traveling in the appropriate direction, and a seedling has begun.
Seedlings to Saplings
Like most trees, a seedling that receives proper care will grow about 4 feet tall the first year. During this time the tree must be well watered and kept weed free. Both of these conditions allow the roots to develop, which is important to the future health of the orange tree. Roots serve to anchor the tree and absorb water and nutrients. Leaves and branches also begin to develop, and the basic shape of the tree begins to form.
Flowers are necessary for fruit production because they kick off the reproductive cycle. Different varieties of oranges take different lengths of time to reach maturity. Growing conditions and climate also play a role, but most orange trees begin to produce flowers from 5-to-10 years of age. The flowers begin to form as buds in late winter and open in mid-spring. Orange trees have low pollen levels, so most are never pollinated and simply fall off. Once pollinated, however, the petals drop, and fruit production begins.
The quantity of fruit produced and the length of time it takes to reach harvest also vary greatly. Geography, variety and growing conditions contribute to the length of time it takes oranges to mature. Some pieces of fruit do so in as little as five months, while others can take as long as 18 months. In the beginning oranges are a dark green color, and they remain a shade of green until they are almost ripe. Then a transformation begins, and the fruit takes on its orange hue. Once orange, fruit remains on the tree for several more weeks to reach full ripeness.
Most orange trees live productive lives of about 25 years, producing 100 or more pieces of fruit each year. Well-cared-for trees can live as long as 50 years. They will continue to live and produce as long as nutritional and climatic conditions are conducive. Orange trees are sub-tropical and cannot handle temperatures below freezing for more than a few days. Exposure to prolonged cold ultimately shortens a tree's life span and productivity, and a few years of exposure could even kill the tree.