Sweet Orange (Citrus sinensis) is a compact, evergreen tree, grown for its edible fruits. It can grow up to 9 m tall and 7.5 m wide and might tolerate some light frosts. It is probably the most popular of all citrus trees. The leaves are elliptical to oblong-ovate, up to 10 cm long, with narrowly-winged petioles. The flowers are white, sweetly scented, hermaphrodite - have both male and female organs and appear in clusters at the tips of the branches. The plant is self-fertile. The fruits are round or ovoid, orange to reddish-orange in color. The juicy flesh is orange and fairly acid and can contain few or many seeds.
If you live in a cold area you can grow sweet orange trees in a greenhouse or indoors, as they make excellent container plants because their size can be easily controlled with container size and selective pruning.
Sweet Orange trees grow well in a place with full sun or light shade or if grown indoors they will need very high lighting. They prefer a well-drained soil, moderately heavy loam with a generous amount of compost and sand added, with a pH between 5 and 6. Don't let the soil dry completely but make sure there is a very good drainage in the soil as they don't tolerate water logging.
When growing in pots, a compost mixture with equal quantities of loam and leaf-mould plus a little charcoal should suit well. When watering pot plants it is important to water only when the compost is almost dry, but do not allow it to become completely dry. Don't over-water. In the hot summer, the trees are watered daily in the greenhouse and fertilized weekly with a balanced fertilizer. During the winter, keep the plants moist and never let the nighttime temperature fall below 13 Celsius degrees (55 F).
The young growths in spring, even on mature plants, are frost-tender, so try to find them a place sheltered from the early morning sun. Plants dislike root disturbance so plant them into their permanent positions while young. If growing them in pots, take care when potting them on into larger containers. Since oranges bloom on new wood, any pruning should be done after the fruit ripens.
Sweet Orange trees can be propagated by seeds, by grafting selected cultivars, from cuttings of half-ripe wood in mid to late summer, in a frame or by layering in mid autumn. Seeds are best sown in a greenhouse as soon as they ripe, after thoroughly rinsing them. Sow stored seed in early spring in a greenhouse. Germination usually takes between 2 to 3 weeks at 13 Celsius degrees (55 F). When large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for at least three growing seasons before planting them outdoors. Plant them out in the summer and give them some protection from the cold for their first few winters outdoors.
