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Growing Sweet Oranges: Citrus sinensis

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Overview
A member of the Rue family. Modern citrus fruits, according to genetic analysis, are complex hybrids arising from mandarin, pummelo, citron and pepeda ancestors, refined by more than four thousand years of cultivation. Citrus sinensis, the sweet orange, has hundreds of cultivars, classified into four groups: Mediterranean, Spanish, Blood, and Naval.

Description
Form: Tree.
Lifespan: 50-100 years.
Leaf retention: Evergreen.
Growth rate: Slow to moderate, depending on rootstock.
Mature Size: 30' high, depending on rootstock. Width varies with cultivar.
Flowers: White, five petals, fragrant.
Bloom: Late winter into early spring.
Self-fruitful: Yes.
Years before fruiting: 5-6 years from seed, less on some rootstocks.
Fruit: Round to oval, ripens to yellow or orange. Flesh is juicy and sweet, yellow, orange or red in color, divided into 10-14 segments. The skin is tight and difficult to peel. Seedless cultivars are available. Sweetness depends on total amount of sunlight, nothing else.
Months for fruit to ripen: 9-12. Color is not a reliable indicator of ripeness. Remove one from the tree and taste it to determine if fruit are ready for harvest. Fruit that have dropped from the tree within the last 24 hours are ripe and safe to use if they have no cuts and smell citrus-like and not moldy. Most Naval Oranges ripen in winter or early spring. Valencia Oranges ripen in late spring and remain on the tree in summer. Fruit do not ripen after harvest.
Storage after harvest: Oranges can last 2-3 months in a refrigerator but must be well ventilated, not in a sealed container.
Leaves: Green, smooth, thick, ovate to lance-shaped. Heavy shade.
Stems: A few spines. Bark is prone to sunscald if not shaded by leaves, especially in higher temperatures.
Roots: Usually grafted onto a special rootstock that is pest resistant and adapted to the local climate. Avoid the Flying Dragon dwarfing rootstock because its limited roots need frequent and careful watering.
Wildlife: Attracts bees, butterflies, birds, mammals, including raccoons which climb the tree to pick the fruit. A caterpillar host plant for the Giant Swallowtail butterfly.
Toxic / Danger: Not to humans. Leaves toxic to pets.
Origin: Southeastern Asia, likely China.

Cultivation and Uses
USDA hardiness zones: 9-11. Frost-tender. Best grown on a south- or east-facing slope above the valley bottom in zone 9a.
Sunset climate zones: 8-9, 12-24.
Chill hours: None.
Heat tolerant: Depends on cultivar.
Sun: Full sun.
Drought tolerant: Depends on rootstock. Drought will damage fruit crop.
Water after becoming established: Every two weeks, to weekly when fruiting in the hottest parts of the summer. Orange tree roots can extend twice as far as the canopy, so water beyond the canopy. Young trees need watering more often than older trees even though older trees consume more water.
Soil: Well drained, can be mixed with aged compost and sand, pH 5.6-8.5 (acidic to alkaline).
Fertilize: Apply a citrus fertilizer mid-February, May, and early October. Follow directions on package. Or, if using organic fertilizer, apply every month from mid-February to early October. Do not fertilize after October to keep the plant from producing new growth that will be harmed by early frost.
Mulch: Keep all mulches at least 1' away from the base of the trunk. Keep grasses and vegetation 3' away from bud union on trunk.
Planting: Place the root ball so that it is slightly higher than the surrounding soil and not at the bottom of a large basin that will cause overly wet soil during rains and subsequent root rot.
Prune: Remove sprouts growing on the trunk under the bud union as they occur. Remove dead, damaged, crossing and weak branches in late winter. When shaping into a tree, unshaded trunks and branches should be whitewashed with a 50% mix of white interior latex paint and water to protect against sunscald.
Litter: Dropped fruit must be picked up immediately to avoid attracting wild animals.
Propagation: Cuttings grafted onto disease resistant rootstock adapted to the local climate. Trees grown from seed are usually true to their parent tree characteristics.
Pests: See Citrus: Diseases and Disorders
Uses: Ornamental, edible fruit.

Comments
The tree pictured is a Seville Orange.



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