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Growing Sweet Oranges: Citrus sinensis

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Botanical Overview

Modern citrus fruits, according to genetic analysis, are complex hybrids arising from mandarin, pomelo, and citron ancestors, refined by more than four thousand years of cultivation. Citrus sinensis, the sweet orange, has hundreds of cultivars.


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: All sweet orange cultivars self-pollinate.
Years before fruiting: 5-6 years after grafting, less on some rootstocks. Blood Orange cultivars often start fruiting 2 years later.
Fruit: Round to oval, ripening to yellow or orange. The flesh is juicy and sweet, yellow, orange or red in color, and divided into 10-14 segments. The skin is tight and difficult to peel except on Naval oranges which have thick skin. Seedless cultivars are available. The sweetness of an orange depends on the total amount of sunlight received while on the tree, nothing else.
Months for fruit to ripen: 9-12. The color of an orange is not a reliable indicator of ripeness. Remove one from the tree and taste it to determine if the fruit are ready for harvest. Most Naval Oranges ripen in winter or early spring and should be harvested by the time new flowers begin to bloom. Valencia Oranges ripen in late spring and can remain on the tree until September. Oranges do not ripen further 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, providing heavy shade.
Stems: A few spines may be present. The bark is prone to sunscald if not shaded by leaves, especially in higher temperatures.
Roots: Orange trees are usually grafted onto a special rootstock that is adapted to the local climate.
Cultivars of Note:
'Blood Orange' An orange with dark red flesh, and a flavor that includes raspberry notes among the citrus. The color is most pronounced in cooler weather.
'Cara Cara' A red-fleshed naval orange, with an excellent, complex flavor. Extra sweet, low in acidity.
'Naval' An orange grown for fresh eating.
'Valencia' An orange with high vitamin C levels primarily used for juice.
Wildlife: Attracts bees, insects, birds, and is a food plant for the Giant Swallowtail butterfly caterpillar – see Pests, below. Mammals may strip the bark off of young trees, consume fallen fruit, or climb the tree to eat the fruit.
Toxic / Danger: Not to humans. The leaves are toxic to pets.
Origin: Asia.

Cultivation and Uses

USDA hardiness zones: 9-11. Frost-tender. Best grown on a south- or east-facing slope above valley bottoms in zone 9a.
Chill hours: None.
Heat tolerant: Depends on cultivar.
Sun: Full sun.
Drought tolerant: Depends on rootstock. Drought will damage the fruit crop.
Water after becoming established: Deeply, monthly in winter to weekly in summer, from the trunk to just beyond the canopy. Young trees need watering more often than older trees even though older trees consume more water. A sign of insufficient water is the leaves turning dull and curling inward from the edges.
Soil: Well drained, can be mixed with aged compost and sand, pH 5.6-8.5 (acidic to alkaline).
Fertilize: Do not fertilize the first two years. Apply an organic fertilizer, every month, from mid-February to early October. Apply a citrus micronutrient solution three times a year in February, May and August. 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 the bud union on the trunk.
Planting: Place the root ball so that it is slightly higher than the surrounding soil.
Prune: Remove sprouts growing on the trunk under the bud union as they occur because they are from the wrong plant. Remove dead, damaged, crossing and weak branches in late winter. When shaping into a tree, unshaded trunks and branches should be painted with a tree trunk paint 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: The Giant Swallowtail Butterfly caterpillar. This larvae resembles bird poop and has white and black and/or brown splotches. On a large plant it will cause no harm. On a small plant, relocate it to a large citrus. See Citrus: Diseases and Disorders
Uses: Edible fruit, ornamental.

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Sweet Orange: Citrus sinensis - flowers

Sweet Orange: Citrus sinensis - fruit

Sweet Orange: Citrus sinensis

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Latest update: February, 2020