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Growing Sweet Oranges: Citrus sinensis

Botanical Overview

Members of the Citrus family (Rutaceae), 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: The flowers attract bees and other pollinating insects. The fruit attracts birds. Mammals may strip the bark off of young trees, consume fallen fruit, or climb the tree to eat the fruit. The leaves are a food source for the Giant Swallowtail butterfly caterpillar – see Pests, below.
Toxic / Danger: Not to humans. The leaves are toxic to pets.
Origin: Asia.

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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.
Drought tolerant: Depends on rootstock. Drought will damage the fruit crop.
Sun: Full sun.
Planting: Place the tree in a sunny location, but with afternoon shade, away from the coldest part of the yard. Do not position the plant next to a frequently watered location, such as grass. Make sure there is enough space for the tree to grow to its full width and height, with clearance to walk around and where overhead lines will not be a problem.
The best time to plant a citrus tree is after the danger of frost is past, in late winter or early spring.
Plant the tree so that the root crown is at least one inch above ground level. The top roots must extend out from the trunk, just above, and uncovered by, soil.
Soil: Well drained, can be mixed with aged compost and sand, pH 5.6-8.5 (acidic to alkaline).
Fertilize: Citrus trees are heavy feeders. 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. Avoid NPK chemical fertilizers because they increase salt build-up in the soil. Do not fertilize after October to keep the plant from producing new growth that will be harmed by early frost.
Water after becoming established: Basin irrigate or deep water, weekly in summer to monthly in winter, from the trunk to just beyond the canopy. The top of the soil should dry out between waterings. The water should reach 1-2' deep for newly planted trees and 3' deep for trees in the ground 3 years or more. Young trees need watering more often than older trees. A sign of insufficient water is leaves turning dull with inward curling edges.
Mulch: Apply organic mulch inside the drip line and 8" away from the trunk to reduce soil evaporation and reduce root zone heat and cold stress. Place a rodent gnaw guard around the trunk at the bottom.
Prune: Citrus trees are best grown as shrubs, so that leafy branches protect their entire trunk from direct sun. Only prune the lowest branches if their tips touch the ground. If you prune up from the bottom to expose the trunk, you must paint it with a tree trunk paint to avoid sunscald. Prune only after danger of the last freeze is over in late winter or early spring. Never prune in the summer.
Remove sprouts growing on the trunk under the graft when they occur because they are from the wrong plant.
Keep the soil under the tree free of grass and other plants that can compete for water and nutrients.
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: April, 2020