Sweet orange

Family

Rutaceae

Habit

Tree

Height

8.5 m

Spread

8 m

Growth

medium

Lifespan

200 years

First yield

after 7 years

Full yield

after 200 years

Yield per plant

up to 200 kg a year

Yield in cultivation

up to 40 t/ha

Energy yield

1800 kcal per m² a year

Hardiness

zone 10–12

Shade tolerance

full sun

Soil

Sand, Silt, Loam

Soil moisture

semi-dry – very moist

pH

5.5 – 7

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

Edible: The orange is the most widely grown citrus fruit in the world and is processed mainly as juice. The juicy segmented flesh is eaten raw, pressed, in salads, desserts and sauces; the grated peel flavours baking and sweet dishes, and the flowers are made into tea and syrup. Four groups of varieties are distinguished: the ordinary blond oranges, the seedless navel oranges with their characteristic navel at the blossom end, the red-fleshed blood oranges whose colour develops only where day-night temperature differences are large, and the rare acid-free oranges. For good flavour the fruit needs an annual mean above eighteen degrees. In Europe it is harvested from August to May; the fruit does not ripen after picking, and oranges taken unripe stay sour.

Medicinal: Historically the orange matters above all as a source of vitamin C: citrus fruit was the means by which scurvy was fought at sea from the 18th century onwards, and this connection is one of the few things about the plant that is scientifically secure. Alongside it stands a broad tradition. Dried peel counted as a bitter for stimulating digestion and went into stomach bitters and liqueur recipes. Orange flower water and the neroli oil obtained from it were used in folk medicine as a calming remedy for restlessness and difficulty sleeping, a use still found in aromatic preparations today. For none of these applications is there evidence of efficacy in the modern sense.

Other uses: Beyond the fruit, practically everything on an orange is used. Cold pressing the peel yields orange oil, which goes into perfumery, cosmetics and the flavour industry and, thanks to its limonene content, makes an effective and biodegradable cleaner and degreaser; the flowers give neroli oil, and flowers and leaves together petitgrain oil. The peel also supplies pectin for gelling agents and, dried, a spice. The seeds are pressed for an oil worked into soap. The press residues of the juice industry go into cattle feed as dried pulp. The wood is hard, heavy and durable but splits easily; it is turned, carved and made into handles, and the chips serve as an aromatic wood for smoking food.

Site: In Central Europe the orange is strictly a container plant, and the decisive question is not the summer position but the winter one: it needs bright quarters at about five to ten degrees, cool and light rather than warm and dark. In summer it stands in full sun, warm and sheltered against a south wall or on the terrace, where its scent also suits a seating area. Weight needs thinking about: a mature tub has to be moved twice a year, so a wheeled base belongs in the plan. Frost damages it at around minus two to minus five degrees, so bring it in early. Flowers and ripe fruit often hang on the tree at the same time, because ripening drags on for months. Fallen fruit stains pale paving. Care: The commonest mistake is the water. Oranges need an acid root zone, and hard tap water raises the pH until the young leaves turn yellow with green veins — this chlorosis is corrected with low-lime water and an iron-rich citrus feed. Feed weakly every week from March to August and not at all in winter quarters; water thoroughly and only again once the surface of the compost has dried, since waterlogging causes root rot and sudden leaf drop. Repot in spring into a structurally stable, free-draining medium. Prune sparingly before growth starts, removing inward-growing shoots. In winter quarters scale, mealybugs and red spider mite are the rule if it stands too warm and too dry — keep it cool and check regularly. Harvest once the fruit parts easily; it does not ripen further after picking.

Oranges are almost always grafted. Seed-raised plants germinate readily and, thanks to nucellar embryony, usually give clones identical to the mother, but they take eight to fifteen years to first flowering, stay heavily thorned when young and root shallowly. In commercial growing and in the nursery, budding onto a rootstock in summer is therefore the rule. The rootstock decides hardiness, lime tolerance and disease susceptibility: trifoliate orange, Poncirus trifoliata, gives the greatest winter hardiness but responds to calcareous soil with chlorosis; citrange, a cross of Poncirus and orange, partly compensates for this; sour orange tolerates lime well but is susceptible to tristeza virus. Cuttings of half-ripe shoots root with bottom heat, but produce weaker trees more prone to soil-borne fungi.

The orange is a first-class bee plant — though one that hardly comes into its own in Central Europe. The US Department of Agriculture pollination report rates it at the highest level for both nectar and pollen for honeybees, and as attractive to bumblebees and to solitary bees of the genera Andrena and Xylocopa; beekeepers move colonies into the groves specifically to take orange blossom honey. It does not depend on pollination itself: oranges set fruit parthenocarpically, which is why varieties stay seedless without cross-pollination. Its wildlife value therefore stands or falls with the quantity of bloom, and on a container plant that stays small. It does at least tend to flower while standing outdoors, and the strongly scented blossom is found reliably by honeybees and bumblebees. It is not a larval food plant for native butterflies or moths.

Special features: needs an annual average above 18°C for good flavour; in the tropics the peel stays green despite ripeness; cross of mandarin x citron; so significant that we named the colour after the fruit, not the other way round; There are 4 groups: blond oranges (common), navel oranges (with navel), blood oranges (red-fleshed), acidless oranges (uncommon);

East Asia: the orange is not a wild species but a cross between mandarin and pomelo that arose in China or South-East Asia. There are therefore no wild populations — every orange goes back to vegetatively propagated cultivated forms. In Europe it cannot be traced before the 15th century; the bitter orange already known in medieval Italy is a different species. From about 1500 Portuguese seafarers spread markedly better varieties after the sea route to India was opened, following Vasco da Gama's report of superior oranges at Mombasa in 1498. Today it is grown throughout the subtropics; the largest producers are Brazil with around 15.7 million tonnes, China with 7.6, Mexico with 4.8, Egypt with 4.2, India with 3.9 and Spain with 2.9 million tonnes a year.

The orange has no natural habitat: it arose as a hybrid in cultivation and occurs nowhere in the wild. What defines its site is therefore the requirement of the crop. It needs a frost-free subtropical climate with an annual mean above eighteen degrees, mild winters and long warm summers; frost damages leaves and fruit at only a few degrees below zero. It calls for deep, free-draining, slightly acid soils without waterlogging and a steady water supply, secured by irrigation in the classic growing regions of the Mediterranean and California. Climate also shapes the fruit: in the tropics the peel stays green despite full ripeness because the nights are too warm, and blood oranges develop only where the day-night difference is large.