Sourced facts

The same wording as on the topic pages, gathered in one list, each with its source.

• Citrus plants won't reliably survive winters outdoors, even in the warmest parts of the UK. RHS
• When grown in containers they can be kept in a greenhouse, conservatory or glazed porch over winter, then moved outdoors in summer into a sunny, sheltered spot. RHS
• Growing citrus as houseplants is not ideal long term, as most prefer a cool spell in winter and a more humid atmosphere than centrally heated homes usually provide. RHS
• The fruit ripens slowly, for up to a year, so plants often carry flowers and fruit at the same time. RHS
• Most citrus form attractive small trees or shrubs less than 1.5m (5ft) tall, so are ideal for growing in containers. RHS
• If you are new to growing citrus fruit, the RHS says it is best to start with one of the easier types, such as lemons. RHS
• Certain varieties of kumquats, limes and calamondin oranges can also be fairly straightforward. RHS
• Look for varieties with an RHS Award of Garden Merit (AGM), which shows they performed well in trials. RHS
• Most commercially sold citrus plants are grafted to ensure they fruit at an early age. RHS
• Ungrafted plants may take up to ten years to fruit. RHS
• Citrus plants are self-fertile, meaning you only need one plant to produce fruit. RHS
• Some lemons, for example, will be fine as low as 5 degrees C (42 degrees F). RHS
• Kumquats often need 7 degrees C (45 degrees F) or more. RHS
• Limes and grapefruits should be kept above 10 degrees C (50 degrees F). RHS
• Calamondin oranges need at least 13 degrees C (55 degrees F). RHS
• In summer, water citrus plants regularly, ideally with rainwater. RHS
• Overwatering in winter is one of the commonest problems, so err on the dry side, and never leave pots standing in water, as this can cause the roots to rot. RHS
• From late March to October, apply summer citrus feed, which is high in nitrogen. Then from November to mid-March, switch to a more balanced winter citrus feed. RHS
• The RHS notes that calamondins make attractive plants and the fruit is great in preserves. RHS
• The RHS describes the kumquat (Citrus japonica, AGM) as having oval orange fruits with sour flesh and a sweet rind. RHS
• The RHS says a plant about 1m (3ft) tall should be allowed to carry no more than 20 fruits at one time. RHS
• Only kumquats, with their much smaller fruits and bushy style of growth, can successfully carry a heavy crop without any need for thinning. RHS
• The RHS lists a huge range of citrus plants to choose from, including lemons, oranges, mandarins, limes, grapefruits, kumquats, limequats, calamondin oranges, tangelos and citrons. RHS
• Citrus is a genus of plants belonging to the rue family (Rutaceae), yielding pulpy fruits covered with fairly thick skins. Britannica
• Economically important plants in this group include the lemon, lime, sweet orange, sour orange, tangerine, grapefruit, citron and shaddock. Britannica
• Yuzu is the most cold-resistant of all citrus fruits, capable of growing at high altitudes at temperatures just above freezing, and is most commonly associated with Japan and Japanese cuisine. Britannica
• Citrus plants are typically evergreen trees or shrubs with glossy oval-shaped leaves; many species have thorns. Britannica
• The flowers are usually white with five petals and are very fragrant. Britannica
• The fruits are a type of modified berry known as a hesperidium, and the flesh is divided into segments packed with tiny juice-filled vesicles. Britannica
• The peel, or rind, of the fruits is leathery and studded with oil glands. Britannica
• The lemon (Citrus x limon) is a small tree or spreading bush of the rue family and its edible fruit. Britannica
• Citric acid may amount to 5 percent or more by weight of the lemon's juice, which is also rich in vitamin C. Britannica
• The lemon was introduced into Spain and North Africa sometime between the years 1000 and 1200 CE. Britannica
• In 1494 the fruit was being cultivated in the Azores and shipped largely to England. Britannica
• The lemon was thought by Linnaeus to be a variety of citron (Citrus medica), though it is now known to be a separate hybrid species. Britannica
• The lemon plant forms an evergreen spreading bush or small tree, 3-6 metres (10-20 feet) high if not pruned. Britannica
• The fruit is oval with a broad, low, apical nipple and forms 8 to 10 segments. Britannica
• The white spongy inner part of the peel, called the mesocarp or albedo, is nearly tasteless and is the chief source of commercial grades of pectin. Britannica
• The relatively cool, equable climatic zones of coastal Italy and California are especially favourable for lemon cultivation. Britannica
• Lemon trees usually bloom throughout the year, and the fruit is picked 6 to 10 times a year. Britannica
• The fruit is usually picked while still green and, after curing, may be kept three months or more in storage. Britannica
• Young lemon trees reach bearing age as early as the third year after planting, and commercial crops may be expected during the fifth year. Britannica
• The average orchard yield per tree is 1,500 lemons a year. Britannica
• A lime, in Britannica's wording, is any of several species and hybrids of trees and shrubs of the genus Citrus (family Rutaceae), widely grown in tropical and subtropical areas for their edible acidic fruits. Britannica
• The Persian lime (Citrus x latifolia) is one of the most common commercial varieties, though the smaller key lime, or Mexican lime (C. x aurantifolia), is also economically important in many places. Britannica
• The tree seldom grows more than 5 metres (16 feet) high and if not pruned becomes shrublike. Britannica
• The fruit is usually about 3 to 4 cm (1 to 1.5 inches) in diameter, oval to nearly globular, often with a small apical nipple, and the peel is thin and greenish yellow when ripe. Britannica
• Most limes exceed lemons in both acid and sugar content. There are, however, some varieties so lacking in citric acid that they are known as sweet limes. Britannica
• Wild limes probably originated in the Indonesian archipelago or the nearby mainland of Asia. Britannica
• Arabian traders may have taken limes, as well as lemons, from India to the eastern Mediterranean countries and Africa about 1000 CE. Britannica
• Christopher Columbus took citrus seeds, probably including limes, to the West Indies on his second voyage in 1493. Britannica
• Limes contain vitamin C (ascorbic acid) and were formerly used in the British navy to prevent scurvy, hence the nickname "limey," in Britannica's wording. Britannica
• The fruit and leaves of the Thai lime, or makrut lime (C. hystrix), add distinctive flavour to the cuisines of Southeast Asia. Britannica
• Finger limes (C. australasica), native to Australia, are noted for their discrete juice vesicles, sometimes called "lime caviar." Britannica
• Britannica treats the kumquat as genus Fortunella, evergreen shrubs or trees of the family Rutaceae, grown for their tart orange fruits. Britannica
• Native to eastern Asia, these small trees are cultivated throughout the subtropics. Britannica
• Kumquat fruits may be eaten fresh, or they may be preserved and made into jams and jellies. In China they are frequently candied. Britannica
• Kumquat plants reach about 2.4 to 3.6 metres (8 to 12 feet) high. Britannica
• The bright orange-yellow fruit is round or oval, about 2.5 cm (1 inch) in diameter, with mildly acid juicy pulp and a sweet, edible, pulpy skin. Britannica
• The oval, or Nagami, kumquat (Fortunella margarita) is the most common species, native to southern China. Britannica
• The egg-shaped Meiwa kumquat (F. crassifolia) has both pulp and rind that are sweet, and is widely grown in China. Britannica