Citrus - Citron, Grapefruit, Lemon, Lime, Orange, Shaddock
DESCRIPTION: These plants are native to the southern and southeastern mainland of Asia and the bordering Malayan islands. They are small, spiny shrubs or trees with alternate, usually evergreen, leaves, which are shiny and leathery and dotted with oil glands. The stems are mostly winged and jointed with the leaves and there is usually a spine on the twigs at the attachment of each stem. Their flowers smell sweet and they have five petals that are white and some kinds have purple staining the outer surfaces. The fruits are spherical or egg-shaped and have 8-14 juicy sections containing large, white or greenish seed leaves (cotyledons). These trees are cultivated in orchards or groves and in gardens where the climate and soil are suitable and as greenhouse plants. Florida and California produce an abundant supply of Citrus fruits. Citrus trees require a minimum winter temperature of 45-50 degrees. Citrus fruits are prized for their health values. Oils, pectin, flavorings, perfumes and other by-products are secured from their flowers and fruits. Citrus is used as a group name for the fruits of theses plants as well as for certain fruits now classified in groups other than Citrus. Only eight are important horticultural plants:
Citron (Citrus medica) - This was the first Citrus fruit that was introduced to Europe by the armies of Alexander the Great about 300 BC. It found a suitable home in the Mediterranean region where it has been cultivated from that time to the present. It grows as an irregular, open-headed shrub or small tree with large, light green leaves. The flowers are painted purple on the outside and are followed by large, oblong or ellipsoid fruits. The peel is very thick and is rough and yellow on the outside and white inside. The pulp is small and greenish and the juice is scarce and very acid in most types. They were originally grown in Europe out of interest for its fragrant fruits, but later, the white pulp was used raw, being served as a salad or with fish. A method of candying the peel was developed and candied peel is now the main Citron product. Southern Italy, the island of Corsica and some Greek islands grow nearly all the Citrons. This fruit is very tender, maybe the least resistant to winter temperatures of all the Citrus fruits because of its continuous growth tendency.
Grapefruit (C. paradisii) - This is a vigorous tree that reaches a height of 30 to 50 feet. It has a round, thick head of foliage. Its leaves are large, egg-shaped (ovate) and blunt pointed. Their large flowers are white and are produced singly or in axillary clusters. The fruits are larger than the Orange and are usually in bunches. They are light yellow and have silvery white or pink flesh. The white seeds are larger than the Orange's. The flavor is a blend of acid, sweet and bitter. The exact origin of the Grapefruit is unknown. It was mentioned as growing in Barbados as early as 1750. The name Grapefruit was used for it in Jamaica before 1814. It was brought to Florida by Dr. Odette Phillipi, a naval surgeon under Napoleon, who settled near Safety Harbor in 1823 and developed a grove. From then on to now the Grapefruit has become commercially cultivated in Florida, where it is grown abundantly.
Lemon (C. Limonia) - This is a small, widely branched tree that grows 10 to 20 feet high. It is thorny and evergreen and its leaves are narrow and ovate and light green. The flower buds are in pairs or single. They are tinted purple. The petals are white inside and purple on the outer surface. The fruit is usually pointed at both ends and light yellow. Its flesh is light and its juice sacks are thin. The seeds are ovoid and smooth. The Lemon is grown for its acid juice, which is used in flavoring and in making various drinks. Lemon peel is candied. Lemon trees are grown as pot plants and outside in regions fairly free of frost. It is commercially important in California; Spain and Italy mostly stock the European countries. The origin of the Lemon is unclear. Its native home may have been southern China and adjacent parts of Upper Burma, from which it spread into India and westward. It is recorded that by 1150 AD it was growing in Spain, where it was introduced by the Arabs. The Crusaders also had a part in its introduction into western Europe (1096-1271 AD); since then it has been grown there continuously. Columbus brought Lemon seeds and probably fruit with him on his second voyage (he reached Hispaniola on November 22, 1493). It was brought to Florida by the Spaniards, perhaps as early as 1565 and to California about 1769 when the Franciscan fathers started the establishment of the missions.
Lime (C. aurantifolia) - This evergreen tree is small, spiny and irregularly branched. Its small, elliptic to oblong leaves are pale green. The white flowers are small and produced in axillary clusters. The fruit is small, roundish and thin-skinned. The pulp is greenish and in sections of about ten. The juice is acid with a distinctive flavor. The Lime is a native of the East Indies and has spread all over the world in tropical and near tropical regions. It was brought to America by the Spaniards and became widely scattered throughout the West Indies. It was taken to Florida and in the southern parts has become naturalized. From Mexico, it was carried into California. While most Limes are acid, there also are sweet kinds grown and used in some of the areas where the acid ones are grown. Limes are gathered when fully grown, but still green, and shipped very soon after. The fruit is used in much the same way as Lemon.
Mandarin Orange (C. nobilis deliciosa) - This small, spiny tree has thin branches and twigs. Its leaves are small and elliptic to lanceolate. The flowers are small and white and produced singly or in small clusters. The oblate (often very flattened at the ends) fruits are orange to orange-red with a loose rind that comes off easily. The 9-15 fruit sections are loosely attached to the rind and one another. The pulp is deep orange, sweet or fairly acid. The green seeds are numerous. This tree is native to southeastern Asia. The fruit yields a high quality juice and is used as a desert fruit.
Shaddock (C. maxima) - This large tree has a round top with fuzzy twigs when young. Its huge leaves are ovate. The white flowers are borne singly or in bunches. The fruit is the largest of all Citrus. It is globose, oblate or moderately pear-shaped with 11-14 sections. The pulp is light colored or pink and coarse with large, spindle-shaped juice sacks that separate easily from one another. This tree is a native of southeastern China, where it's grown for its fruit. In the Citrus districts of the U.S. it is cultivated as an ornamental tree and is interesting because of its very large fruits. It is closely related to the Grapefruit, but much less cold resistant. The Shaddock was brought to the Barbados by Captain Shaddock, of an East Indian ship. It bears his name in English speaking countries. Pummelo is another name for it.
Sour Orange (C. Aurantium) - This small, spiny tree grows up to 30 feet high and has a compact, rounded top. Its leaves are ovate and fragrant when crushed. The fruit is orange or reddish-orange with a rind that is rough, strong scented and bitter. There are 10-12 fruit sections and the pulp is acid. The Sour Orange is grown extensively in some Citrus regions for its fruit, which is used in making marmalade. In areas where it grows, it's used for making acid fruit drinks that are very agreeable in warm weather. It is much hardier than the Sweet Orange. The Sour Orange was the first Orange grown in Europe, where it was introduced in the eleventh century by the Arabs. For several centuries it was the only Orange grown there. It is naturalized in Florida and is often met with in old Orange groves where the Sweet Oranges budded on it have died. In humid climates it is prone to a fungus disease commonly known as "Scab".
Sweet Orange (C. sinensis) - This is a medium-sized tree (25-40 ft.) with a compact round-oblong head. The leaves are ovate to ovate-oblong. The fragrant, white flowers grow in small clusters on the new growth. The well-known fruit is round or ovoid and colored orange to reddish-orange. The juicy flesh is orange and fairly acid and there may be few or many seeds. This Orange is native to southern Asia. It was introduced to Europe in the latter part of the 15th century and was brought to America (Hispaniola) by Columbus on his second voyage in 1493. It was growing abundantly in St. Augustine, Florida by 1579 and must have been brought there when the settlement was founded in 1565 or very shortly thereafter. The Sweet Orange probably came to the Franciscan mission at San Diego, California when it was founded in 1769 from Mexico. Sweet Oranges are grown extensively in all parts of the world suitable for their culture. Production in the U.S. has reached many million boxes, the largest producing areas being Florida and California. They are also grown in Texas and other Gulf Coast States and in Arizona.
Hybrids - Most of the Citrus hybridize quite easily and a large number of hybrids have been created. Many of these aren't superior to the originals, but others are worth while. The Tangelo is a hybrid between the Grapefruit and Tangerine. It is one of the best of the hybrid Citrus fruits and some varieties are grown commercially in Florida. Another one is the Citrange. It is a hybrid between the Sweet Orange and the Trifoliate Orange (Poncirus Trifoliata). These are the hardiest of the edible Citrus fruits and succeed 300-400 miles north of the regular Florida citrus belt. None of the varieties have fruits suitable for eating out of hand, however, their main value is for making ades and preserves. They're also used as understocks upon which to graft the Satsuma Orange. Citrange fruits are 2-3 inches in diameter. The Citrangequats are the results of hybridizing Citranges with Kumquats. Like Citranges they are hardier than other kinds of Citrus and the are used for making ades and preserves. Limequats are hybrids between the Marumi Kumquat and the West Indian Lime. They are about as hardy as Kumquats. Their fruits are about 2 inches long. The variety Eustis is best known.
The Kumquat (Fortunella) and Trifoliate Orange (Poncirus), mentioned above and both less important, are also included under the common name Citrus, but don't belong in the botanical group Citrus.
POTTING: Outdoor cultivation - Citrus fruits can be produced on several kinds of soil from light sandy kinds to clayey, stiff kinds. The ideal, but rarely found, is loamy soil that holds moisture, has adequate drainage and full of vegetable matter. Even though soil can be enhanced by adding fertilizer and organic matter, it's better if the soil is naturally high-grade. In many places, a great supply of irrigation water must be available and freedom from harmful winter temperatures is necessary. Valleys should be avoided because there is risk of injury from cold and good air circulation is needed. The land chosen for growing Citrus should be prepared a year in advance. They flourish in soil that contains a great amount of vegetable matter. This can be accomplished by growing crops of Crotalaria, Indigofera, Vicia and other legumes and turning the soil under. This also increases the nitrogen content of the soil. The soil should be thoroughly broken up before the trees are planted. These trees grow to different sizes, therefore, they must be planted different distances apart. These distances are usually used: Grapefruit, 30 feet; Sweet Orange, 25-30 feet; Tangerine, 20-25 feet; Lemon and Lime, 20 feet; and Kumquat, 15 feet. To figure out how many trees may be planted per acre divide 43,560 (the number of square feet in an acre) by the square feet of the distance used for setting the trees. Usually Citrus trees are planted during their dormant season in winter. Before planting, the trees should be pruned to reduce the foliage and the number of branches. No more pruning will be needed until after the first growing season, when 3-4 branches should be selected to form the framework of the tree and others are removed. The holes should be larger than the spread of the roots. Fill the bottom of the holes with good soil to bring the trees to the right level. They shouldn't be planted any deeper than they grew. The roots should be carefully spread out and soil should be filled around and between them and carefully packed. Water when the holes are partially filled and a small amount of Citrus fertilizer mixed with the soil is helpful. A pint per tree is about right. The ground right around the trees needs to be kept free of weeds. The rest of the ground should be planted with a cover crop of legumes. In early spring, the beginning of summer and in early fall, fertilizer containing nitrogen, phosphorus and potash, with traces of copper, zinc, iron and other minerals should be applied close to, but not against the trees. In the autumn fertilizing, nitrogen in the fertilizer should be eliminated or greatly reduced. In the fall, the cover crop should be turned under and the ground left bare for the winter. This helps lessen the damage from the cold. Heaters are used to raise the temperature during cold spells. The ground is usually cultivated for a time during the spring and then a cover crop is started for the summer months. Many diseases and pests attack Citrus trees and are mainly controlled by spraying and dusting with insecticides and fungicides. Methods followed and materials used change from time to time, so definite information can be acquired from Agricultural Agents and other sources.
Greenhouse cultivation - When used as greenhouse plants, they are planted in large pots or tubs filled with fibrous loam, enriched with a little dried cow manure and a few lumps of crushed charcoal. A bit of bone meat added to the soil is beneficial. They need a minimum winter temperature of 45-50 degrees. Repotting young plants should be done in early February or March, but once they are established in large tubs or pots, they may remain there for several years. Established plants benefit from weekly doses of liquid fertilizer from May to September. During the summer months the soil should never become dry. The leaves should be sprayed frequently with clear water. Adequate ventilation is necessary in warm weather and shade is needed from strong sunlight. During the winter, water is only given when the soil becomes dry and the leaves should only be sprayed at midday on warm days. The tips of straggling shoots should be removed in March. The fruits need about 12 months to reach maturity.
PROPAGATION: Outdoors - Seedlings of different kinds, mainly Rough Lemon, Sour Orange, Sweet Orange and Trifoliate Orange are grown to furnish stocks on which different Citrus varieties are budded. Seeds are carefully squeezed out of the fruits and washed free of pulp and juice and surface dried then planted at once or stored for a short time by mixing them with pulverized charcoal in tight containers. They should not be allowed to dry out or else they will be worthless. Rows should be 16 inches apart and the seeds planted thickly three-fourths of an inch deep. Trifoliate Orange can be planted in the fall as soon as the fruit is ripe, the others in spring after danger from frost has passed. During the summer, they should be fertilized and watered and kept free of weeds. Usually the seedlings remain in the seedbed for two seasons but they can be transplanted sooner to rows 4 feet apart and 16 inches apart in the rows. Here again they are cultivated and fertilized. When the diameter of the stems reaches one-half to three-fourths of an inch, they are ready for budding. The best times to do this are in late summer just before growth ceases or in the spring after growth starts. Shield budding with an inverted T incision is the method most commonly used. Buds inserted in late summer remain dormant until the following spring when the tops of the stocks are cut off just above the point of insertion. This forces the buds into growth. Sprouts from the stocks are broken off and the shoots from the inserted buds are trained to stakes to keep them straight and safe from injury. When they are 30 inches, the young trees are usually cut off to force branching. They are usually left to grow for two seasons before transplanting. Cuttings from Citron, Lemon, or Otaheite Orange form roots easily; others such as Sweet Orange, Mandarin Orange and Grapefruit are more difficult to start. Terminal parts of branches or twigs, 4-6 inches long, cut evenly across their bases, are best. Remove all but 3 or 4 upper leaves. Dip the cuttings in a root-inducing hormone and insert half their length in clean sand. A closed frame with bottom heat, is a great help in rooting. When they have formed roots, they are potted and handled as are cuttings of other kinds.
Greenhouse - When growing Citrus trees in the greenhouse, seeds can be sown, 1 inch deep, in pots of sandy, loamy, soil and placed in a propagating case in the spring or summer. The seedlings can be potted in 3-inch pots. They are slow in producing flowers, though, and are generally used as stocks for grafting. This is done in March, using the splice method. Cuttings will also produce plants. Shoots, 3-5 inches long, can be inserted, along with a "heel" or piece of the old branch attached, into sand and peat moss in a propagating case in August. New plants can also be obtained by layering the branches and by air layering, in early summer.
Citron, (C. medica) - Main varieties: Corsican and Etrog.
Grapefruit, (C. paradisi) - Varieties: Duncan. Fruit med. to lg.; more resistant to lower temperatures than others; valued as fresh fruit & for processing. Marsh. Fruit med.; valued as fresh fruit, not suitable for canning. McCarty. A favorite variety in the Indian River section of Florida. Ruby. Fruit med. to lg.; grown for fresh fruit. Triumph. Valuable for the home garden.
Lemon, (C. Limonia) - Varieties: Eureka. Fruit med.; Very acid; A favorite commercial variety. Lisbon. Fruit med.; very acid; grown for commerce in California; thought to have originated in Portugal. Meyer's. Fruit sm. More cold resistant than other Lemons & very fruitful. Introduced from China by the late Frank N. Meyer. Otaheite. Fruit sm. to med.; insipid sweet. Sometimes classed with Limes, but purple flower buds and outer petal surfaces indicate that it's a Lemon. It's a small shrub usually raised from cuttings and grown in pots; very pretty when in flower and fruit. Ponderosa. Also known as American Wonder. Fruit very lg.; grown as an ornamental and garden fruit. Rough. Fruit med.; acid juice. Seedlings are used as understocks. Villafranca. Fruit med. to lg.; a favorite variety in Florida, imported form the Mediterranean region by General Stanford about 1875.
Lime, (C.aurantifolia) - Varieties: Bearss. Fruit med.; very acid juice; seedless. Favorite commercial variety of California, where it was said to have originated as a seedling. Mexican. This represents a group of similar seedlings. Fruit sm. A few distinct varieties such as Everglade, Palmetto and Yung have been selected, named and propagated from the Mexican Lime complex, but for the most part, seedlings are planted. Rangpur. Very acid juice, grown as a garden plant. Tahiti, also known as Persian. Fruit lg.; distinct lime flavor. Favorite variety in southern Florida where it's grown for fresh fruit and for juice that is processed.
Mandarin Orange, (C. nobilis deliciosa) - Varieties: Cleopatra. Valued as an ornamental. Used to some extent as an understock. Dancy. Fruit med. and juicy. The most important variety of the group, commonly known as Tangerine, originated in Florida where it's quite extensively grown. King. Fruit lg. and juicy. Satsuma. Fruit of excellent quality. Temple. Fruit lg. and juicy. Calamondin. Fruit sm.; very acid. Used for acid drinks and for high-grade marmalade. Very ornamental and hardy.
Sour Orange, (C. aurantium) - Varieties: Bitter Sweet. Fruit mildly acid. A number of other varieties of Sour Orange such as Bouquet, Myrtle Leaved, Variegated, etc., are grown once in a while.
Sweet Orange, (C. sinensis) - Varieties: Hamlin. Fruit med.; almost seedless, excellent quality. Parson Brown. Very early. Pineapple. Rich flavor, excellent quality. Ruby. Rich flavor, excellent quality. Valencia. The standard late orange. Washington or Washington Navel. Fruit lg.; Seedless; a favorite in California; doesn't do well in Florida.
Shaddock, (C. maxima).
C. Sinenais Navel (Orange)
C. Sinenais Valencia (Orange)
C. Reticulata Cleopatra (Mandarine Orange)
C. Reticulata Ponkan (Tangerine)
C. Rutaceae (Grapefruit)
C. Paradisi Foster (Grapefruit)
C. Madurensis (Calamondin)
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