HOME FRUIT PRODUCTION-MANDARINS
Julian W. Sauls
Professor & Extension Horticulturist
Mandarins include a diverse group of citrus fruits that are characterized by bright peel and pulp color, excellent flavor, easy-to-peel rind and segments that separate easily. Because all tangerines are mandarins but not all mandarins are tangerines, mandarins are commonly separated into four groups: Mediterranean, king, satsuma and common tangerines. Of these, satsumas and tangerines are of most interest in Texas.
Most mandarin trees are more erect than other kinds of citrus trees and many exhibit a drooping habit because of rather long, willowy branches. The wood is somewhat more brittle than other citrus and limb breakage is common under heavy fruit loads unless some sort of support is provided. Most varieties of mandarins are self-pollinated and self-fruitful, but some of the hybrids are self-incompatible and will produce few fruit without the presence of suitable pollenizer varieties nearby. Mandarins tend to alternate bearing, with a heavy crop in one year followed by a lighter crop in the next season.
Mandarins are grown in tropical and subtropical areas worldwide, although best color and quality usually occurs under subtropical conditions. As a group, mandarins are among the most cold hardy of citrus fruits, being second only to kumquats. Small orchards of tangerines in the Carrizo Springs area and of satsumas in southeast Texas were fairly common until the severe freezes of the 1980's. Few of those orchards remain today, but interest in mandarins remains high for home production. Protection during severe freezes will be essential to successful mandarin production.
SOILS AND SITE SELECTION
Mandarins are well-adapted to all well-drained soils in virtually all of Texas along and south of U.S. Highway 90 from Del Rio to Orange--depending on rootstock. In southeast Texas, growers prefer trifoliate orange rootstock because of the additional cold hardiness which it imparts to the tree. However, trifoliate orange is poorly adapted to the saline conditions and alkaline soils which predominate in south Texas where sour orange is the rootstock of choice. Trees on trifoliate are considerably smaller than trees on sour orange, with those on 'Flying Dragon' trifoliate being even smaller than on other trifoliate rootstocks. Smaller trees are more easily protected during severe freezes, but smaller trees are also less productive.
In the home landscape, mandarins should be planted on the south or southeast side of the house for maximum protection from cold weather. Overhanging trees will provide additional cold protection but the competition for light, water and nutrients will reduce mandarin tree growth, production and fruit quality.
VARIETIES AND TYPES
The Mediterranean group of mandarins apparently originated in the Mediterranean basin, most likely in Italy. 'Willowleaf' or 'Mediterranean' is the most prominent variety. Its fruit are of medium size, oblate, with a short collar and furrowed neck on the stem end. The rind is thin and both rind and flesh color are yellowish-orange at maturity in October-November. The fruit usually have 20-25 seeds. Most mandarins of this group have small, willow-shaped leaves and a droopy growth habit.
The King group of mandarins apparently originated in Vietnam. 'King', the primary variety, was introduced to California about 1880. 'King' fruit is among the largest of all mandarins; its rind is thick, rough and yellowish-orange at maturity. The flesh is deep orange in color; the fruit are very seedy and somewhat late in maturity (February-March). Unlike most mandarins, the cotyledons of 'King' seed are cream colored rather than green.
Satsumas are probably the most important citrus in Japan where they are referred to as Unshu mandarins. A number of varieties originated there, the most well-known being 'Owari', the quality of which surpasses all other satsumas in Texas. 'Obawase', 'Okitsu', 'Kimbrough', 'Big Early' and 'Armstrong Early' are other varieties grown in southeast Texas. Characteristics of the most common varieties grown in Texas are shown in Table 1. A number of other varieties and selections exist, but most of the latter are no different from 'Owari'. Satsuma fruit are of superb quality and nearly completely seedless. Peel color is bright reddish orange and the peel is easily detached from the fruit at maturity. The segments are readily separated, also. The fruit attains best quality under cool temperature conditions during fall and winter; thus, quality is usually better in the more northern limits of its range. Satsuma fruit, like that of most mandarins, tends to dry out and become "ricey" if not harvested soon after it matures.
Tangerines are the most important of the mandarin groups, both because of their widespread culture and because of their use in citrus hybridization. 'Clementine' ('Algerian') originated in Algeria and was introduced to the U.S. in 1909. It has deep reddish orange color and both the rind and segments exhibit slightly more adherence than most mandarins. Fruit of 'Clementine' matures earlier than 'Dancy' and it is usually smaller; the fruit will store on-tree better than most.
'Dancy' a major variety that achieves deeper color and larger size than 'Clementine', but the fruit do not hold well on-tree after maturity. Its later maturity puts 'Dancy' fruit at greater risk of losses to cold. 'Dancy' originated in 1867 as a seedling of a tangerine brought from Tangiers to Florida. It is best adapted to Florida's high humidity and heat, although it is grown in other areas.
'Ponkan' ('Warnurco', 'Chinese Honey') apparently originated in India where seedlings orchards are still widely grown. It is believed to have been sent to Florida from China in the early 1890's. Its fruit are generally large for mandarins, having orange rind and flesh. The flesh is tender and melting, with mild flavor and aroma.
'Changsha' is a seedling tangerine that was once popular in Texas landscapes because of its relative cold hardiness. The author saw two mature trees in production at the O.S. Gray nursery in Arlington, TX, in 1973. Trees grown from seed are more cold tolerant than budded trees.
'Fortune' arose from the hybridization of 'Clementine' and 'Dancy' tangerines. It achieved some importance in South Texas because of its late maturity, but such lateness would be considered undesirable in colder areas of its range in Texas.
There are dozens of other varieties of tangerines, but few have achieved the prominence of those described above and in Table 1.
Tangerines have been widely hybridized with other citrus, primarily grapefruit. Some of the resultant hybrids have, in turn, been hybridized with tangerines, oranges and each other, resulting in some confusion in nomenclature. In the simplest hybridizations, a cross between tangerine and orange is called a tangor, while a cross between tangerine and grapefruit is called a tangelo. When a tangelo is further hybridized with tangerine, or when two tangelos are crossed, the result is considered a tantangelo. Hybrids that include tangerine, grapefruit and orange are simply called citrus hybrids.
Of the hybrids, only tangelos are classified by their parentage, i.e., tangelo; the rest are classified as the type of citrus which the respective hybrid most closely resembles and by which the industry commonly refers to it. For example, 'Ambersweet' hybrid is a cross between an unnamed sweet orange seedling and a tantangelo (tangerine X tangelo). Because its makeup is one-half orange, three-eights tangerine and one-eighth grapefruit, and because it looks more like an orange, 'Ambersweet' is called an "orange". By contrast, 'Page' "orange" is a tantangelo hybrid that resembles an orange, despite the fact that it has no orange heritage.
The classification and heritage of the most common mandarin hybrids are presented in Table 2, which should help clarify questions of nomenclature as well as concerns that the author failed to include a number of important "tangerine" varieties in the previous section on tangerines.
Fruit characteristics of these mandarin hybrids are presented in Table 3.
The origins of the two most notable tangors, 'Temple' and 'Murcott', are somewhat obscure. 'Temple' apparently originated in Jamaica and was introduced to Florida about 1896--although it was not named until 1919. The tree is rather thorny and is undoubtedly the most cold-sensitive of all mandarins and mandarin hybrids. Indeed, its lack of cold hardiness is a major reason that 'Temple' has not succeeded in the Texas citrus industry. 'Murcott' is believed to be a tangor of unknown origin that resulted from the breeding program of the U.S.D.A. prior to about 1916. Its peel is very thin and tightly adherent. The flavor of 'Murcott' is excellent, ranking with 'Owari' satsuma and 'Ponkan' as the author's top three citrus fruits in flavor and quality for eating out-of-hand.
'Orlando' and 'Minneola' are the two most prominent tangelos, although 'Thornton was once common in south Texas. 'Orlando' is very similar to a seedy orange, although the number of seed as well as fruit size and productivity depend upon cross-pollination from pollenizer varieties. A notable characteristic of 'Orlando' is that its leaves are distinctly cupped rather than flat.
'Minneola' is also known as 'Honeybelle' in Florida. Its fruit have a large neck at the stem end; fruit are very juicy and flavorful. It also requires cross-pollination.
Few of the tantangelos have achieved prominence in Texas landscapes, although occasional trees of 'Fairchild' and 'Bower' can be found in the Valley. 'Bower' was jointly released by the Texas Agricultural Experiment Station and the U.S.D.A. in 1973. 'Sunburst' is a relatively recent U.S.D.A. hybrid that was introduced to the Texas industry after it passed Texas quarantine requirements in 1981.
Both 'Fallglo' and 'Ambersweet' are of relatively recent origin but neither is available in Texas inasmuch as they have either not been requested by the industry or they have not passed Texas quarantine requirements.
Other mandarin-like fruits that do not fit in the above groupings include 'Cleopatra' mandarin, Rangpur lime, Otaheite Rangpur and calamondin. 'Cleopatra' mandarin is noteworthy only for its use as a rootstock for other citrus. 'Rangpur' lime is not a lime at all but a mandarin-like fruit native to India. It is noteworthy as a potential rootstock for other citrus.
'Otaheite' ('Otaheite Rangpur') is an acidless, semi-dwarf form of 'Rangpur' that is widely grown as an ornamental, often as a potted plant. Calamondin is a small-fruited, acid fruit that is grown as a potted plant that is often called "miniature orange".
PROPAGATION (AND QUARANTINES)
It is important to know that any and all citrus trees planted in Texas must have been propagated in Texas from Texas-grown plant materials, i.e., it is illegal under Texas statutes to import citrus trees, seedlings, plants, budwood or graftwood from any other state or country. Aside from the legal penalties involved, you should understand that violations of the Texas citrus quarantine laws could jeopardize not only home citrus trees from east Texas to south Texas but also the entire Texas citrus industry. At present, the Texas Citrus Budwood Foundation is working diligently to develop virus-free sources of all types and varieties of citrus currently being grown in Texas.
In the meantime, there are reputable Texas nurseries which produce citrus trees for sale to consumers--so you don't have to go to Louisiana or elsewhere to get a quality mandarin tree.
Either T-budding or inverted T-budded onto appropriate seedling rootstocks is the preferred means of propagation in Texas. As previously noted, trifoliate orange stocks are preferred in southeast Texas while sour orange stocks are better adapted to all of Texas where mandarins can be grown--including southeast Texas. 'Changsha' and the mandarin-like fruits discussed in the previous two paragraphs can be grown from seed, while those used primarily as potted plants are usually propagated from semi-hardwood cuttings under mist.
PLANTING AND ESTABLISHMENT
For the most part, mandarin trees will be purchased from a nursery rather than grown at home. Generally, the trees will be container-grown in a soilless medium--which makes the trees rather difficult to establish without special care. At planting, use a gentle stream of water from the garden hose to wash an inch or so of the medium from all around the root ball, thereby exposing the peripheral roots. Thus, the outer roots are placed in contact with the soil of the planting site and growth commences almost immediately.
Under no circumstances should soil around the proposed planting site be removed to form a shallow basin for watering--to do so almost guarantees that the young mandarin tree will contract foot rot and die before its fifth year. In wetter, lower areas in southeast Texas, the use of raised beds is recommended. The soil in the planting site should be at least as high as the surrounding yard, if not higher. In addition, the tree should be set slightly higher than it was in the nursery container to assure that the budunion will remain well above the soil.
Mixing topsoil, compost, peat or other materials with the backfill soil is neither necessary nor desirable in good soils. Set the tree in the hole, backfill about halfway, then water sufficiently to settle the backfill around the lower roots. Finish backfilling the hole and then cover the root ball with about in inch of soil to seal the growing medium from direct contact with the air and thereby prevent rapid drying of the root ball.
To facilitate watering, bring soil from the garden or elsewhere to construct a watering ring atop the ground around the newly planted tree. The ring should be about two feet across and several inches high and thick. To water, just fill the water ring immediately after planting. After the water soaks in, it may be necessary to add a little soil to any holes formed as the soil settled around the roots.
The watering interval should be every few days for the first couple of weeks, then gradually increased to 7 to 10 days over the next couple of months. The watering ring will gradually melt into the surrounding soil, at which time the young mandarin tree can be considered to be established.
All weeds and lawngrass should be completely eliminated inside the watering ring, as the developing mandarin tree cannot compete well. A systemic, contact herbicide will work very well, so long as it is not allowed to contact the young tree leaves or green bark.
The best way to protect the young trunk from herbicide damage and, at the same time, to prevent sprouts along the trunk is to crimp an 8-inch by 18-inch piece of heavy duty aluminum foil around the trunk from the ground to the scaffold limbs. Fold the foil lengthwise, bring the long edges past the trunk on both sides, crimp the two edges together and lightly squeeze the foil around the trunk.
While mulching of citrus trees is commonly practiced in southeast Texas where there is an abundance of materials to use, mulching is not recommended for citrus because it increases the possibility of the tree contracting foot rot, for which there is no cure for home use. If you insist on mulching, keep the mulch at least a foot away from the trunk.
Fertilizer should be withheld until after growth commences. During the first year, a single cupful of ammonium sulfate (21-0-0) split into three or four applications is adequate. Use two cups in the second year and three in the third. Just scatter the fertilizer on the ground around the tree and water thoroughly. In areas other than the Valley, use whatever fertilizer analysis that is in general use in the area for trees and shrubs--simply adjust the rate based upon nitrogen content.
Cold protection measures for mandarin trees will be required sooner or later. Soil banks are very effective for young trees; the soil should be put up about Thanksgiving and left in place until early March. Exercise care when taking down the soil bank, as the bark underneath will be extremely tender.
Blankets, tarps or similar covers are also very effective and have the advantage of being quickly draped over the young tree. The corners should be stretched outward and tied down. More elaborate protection can be provided by erecting a frame structure of wood or PVC pipe over the tree to facilitate the use of plastic or large tarps during particularly severe cold weather. Supplemental heat can also be provided under the covers; incandescent bulbs and heat lamps are useful.
MATURE TREE CARE
Watering should be slow and thorough; probably every couple of weeks would suffice in any but the very sandy soils. Nutrition should continue at about one cup of ammonium sulfate per year of tree age annually in split applications in February, May and September, i.e. a 6-year-old tree should receive about six cups of 21-0-0 for the year. Adjust the rate for other fertilizers based upon the relative nitrogen content.
Lawngrass should be kept back about a foot from the canopy of the tree. Other than cold damage, no pruning should be necessary, as the mandarin tree will develop its natural shape without pruning. While mulching is not recommended for citrus trees, if you must mulch, keep the mulch at least one foot away from the tree trunk.
PRODUCTION, MATURITY AND USE
Mandarins are highly productive for the size of the tree, but most are subject to strong alternate bearing, which results in significant limb breakage during the heavy crop seasons (unless some means of limb support is provided). Because most mandarins do not store well on-tree after they reach maturity, production is generally greater than the average family can use during their relatively short season.
While the mandarins are noted for their bright peel color, it is not uncommon for the fruit to attain good eating quality before the peel loses its green color. In some cases, the flesh many become "ricey" by the time the peel achieves normal color--especially in those varieties which mature in September-November. Maturity is based on "eating quality" of the fruit--not on peel color.
Mandarins are primarily eaten fresh. However, in times of plenty, excess fruit can be sectioned and canned or frozen or it can be juiced and frozen.
Mandarins are afflicted with the same pests and diseases as other citrus, so the reader is referred to Home Fruit Production--Citrus, Table 2. One pest not discussed in the HFP-Citrus publication is Asian citrus leafminer, as the pest arrived in Texas about 1994. This leafminer attacks the new flushes of growth when the developing leaves are only about an inch long, leaving serpentine trails from their feeding and causing stunting and distortion of the leaf. Occasionally, trails or mines occur on fruit as well. Each growth flush is susceptible to attack and mandarins usually have four growth flushes annually. The spring flush is least damaged, since the leafminer does not overwinter well, but the later flushes can be devastated.
There are no chemical controls available for home use, although citrus spray oils do deter infestation if the application is timed to the development of a new flush of growth. Otherwise, it is best to try to ignore the damage; leafminer will not kill the tree and indiscriminate spraying kills a lot of the natural predators and parasites that help to keep leafminer populations down.
There are very few problems of mandarin trees that are life-threatening--and the home gardener cannot do anything about those anyway. Many of the rest of the insects and diseases that afflict mandarin can generally be ignored in the home garden, as blemishes to the peel affect only the appearance, and, in some cases, size of the fruit.
If one must spray, first identify the problem, then select the appropriate material and apply it properly and at the appropriate time to control the pest while minimizing damage to the complex of beneficial organisms that exist in citrus.
Alternate bearing is a problem that mandarin growers just learn to live with. In commercial orchards, heavy pruning during the "on-season" is sometimes used to reduce crop load--the home gardener would be better off removing some of the excess fruit soon after fruit set in the spring. Fertilizer rates should be increased by about one-fourth during the heavy crop seasons; similarly, fertilization should be reduced by about one-fourth during the light crop seasons.
Mandarin fruit tend to "plug" when pulled from the tree, i.e., a piece of the peel tears loose from the fruit and remains attached to the stem. Plugging is inconsequential for fruit that is to be used immediately upon harvest--but it is preferable to use hand pruning shears to clip the fruit from the tree to avoid damage. In clipping, the stem should be cut close to the fruit so as to preclude it from puncturing the rind of other fruit during harvest and handling.
Table 1. Characteristics of satsuma and tangerine varieties in Texas.
|Armstrong Early satsuma||Large||0-4||Red-orange||Lt-orange||Loose||Oct-Nov|
|Big Early satsuma||Large||0-4||Red-orange||Orange||Loose||Oct-Nov|
Table 2. Fruit classification, parentage and makeup of mandarin hybrids.1/
|1. Murcott||"Orange"||Unknown tangerine X unknown orange||50:0:50|
|2. Temple||"Orange"||Unknown tangerine X unknown orange||50:0:50|
|3. Orlando||Tangelo||Dancy tangerine X Duncan grapefruit||50:50:0|
|4. Minneola||Tangelo||Dancy tangerine X Duncan grapefruit||50:50:0|
|5. Thornton||Tangelo||Dancy tangerine X Duncan grapefruit||50:50:0|
|6. Robinson||"Tangerine"||Clementine tangerine X Orlando tangelo||75:25:0|
|7. Osceola||"Tangerine"||Clementine tangerine X Orlando tangelo||75:25:0|
|8. Nova||"Tangelo"||Clementine tangerine X Orlando tangelo||75:25:0|
|9. Lee||"Tangerine"||Clementine tangerine X Orlando tangelo||75:25:0|
|10. Bower||"Tangerine"||Clementine tangerine X Orlando tangelo||75:25:0|
|11. Fairchild||"Tangerine"||Clementine tangerine X Orlando tangelo||75:25:0|
|12. Page||"Orange"||Clementine tangerine X Minneola tangelo||75:25:0|
|13. Sunburst||"Tangerine"||Robinson "tangerine" X Osceola "tangerine"||75:25:0|
|14. Fallglo||"Tangerine"||Bower "tangerine" X Temple "orange"||62½:12½:25|
|(Clementine tangerine X Orlando Tangelo) X seedling orange||
1/ Tangor is a hybrid between tangerine and orange, Tangelo is a hybrid between tangerine and grapefruit while Tantangelo is a hybrid between tangerine and a tangelo hybrid.
2/ Quotations are used to denote the type of citrus which the respective hybrid most resembles and by which the industry usually refers to it.
Table 3. Characteristics of mandarin hybrids.
|1. Murcott "orange"||Medium||10-20||Yel-orange||Yellow||Tight||Jan-Mar|
|2. Temple "orange"||Medium||15-20||Red-orange||Orange||Moderate||Jan-Mar|
|6. Robinson "tangerine"4/||Medium||10-20||Yel-orange||Orange||Loose||Oct-Dec|
|7. Osceola "tangerine"5/||Medium||15-20||Red-orange||Orange||Moderate||Oct-Nov|
|8. Nova "tangelo"4/||Medium||0-30||Yel-orange||Orange||Slight||Nov-Dec|
|9. Lee "tangerine"||Medium||10-25||Yel-orange||Yellow||Tight||Nov-Dec|
|10. Bower "tangerine"||Large||25-40||Red-orange||Orange||Loose||Dec|
|11. Fairchild "tangerine"||Medium||20-30||Orange||Orange||Moderate||Oct-Nov|
|12. Page "orange"6/||Small||10-25||Orange||Orange||Tight||Oct-Feb|
|13. Sunburst "tangerine"7/||Medium||10-20||Red-orange||Orange||Loose||Nov-Dec|
|14. Fallglo "tangerine"||Large||20-40||Red-orange||Orange||Loose||Oct-Nov|
|15. Ambersweet "orange"||Medium||0-30||Yellow||Yellow||Moderate||Nov-Dec|
1/ Adherence refers to ease of peeling and to the ease with which fruit segments separate.
2/ Pollenizer required; use 2, 6, 7,8, 9, 12, or 13.
3/ Pollenizer required; use 2, 3, or 14.
4/ Pollenizer required; use 2, 3, 9, or 13.
5/ Pollenizer required; use 2, 3, 9, or 12.
6/ Pollenizer required; use 2, 3, or 9.
7/ Pollenizer required; use 2, 3, 4, 6, 9, or 14.
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