Oranges for Southern Arizona

¿Cómo se reparten el sol en el naranjo las naranjas? 
How do the oranges divide up sunlight in the orange tree? 
-Pablo Neruda – Chilean Poet

Sweet oranges (Citrus x sinensis (L.) Osbeck ) (Fig. 1) are the most popular citrus variety in the world and are mainly commercially harvested for juice – 75% − rather than for fresh eating − 25%. There is nothing quite like peeling and eating a fruit from one’s own orange tree on a cool winter morning in the desert or enjoying a fresh-squeezed glass of orange juice that is far better than anything one can purchase at the supermarket. Sour oranges (Citrus x aurantium) and their subspecies are most often used as ornamental trees since their fruit are not often eaten fresh due to extreme bitterness. Sour orange oil is found in perfume and its peel is the preferred ingredient in marmalade. Whether you prefer sweet oranges or sour ones, choosing the proper variety is the most important first step.

Both sweet and sour oranges are complex naturally occurring hybrids of mandarins and pummelos (a large fruit that is also an ancestor of grapefruit) that originated in Southeast Asia, southern China and Eastern India thousands of years ago.1 Over the centuries, oranges have naturally mutated into hundreds of varieties which farmers have selected and propagated. However, only a few varieties are available at a local retail nursery. Descriptions of the most commonly available sweet and sour orange varieties available from retail nurseries in Arizona (plus a few extra of interest to the author) and their characteristics are found below. These descriptions are specific for the Arizona desert and may be slightly different than those found in other publications. The descriptions do not include those for “mandarin oranges”, which are more properly called mandarins and will be described in a subsequent publication. Primary harvest periods for the orange varieties mentioned are found in Table 1.

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Sweet orange varieties can be categorized into five groups − navel, sweet (Common), ‘Valencia’, blood and acidless. In Arizona, there is always an orange variety that is ready to eat from late October through late May. Early maturing oranges often have fully colored interiors and are sweet enough to eat before they have full exterior color, particularly if the fall is warmer than usual. Late in the season, some oranges may become insipid, while other late-maturing varieties will lose their exterior orange color and revert to green due to springtime heat. It always is best to taste an orange to determine if it is ready to eat rather than relying on exterior color.

The navel orange variety originated as a naturally occurring mutation of a sweet orange. Navel oranges develop a rudimentary secondary fruit at the base of the primary fruit, opposite the stem end, which is enveloped within the peel. This mutation also causes the fruit to become seedless because the trees have no functional pollen and few viable ovules². Navel oranges need no pollen to set fruit (See the “Special Considerations…” section below).

Navel oranges are favorites for eating fresh because they are usually seedless and relatively easy to peel. They can be juiced, but the juice should be consumed directly because most navel orange juice contains bitter compounds including limonin, which make stored juice disagreeable. A drawback of growing most navel orange trees in Arizona is their sensitivity to heat. The tree will normally drop many of the small fruits in late spring, and this problem is made worse if the tree is under water stress or if the temperatures during bloom or fruit set in April and May are abnormally hot.

Navel orange fruit, especially the late-harvested selections, also will become dry or granulated if planted on a vigorous rootstock, such as Citrus macrophylla or Citrus volkameriana. Granulation can also be a problem if navel orange trees are fertilized with too much nitrogen especially late in the season. Granulation is worse where there are sandy or gravelly soils. It is always better to complete all fertilization of navel oranges before July 1st if granulation is a problem. In Southern Arizona, both quality and quantity of navel orange fruit can disappoint unless the tree is cared for properly.

‘Atwood’ originated as a naturally occurring mutation of ‘Washington’ in 1935 and is very similar to the parent variety. It gained attention because it matures slightly earlier and its rind is smoother than ‘Washington’, and it stores well on the tree. Early-season fruit quality, however, is not quite as good as ‘Washington’, meaning that it will be slightly less sweet³. It has been extensively planted in California.

This selection of navel orange is new to the United States but is well-known in Brazil where it originated as a bud sport (spontaneous mutation) of the ‘Bahia’ in 1907. Reports indicate that it is smaller and less vigorous than the ‘Bahia’, but more productive⁴ and less likely to produce overly large fruit. Also, it is said to mature one to two weeks earlier than ‘Bahia’ and better adapted to hotter climates because it produces more consistently. Finally, ‘Bahianinha’ is known in Brazil to have a richer and sweeter flavor than ‘Bahia’, a fact that the author can confirm, based on limited consumption. Currently there are just a few bearing trees at the University of Arizona in Yuma, but the selection is being propagated.

‘Chet Hoel’, a local navel selection, originated as a bud sport of ‘Washington’ in Mesa, Arizona in the early half of the 1900’s. It is named after one of the founders of Consolidated Citrus Growers, a citrus growing, packaging and shipping business. ‘Chet Hoel’ is similar to ‘Washington’ in tree size and harvest time. However, reports indicate that it has lower acidity and peels easier than ‘Washington’⁶.

The ‘Don Shaw’ navel orange is another local selection that originated as a natural mutation of ‘Washington’ near Mesa, AZ and is named after a local citrus grower. According to reports, the tree size of this selection is smaller than ‘Washington’ it holds fruit well later into the spring and when juiced, the flavor is less bitter⁷.

‘Fisher’ originated as a naturally occurring mutation of ‘Washington’⁸. This selection gained attention because it becomes sweet earlier than ‘Washington’, but it does not color earlier. Tree characteristics are similar to ‘Washington’. In navel orange trials conducted at Yuma and Phoenix, ‘Fisher’ had the greatest yield.

‘Lane Late’ was the first of many late-season navels originating as bud sports of ‘Washington’ in Australia. Although these are often called summer navels, they can be harvested beginning in January in the low desert and may be harvested through April. Fruit granulation can be a problem with ‘Lane Late’. There are approximately thirteen different varieties of late navels with the ‘Lane Late’ being one of the most promising in Arizona trials. Other varieties include the Australian selections ‘Autumn Gold’, ‘Barnsfield’, ‘Chislett’, and ‘Powell’ and the Spanish selection ‘Navelate’. Tree characteristics are indistinguishable from ‘Washington’.

‘Newhall’ is an early-maturing selection from California that originated as a bud sport of ‘Washington’¹⁰. This selection can be harvested as early as late October and has a deeper rind and flesh color than fruit of ‘Washington’, but the trees are less vigorous with darker leaves¹¹. Other tree characteristics are similar to ‘Washington’.

This selection, like all the other navel oranges, originated as a spontaneous mutation of ‘Washington’. ‘Robertson’ was discovered in California in 1925 and distinguishes itself because the tree lacks vigor (dwarfing) and is heat-resistant, precocious and very prolific¹². Fruit mature 10 days to two weeks before ’Washington’, but are slightly smaller. Fruit flavor is similar to ‘Washington’.

Sweet oranges or “Arizona Sweets,” are terms commonly used to refer to a group of orange varieties that are harvested from early November through February in Arizona. The author recalls being told that the “Arizona Sweet” term appeared in the first half of the 20th century, Arizona growers produced several sweet orange selections, but they were indistinguishable from each other. Therefore, rather than selling them in boxes under their individual names, the packinghouse sold them all under the term “Arizona Sweet”. When trees in the nursery are identified only as ”Arizona Sweet“ they are usually either ‘Hamlin’, ‘Trovita’ or ‘Salustiana’.

Unlike navel oranges, sweet oranges are versatile, they are good for both juicing and eating fresh. Unlike navel oranges, sweet oranges can be seedy, and do not have the secondary fruit. Sweet oranges are not as easy to peel as navel oranges but peel easier than ‘Valencia’ oranges. Most sweet oranges mature earlier than ‘Valencia’ oranges. Early maturing sweet oranges may develop granulation, especially in those years when it is especially hot in the fall, when fertilized with too much nitrogen, or when grown on sandy soils. Tree characteristics of sweet oranges are similar to those of navel oranges.

‘Diller’ originated in Phoenix, Arizona in 1910, and is a small to medium fruit with comparatively few seeds^13,14. This variety is notable due to its productivity and is excellent for juicing. Fruit are ripe from December until February and are slightly smaller than fruit of other sweet oranges. ‘Diller’ fruit retain some “tartness”.

Macetera’ is an old Spanish selection¹⁶. Trees are large and the selection has regular high yields once mature. Fruit are late-maturing for a sweet orange, bearing from January until the end of April, similar to a ‘Valencia’. However, the peel is thin and may be easily removed unlike a ‘Valencia’. Because of its thin peel and late maturity, ‘Macetera’ fruit are sensitive to frost. The juice content of the fruit is high, seediness is moderate, and the flavor and fragrance are unique.

‘Marrs’, also known as ‘Marrs Early’, is another early-season, sweet orange that originated in 1927 in Texas as a bud mutation of a navel orange tree¹⁷. However, ‘Marrs’ fruit do not have a navel. Trees are compact but moderately vigorous, precocious and prolific. The fruit is medium to large in size and has seven to ten seeds per fruit. Fruit reach edibility, because they are low acid, in late October but they are best when allowed to remain on the tree for at least 2 to 4 more weeks. Fruits have thin light orange peels and seven to ten seeds each. ‘Marrs’ fruit will become insipid if left on the tree too long.

The ‘Salustiana’ orange originated as a bud mutation from another sweet orange in Spain in 1950. This variety is not planted commercially in the United States but is commonly planted in Mexico¹⁹. ‘Salustiana’ trees are vigorous and productive²⁰. Fruit are mid-season, ripe from December until February or March and are virtually seedless. Fruit size is medium to large. The flesh has a fine, rich, sweet flavor, and is melting, meaning that it softens rapidly in the mouth when eaten.

‘Trovita’ is another high-quality sweet orange that originated as a seedling from a fallen ‘Washington’ navel orange fruit in California in 1916²¹. The tree is vigorous and upright with a slight tendency to alternate bear²². This variety is considered to be heat tolerant and productive under desert conditions. Compared with ‘Washington’, the fruit is smaller, juicier, and of milder flavor. ‘Trovita’ fruit do not have a navel and their juice will not become bitter.

‘Valencia’ oranges are the leading citrus variety in many citrus-producing countries around the world. Although they can be eaten fresh, ‘Valencia’ oranges are most often processed because of their excellent quality juice which has a deep orange color, high sugar content and an unparalleled richness of flavor. This is the primary fruit processed in Florida for juice.

While the name would suggest that the origin of the ‘Valencia’ is the eponymous Spanish city, in reality the origin is likely China, where several similar selections exist²³. One of these selections was likely taken to Portugal and then to the Azores where it was first mentioned²⁴. From the Azores, it can be traced to England in 1865 where it was named ‘Excelsior’ and it travelled onward to the United States. The variety was first planted in California in 1876 and was likely established in Arizona soon thereafter.

‘Valencia’ fruit have a high heat requirement for maturation. In the desert, that requirement is met just a few weeks before bloom; there are about 11 months from bloom to maturity. In cooler, coastal areas, the requirement may not be met until 14 to 18 months after bloom. Therefore, the typical ‘Valencia’ fruit from the desert garden will be harvestable in February, whereas the ‘Valencia’ fruit in the supermarket, which comes from cooler areas of California, will not be available until June after the earlier-maturing navel oranges have been harvested. ‘Valencia’ fruit also hold well on the tree and can be harvested into May or June in the desert. ‘Valencia’ fruit become sweeter later into the harvest season, and the fruit has a lower level of bitter compounds at harvest compared with navel oranges²⁵. In the latter part of the season, the orange color of the peel will degrade, and the green color will reappear, a condition known as “regreening.” However, the flesh does not quickly lose its color or flavor even when the exterior is green. ‘Valencia’ fruit is medium in size with few seeds, typically zero to six. ‘Valencia’ is a welcome orange that can be picked from the tree in the late spring and early summer when all the others are no longer available.

There are several selections of ‘Valencia’ oranges that have been noteworthy enough to have been given separate names. A ‘Valencia’ tree purchased at the nursery without additional identification is likely one of these noted below. All of them perform well in the desert.

‘Campbell’ is often called a ‘Valencia’ because its fruit is indistinguishable from that selection, however it was planted as a seedling in 1871, five years before the introduction of ‘Valencia’ to California²⁶. This selection is purportedly vigorous and a little slower to come into bearing than a ‘Valencia’ and may regreen faster in the desert.

‘Olinda’ was found as a chance seedling in California in 1939²⁹. Tree and fruit of this selection are indistinguishable from other ‘Valencia’ selections. ‘Olinda’ is the most common ‘Valencia’ grown commercially in Arizona.29. Tree and fruit of this selection are indistinguishable from other ‘Valencia’ selections. ‘Olinda’ is the most common ‘Valencia’ grown commercially in Arizona.

These oranges are characterized by the dark red color that develops internally and sometimes externally, hence the common name “blood orange”. The pigmentation is caused by anthocyanin pigments, rather than the red or pink lycopene pigments found in the ‘Cara Cara’ navel orange and in grapefruit. Expression of the anthocyanin is regulated by genes that are induced by cold temperatures³⁰.

In Arizona, blood orange color develops best after a hot dry summer followed by a cold winter. Coloration may be slight in December, but as the winter progresses, color will usually increase. Maximum pigmentation will appear by February. However, in the warmer areas of the Sonoran Desert many blood oranges fail to achieve this typical color every year because there is not sufficient cold. Blood oranges grown in cooler-winter areas of the state such as Tucson will have the most coloration, while those grown in warmer-winter areas such as Yuma will have the least. Fruit exposed to the sun will have more interior color than those in the shady part of the tree, and appearance of red color on the peel is no guarantee of red color inside.

This selection was introduced from an unknown Mediterranean country to Florida about 1880 and was subsequently brought to California and Arizona³². Its color development is rather inconsistent but is purportedly better in the desert than on the coast. Flesh is streaked with color. ‘Ruby’ flesh is tender and juicy, and the flavor is rich.

Acidless oranges are not well-known in the United States, but are quite popular in Europe, North Africa and Brazil. They have extremely low acid levels. The author was unable to find any acidless varieties for sale in Arizona nurseries, but includes it in this publication in hopes of increasing interest in the selection.

Also known as the bitter orange, the sour orange and its variants are primarily found in the landscape as ornamental trees rather than for consumption due to their unpalatable fruit. Sour oranges are also used as a rootstock, except where Citrus Tristeza Virus (CTV) is present, and for marmalade. Fruit of trees related to sour orange are sometimes candied or used for perfumes and rind oil.

Information on how to grow citrus in Arizona, including irrigation, fertilization, propagation, frost protection common citrus problems, diseases and insects can be found using the search engine at https://extension.arizona. edu/pubs. However, there are certain horticultural considerations that if noted, will make growing an orange tree more successful.

All oranges other than sour orange trees are grown on a rootstock. A rootstock is another citrus variety that the orange tree is grafted to in the nursery. Orange trees are grafted to rootstocks because the rootstock generally improves growth, fruit quality or disease resistance of the tree. If you look carefully at the trunk, you will often see an area where the bark changes texture or where the trunk increases in circumference. Below that area is the rootstock and above it is the orange tree.

Choosing the proper rootstock is vital when growing oranges in the desert, but it is often difficult to know which one is used. Sometimes the rootstock name is found on a tag tied to the branch or wrapped around the trunk. Occasionally it is found on a sticker on the pot. The best rootstocks for oranges in Arizona (in no particular order) are as follows: Sour orange, Smooth Flat Seville, Carrizo Citrange and C-35 Citrange. Flying Dragon (a dwarfing rootstock) and Trifoliate orange seem to be more suitable in heavy clay or silt soil, rather than in sandy or gravelly soils unless amended with organic matter. The author does not recommend purchasing orange trees on Volkameriana or Macrophylla rootstocks, as these will produce vigorous trees but with serious problems with granulation (see below).

Navel oranges and ‘Valencia’ oranges can set fruit without the need for pollination. This may be true of other orange varieties as well. Therefore, it is not necessary to plant two varieties of orange. However, even if pollination was needed, there are usually many varieties of citrus in a neighborhood that would provide pollen if needed.

Navel oranges, and to a lesser extent early maturing sweet oranges are known to drop flowers and fruit when under heat stress in the spring. Temperatures in the 90’s (F) or greater during bloom or fruit set will lead to excessive fruit drop leading to an unacceptable reduction in the final crop. While there is no way to eliminate this problem entirely, adequate irrigation is key. Sufficient irrigation will reduce the degree of fruit drop while insufficient irrigation in the spring will make it worse.

The exterior color of an orange does not necessarily indicate interior maturity, particularly when the fall is warmer than normal. Oranges turn color from green to orange because of biochemical reactions that are triggered by temperature. The sooner it becomes cool, the sooner the color change from green to orange. But the change from sour to sweet in the interior of the fruit is determined by heat. The more heat in the fall, the quicker the acids in the fruit are reduced and the sugars increased. Therefore, when the fall is warmer than usual the fruit might have a greenish exterior but be perfectly ready to eat. The best way to tell if an orange is ripe is to taste it!

Figures 1, 18 – Glenn C. Wright

Figures 2-17 – Toni Siebert and David Karp, University of California-Riverside Citrus Variety Collection.

Figure. 19 – Orange_marmalade-3.jpg .by jules is licensed under CC BY 2.0.

Figure. 20 - https://www.flickr.com/photos/ giveawayboy/2145248676 by giveawayboy is licensed under CC BY 2.0.

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³⁰ Solved: The mystery of the blood orange, AAAS Eureka Alert, accessed June 10, 2020. https://www.eurekalert. org/pub_releases/2012-03/asop-stm031612.php

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³⁸ USDA, Agricultural Research Service, National Plant Germplasm System. 2020. Germplasm Resources Information Network (GRIN-Taxonomy).National Germplasm Resources Laboratory, Beltsville, Maryland. URL: Accessed June 30, 2020. https://npgsweb.ars-grin.gov/gringlobal/taxonomydetail.aspx?id=490141.

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