What makes oranges sweet

Patrice Hanlon answers your gardening questions every other week.

Dear Garden Coach: I have a lemon tree and two types of orange trees. The trees are prolific, but my oranges are very sour. Is there something I can do to make them sweeter?

One is a Valencia and the other is a navel. The trees are covered with oranges, and they will soon bloom with more. How do I know when they’re ripe?

Lynda M.


Dear Lynda: There is nothing more disappointing than having a beautiful orange to eat, only to find that it is quite sour. Sometimes we are eager to pick the fruit when it has matured on the tree, but there is a difference between a fruit being ripe and mature.

A mature fruit is one that has completed its growth phase. Ripening involves the changes that occur within the fruit after it is mature, which is really the beginning of decay. These changes usually involve starches converting to sugars, a decrease in acids and a softening and change in the fruit’s color.

One way to know when the fruit is ripe and ready to harvest is that there should be little resistance when you pull it off the tree. If the fruit resists, then it’s telling you it needs to hang on a little longer to ripen.

Timing is important as each variety has a different time for harvesting. Navel oranges ripen in the winter and into the spring and early summer, while Valencia oranges begin ripening in the spring and are harvested through the summer.

Soil health is critical for all plants in the garden. Citrus will tolerate lots of different soils, but drainage is important. Adding organic amendments is the best and easiest way to improve your soil, and you have the added benefit of the tree getting more nutrients as the compost further decomposes. Established trees will benefit from top dressing with compost every year.

Top dressing is simply adding a layer of 2 to 3 inches of compost to the drip line of the tree. Be sure to keep the compost away from the trunk of the tree to reduce the potential for crown rot and to reduce places for pests to hide in.

Lastly, how are you fertilizing your tree? Citrus plants are heavy feeders and like lots of nitrogen. Yellowing leaves indicate lack of fertilizer or poor drainage. Citrus also is sensitive to salts in the soil, which can occur from your water. If you haven’t tested your soil, it is always a good thing to do.

When choosing a fertilizer, I prefer organic brands such Dr. Earth Citrus, but there are others that might work better for you. Look for brands that are slow-release and contain trace minerals such as iron, zinc, and manganese. Slow-release fertilizers are best since they feed the tree over a longer period of time and are better for the environment as they don’t run off into the storm drains, which could jeopardize the overall health of our water. Be sure to read the information about the rates of applications.

Finally, check the base of your tree. Failing to remove suckers from below the graft can encourage the tree to begin producing fruit from the rootstock. Some rootstocks for sweet oranges include sour oranges and lemon trees.

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Advice from the Help Desk of the
Master Gardeners of Contra Costa County
Washington Navel Orange
Photo: Launa Herrmann
Solano County MG
Client: I have a moderate sized, probably 8-10 year old orange tree in my garden that was here when we bought the house. While it is producing what looks to be mature fruit, when they are peeled and eaten, they are not as sweet as I expect. What could I do to improve the sweetness of the oranges?

MGCC Help Desk: Thank you for contacting Master Gardeners help desk with your question about growing sweeter oranges.
The fruits from sweet orange trees in your garden may not taste as sweet as supermarket oranges. Many factors affect the flavor of ripe oranges: the climate, when they are harvested, the variety, pruning, cultural care (e.g., mulching), fertilizing, and irrigation. Without knowing what specific type of orange tree it is, it is difficult to know if you actually have a tree that does produce sweet fruit, but we will assume that it is a sweet orange tree in your yard.
Here are some reasons that the fruit may not be as sweet as you would like it to be along with some possible remedies:
Lack of Heat – The amount of heat the garden receives in summer determines whether or not oranges taste sweet at harvest time. Many orange tree varieties need heat to sweeten their fruits, and if they are grown in an area with a mild climate, you may get oranges that are more sour than sweet. Summer heat builds sugar in the fruits. Navel oranges need a lot of heat to develop their signature sweet flavor.
Harvest Too Early – Letting the oranges stay on the trees longer in winter helps to lower their acid content during the cooler winter temperatures. If oranges are picked without taste testing them first, they may taste too acidic or sour for your liking. Solve that problem by sampling a single orange from the trees for flavor before harvesting the rest because oranges do not sweeten any more once they are picked.
Sour Orange Variety – Your orange tree may not produce sweet oranges. Your tree could be a sour orange tree instead of sweet orange tree. Sour orange tree fruits are grown for their bitter peels, which are used to add orange flavor to recipes. Their flesh is exceptionally sour and acidic. Sour orange peels have a dimpled appearance and a slightly reddish cast. If you don’t want to remove a sour orange trees, you could use their fruits to make marmalade or jellies.
Rootstock Takeover – Failing to remove suckers from below the graft on an orange tree encourages growth of the rootstock to the point it takes over the scion and produces flowers and fruits of its own. The fruits from the rootstock are not usually the same flavor as fruits from the scion, depending on the rootstock. Some rootstocks compatible with sweet orange trees include sour orange trees and various lemon trees. If those rootstocks produce fruits, they will have the bitter, sour flavor of a sour orange or lemon instead of the sweetness of a sweet orange. You may be able to tell if the rootstock has taken over by considering the following:

If this tree is grafted (and most orange trees are), and if it was grafted on dwarfing or semi-dwarfing rootstock, they are frequently grafted to trifoliate rootstock, so that can make the diagnosis much easier. If you see any leaves in groupings of 3, it is likely that it is rootstock, as orange leaves are singly produced on a branch. Also, the leave size and shape will be different and the stems may have large thorns. If the rootstock has taken over, you can attempt to prune the rootstock off if there is anything left of the original grafted tree.

Fertilizing: Citrus do require adequate and regular fertilization to maintain their growth and satisfactory fruit production. Here is a UC link to additional information on citrus fertilization for the home garden: http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html

Citrus Culture in Contra Costa County: Finally, in summary of the above, here is a link to an excellent overall MG article about care of citrus in our area. This article will help you to make sure that you are using the right fertilizer and giving the tree the right amount of moisture for optimum quality fruit production in additional to other helpful suggestions for citrus success:

Please let us know if we can be of further assistance.
Help Desk of the Master Gardeners of Contra Costa County

Note: The Master Gardeners of Contra Costa’s Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we’re open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: [email protected], or on the web at http://ccmg.ucanr.edu/Ask_Us/

Citrus Care

SERIES 19 | Episode 18

When it comes to giving citrus trees tender loving care there are a few basic principles – and one of the most important is adequate nutrition.

Citrus trees are gross feeders – that means they need to be fed in July, November and March with a good citrus and fruit tree fertiliser. Give them 125 grams for every year of the tree’s age at each of the applications. But when the tree gets to about 10 years old or older it needs 1 1/4 kg of fertiliser. Spread the fertiliser evenly around the drip zone, water in and the tree will power away.

Even with regular fertilising the leaves might still show symptoms of iron deficiency. This is evident when the leaf veins stand out dark green and the tissue between turns a pale green, yellow or even white. To correct this and other deficiencies, add trace element mixture around the base of tree.

If the fruits are sour there is a simple way to sweeten them. Sprinkle about six handfuls of sulphate of potash around the tree and then water in with two teaspoons of Epsom salts mixed into10 litres of water.

There are a few pests that attack citrus and one of the most common is the citrus leaf miner. It’s not life threatening, but it will reduce the yield. Look out for silvery trails in the leaf – that’s made by the miner and it distorts the leaf. Spraying with a white oil preparation will soon control that.

Any black discolouration on the leaf is a black sooty mould. It’s always associated with one or other of the so called sucking insects. These could be mealy bugs, which are small, white, furry looking insects and that are sticky to touch. It could also be scale or aphids. Spraying with white oil or a soft systemic insecticide will usually bowl these off.

One of the best known pests is fruit fly, which ruins the fruit. To get something to control this, go to your local nursery and get an organic fruit fly control.

Another citrus pest is citrus gall wasp. The insect lays its egg in the branch, which swells so the hatching insect can get food. Prune the gall out and get rid of it before September when the adult hatches.

Citrus trees are great in the garden. They look fabulous and provide wonderful fruit. Grow them in pots, in courtyards or in smallish orchards. If you follow the simple rules of fertilising, watering and tender loving care, they’ll reward you, with plenty of beautiful fruit.

Sour orange

Oranges can be divided into two broad categories: sweet oranges and bitter oranges.

Sweet oranges have a sweet and juicy flesh and are found in both savory and sweet dishes. They are eaten out of hand, as a breakfast fruit, snack, or dessert. They can be sectioned and served in fruit salads or compotes, chicken or turkey salads, or as a topping for tarts. The grated rind or juice of sweet oranges is used to flavor soufflés, sauces, glazes or creams, mousses, and sorbets.

Bitter or sour oranges have a dry flesh that is too bitter for eating for eating out of hand. But the peel of the bitter orange is aromatic and flavorful and can be used to makes marmalades, candies, sauces, syrups and liqueurs.

The sweet oranges’ distinctive flavor is a blend of sugar and acid. Sweet oranges are round to oval in shape and can be further divided into three groups: navel, common, and blood oranges.

The bitter orange is said to be an ancestor of the sweet orange. Bitter oranges are not for eating out of hand.

Sweet oranges–navel, common, and blood–and bitter oranges:

• Navel oranges have thick, rough, bright orange skins that are easy to peel. They are large and seedless with a rich, juicy flavor, and their segments are easy to separate. Sweet oranges develop a small second fruit within the larger fruit at the blossom end of the orange. Where the second fruit develops is an indentation that looks like a human navel and thus the name. The Washington navel orange is the original and best known navel orange. Other navel orange varieties are Cara Cara, Fukumoto, Lane Late, Robertson, Skaggs Bonanza, and Spring. The peak harvest for navel oranges is from mid-winter through early spring.

• Common oranges are round or slightly oval and medium-sized with a thin, smooth rind. They have a sweet-acid flavor and are juicier than navel oranges. Common oranges also have more seeds and are more difficult to peel than navel oranges. Common oranges are sold fresh for eating out of hand, but more importantly almost all orange juice is squeezed from common oranges. The Valencia orange—the most popular orange in the world—is a common orange. Other common orange varieties include Trovita, Hamlin, Jaffa, Marrs, Parson Brown, and Pineapple. The peak harvest for common oranges is from late spring to mid summer.

Blood orange

• Blood oranges are similar in size to common oranges but with a red blush skin and a streaked to full scarlet, crimson, or purple flesh. The blood orange is juicy and has a sweet-tart taste that is rich, flavorful and often hints of berry. Blood oranges are popular for eating out of hand, juicing, and as garnishes for sweet and savory dishes.The best known blood orange varieties are Sanguinello, Moro, and Tarocco. The peak harvest for blood oranges is from early winter to early spring.

• Bitter or sour oranges usually have a thick, dimpled, deep-orange colored peel, and a sometimes pithy flesh. Bitter oranges are usually not eaten fresh because the flesh is too tart and bitter tasting. The sour flavor of these oranges is a result of the fruits’ acidic juices; the bitter is due to its essential oils. The peel and juice of sour oranges are used to make marmalades, candies, sauces, syrups, pies, flavorings, and liqueurs. The best known sour oranges are Seville, Bouquet de Fleurs (also called Bouquet), Chinotto, and Bergamot. Sour oranges are harvested beginning in late fall and the harvest continues through spring depending upon the region and climate.

Sour oranges are higher in natural pectin—a gelling agent—than sweet oranges. That makes them ideal for use in marmalades, jellies, and preserves.

The botanical name for the sweet orange is Citrus sinensis. The botanical name for the bitter orange is Citrus aurantium.

Bigger isn’t always necessarily better when it comes to fruits. Bite-sized fruits can also offer interesting flavors! One such fruit is the delightfully contradictory fruit, the kumquat.

What are Kumquats?

Kumquats are a type of small citrus fruit that originates from South Asia. Its trees bear oval-shaped fruits that are comparable in size to large olives. Its Chinese name roughly translates as “golden orange.” Standard sized trees can grow between 8 to 15 feet high, but you can find dwarf kumquat trees for sale in nurseries that come in more manageable sizes. Kumquat tree leaves have a dark glossy green color, while the flowers are white, similar to its other citrus cousins. It is generally in season from November to March and can produce hundreds or even thousands of fruit every year, depending on the size of the tree.

What makes it different?

While it shares similarities to the orange, looking like a smaller, oval-shaped version of its citrus cousin, kumquats offer a different eating experience. Oranges are typically eaten out of hand by peeling off the rind to get to the sweet and juicy flesh. For Kumquats, you eat it whole. Its peel is the sweetest part of the fruit while the fleshy part is sour. If you’re not a fan of the tangy taste of the fleshy part, you can nibble on one end of the fruit and squeeze off its juice and seeds and you’re left with the delightfully sweet rind.

Which kind of kumquat tree should I get?

If you’re sold on the idea of growing a kumquat tree but not sure which kind to get, then there are 2 varieties we can recommend to you. It depends on how you plan to use the fruits. For cooking and making jams, you should ask your preferred nursery if they have Nagami kumquat trees for sale. Nagami kumquats, or Fortunella margarita, are the more commonly grown type of kumquats and produce oval-shaped fruits. It’s comparatively larger in tree and leaf size to other kumquat varieties and is also known as a sour kumquat. This is a cold-hardy tree that needs full sunlight to thrive and generally flowers in the summer and fruits around winter.

For eating out of hand, you may want to look into getting a sweet kumquat tree. Meiwa kumquats, or Fortunella crassifiola, have a rounder fruit that has a lower seed content. Some fruits are entirely seedless making it great for munching on directly. It has a thicker rind compared to nagami kumquats, making it comparatively sweeter.

Both types of kumquat trees are semi-dormant during winter, making them quite cold-hardy, though Nagamis are slightly more so. Kumquat tree care is fairly straight forward. They require full sun to thrive. Make sure to keep the soil moist around the young trees, but not to the extent of making it soggy. Pay particular attention to it during dry seasons to ensure its health. You can use a layer of mulch to help water retention but make sure to pull any mulch back several inches from the tree base, to avoid root rot.

What Does Orange Vanilla Coke Taste Like? Coke’s First New Flavor Has Creamsicle Vibes

On Feb. 8, Coca-Cola announced something huge: Orange Vanilla Coke is on the way — and it’s arriving a lot sooner than you might think. The brand-new cola flavor will hit shelves on Feb. 25, just in time for the fast-approaching arrival of spring. And hey, guess what? For those who might be wondering exactly what Orange Vanilla Coke tastes like, good news: Coca-Cola kindly granted me the opportunity to try it, so I’ll do my best to answer whatever questions you might have.

Orange Vanilla Coke made waves when it was announced for one big reason: It’s reportedly the first new Coke flavor to arrive in over a decade. But wait, I hear you ask — a full decade? Really? What about, say, those wacky fruit flavors that joined the lineup last year and just got an expansion in January? You know, that Blueberry Acai and Strawberry Guava stuff? Aren’t those new flavors, too?

I mean, yes, they are — but they’re specific to Diet Coke. Similarly, the Georgia Peach and California Raspberry flavors that launched in 2018 are a line all their own — Origins — rather than part of the regular Coke and Coke Zero Sugar flavor lineup. The only permanent flavors available in the standard Coke/Coke Zero Sugar line up until now have been Cherry, which was introduced in 1985, and Vanilla, which had its original run from 2002 to 2005 before being relaunched in 2007.

Courtesy of Coca-Cola

But now, Orange Vanilla Coke has joined the Coke and Coke Zero Sugar ranks — and it looks like it’s planning on sticking around. It doesn’t hit shelves until the end of the month; however, I was lucky enough to get the chance to taste the new flavor in advance of its official arrival, so if you’re wondering what the stuff actually tastes like, I might be able to help you out with that.

In its canned form, Orange Vanilla Coke utilizes the same design that the standard Coke line has used since 2016: The logo is large, the center of the can is red, and an arc of a contrasting color — in this case, orange (naturally) — frames the outside edge. The soda itself also looks like you’d expect Coke to look — fizzy and a warm, caramel-brown color. It doesn’t have a wildly different smell than other Cokes do.

The flavor, though? That’s certainly different. And hey, guess what? If you, like me, heard the phrase “Orange Vanilla Coke” and thought, “That sounds kind of like a Coke-flavored Creamsicle”… you’d be absolutely right.


It does taste like a Creamsicle — but not like, say, Stewart’s Orange ‘N Cream soda does. Rather, Orange Vanilla Coke tastes like a cola-spiked Creamsicle. Like, if you poured yourself a glass of Coke, stuck a Creamsicle in it upside-down, let it melt a bit, and then either A) took the Creamsicle back out and ate it, B) drank the Coke now mixed with melted Creamsicle, or C) both? That is exactly what Orange Vanilla Coke drinking this stuff is like. What’s more, the combination of cola and Creamsicle isn’t as weird as it might sound; because of the vanilla, it actually works. Think of it like a Coke float, just with something like orange sherbet instead of a more “standard” ice cream flavor.

“We wanted to bring back positive memories of carefree summer days,” Coca-Cola brand director Kate Carpenter said of the new flavor in a press release. “That’s why we leaned into the orange-vanilla flavor combination — which is reminiscent of the creamy orange popsicles we grew up loving, but in a classically Coke way.” I think it’s safe to say that they’ve reached that goal; given that both my initial impulse and deeper assessment hinged on comparing the drink to liquid Creamsicles… mission accomplished.


Will Orange Vanilla Coke be your jam? Only you can answer that question. It is quite sweet, even for a soda, so if you’re not a fan of sweet drinks, or only like them in very small doses, you might not be rushing to try this one; similarly, if you just, y’know, aren’t an orange and/or vanilla kind of person, you’ll probably want to skip Orange Vanilla Coke. But if you, like Kate Carpenter, grew up as a devotee of creamy orange popsicles, give this one a shot when it hits shelves; it’ll be perfect for picnics when the weather starts to warm up, and until then, it can remind you of the brighter, fruit-filled days to come as we see out the last of winter’s gloom.

Orange Vanilla Coke will be available nationwide in 12-ounce cans and 20-ounce bottles starting on Feb. 25. Orange Vanilla Coke Zero Sugar will debut in the same two formats in March, although it will only be around for a limited time through May. For the curious, a 12-ounce can of Orange Vanilla Coke contain 34 mg of caffeine.

Find out more here. Cheers!

Q: I have a young orange tree that looks healthy. It made its first fruits this year and they are nice and orange but sour. Did I get a bad tree?

A: You did not necessarily get a bad tree. I get this question in many forms from all areas of the Southland, so I will answer in a more general way. There are several causes of sour citrus fruits that could be the explanation. The most obvious possibility is that you are picking the fruit too soon. Citrus fruits, whether they are oranges, mandarins, or other citrus species, may develop their mature color long before the fruits are ready to harvest.

For example, Valencia oranges turn a bright orange color by January because of the colder winter weather. However, rind color is not an indication of internal maturity. Valencia oranges are not mature and sweet until April, regardless of rind color. It helps to know the expected season of maturity for your citrus variety.

Although commercial growers are able to determine harvest date by analyzing their crop for a desirable balance of sugar to acid, the home gardener must rely upon what amounts to a “pick one and taste it” method. If it’s sour, wait two weeks and try again. You may have to repeat this taste-testing a number of times before arriving at the ideal time for harvest.

Another possibility is that the tree is not receiving enough heat during the summer. This is especially a problem in coastal areas or higher elevations. Citrus requires high heat to develop sugars in the fruit. If you live in a cool area you can concentrate heat by planting oranges and mandarins beside a south-facing block wall or building. Except for ‘Oroblanco’ and ‘Melogold’, which are pomelo-grapefruit hybrids that are naturally very low in acidity, grapefruit will usually not produce satisfactorily sweet fruit in cool locations no matter what you do.

The final possibility is that the fruiting wood is sour orange or some other sour-flavored rootstock. Citrus trees are budded or grafted onto more vigorous rootstock varieties that have unpleasant-tasting fruit. These rootstocks occasionally produce their own branches or suckers, and if they are not removed, they compete with the scion (grafted variety) and make fruit that tastes bad. This also happens, especially with young trees, when the desired variety is killed by cold weather and the rootstock grows in its place.

Inspect your tree to determine if the growth is originating from above or below the bud union. The bud union is usually about six inches above the soil surface. Typically there is a change in bark color or texture between the scion and rootstock that marks the area. Anything growing from below the bud union is likely to produce sour fruit.

Q: My bromeliad houseplant has produced several offshoots around its base. How should I remove them?

A: After flowering, the mother bromeliad plant normally produces several offsets, commonly called pups. Once those growing near the soil have developed their own roots, they can be cut away from the parent plant and potted. Those growing higher up on the plant can simply be cut away and rooted as you would any other cutting. Be sure to use a coarse, well-draining potting mix suitable for bromeliads.

Q: We have a vacation cabin in the mountains. The surrounding soil is very deep in pine needles. Once the snow is gone, are they worth gathering for use as mulch in our garden?

A: In many areas of the country, pine needles are a common mulching material. Mulches have many advantages. They help conserve soil moisture, insulate the soil from temperature extremes, help suppress weeds, and protect the soil from erosion.

Pine needles have additional advantages when used as mulch. They are easy to work with and resist compaction. They are more durable than many other kinds of mulching materials because of their high resin content. You should not have to renew them more than once a year. In addition, pine needles are acidifying, so they are especially valuable for use around plants that prefer acid soils. Finally, they are renewable. A pine tree continues to produce needles throughout its life, whereas bark mulches come from felled trees.

All in all, I would not hesitate to put pine needles to work as garden mulch.

Q: We have several acacia trees that need pruning. When is the best time to do it?

A: Acacia may be pruned at any time of year but the best time to do it is while the tree is in bloom or immediately afterward. As with all tree pruning, first trim any broken branches and correct any branches that are rubbing or crossing. Next, you should thin interior branches to reduce wind damage and dieback from excessive shading. This thinning should be accomplished by removing entire branches to the trunk. Finally, trim to shape or reduce size. By following these basic steps, you should have an attractive and healthy acacia tree.

Citrus ID



Swingle and Reece (1967) noted that:

“This species was introduced into the Mediterranean region from the East and for many centuries was the only orange known to Europeans. During this long period of culture it became very well known and much appreciated as a medicinal agent; the fruits were used for flavoring and for marmalade, and the flowers for perfumery. It was the orange of late medieval Europe. Good high-flavored varieties of the sweet orange, C. sinensis , did not reach Europe from southeastern Asia until the fifteenth century. From that time on there was more or less confusion over the name of the sour orange. The pharmacologists persisted in calling it C. aurantium and the citrologists, then the botanists, called it C. bigaradia. Many botanists considered both the sour and the sweet orange as merely varieties of a single species. As a matter of fact, the sour orange (C. aurantium) and the sweet orange (C. sinensis) are very distinct botanical species, not merely cultivated varieties of one species.”

Hodgson (1967) additionally noted that:

“Like most of the other citrus fruits of commercial importance, the sour, bitter or Seville orange is considered to have originated in the region of northeastern India and adjoining portions of China and Burma. Spreading northward to Japan and westward through India to the Mediterranean basin, it finally reached Europe sometime around the Christian era. The sour orange was among the first citrus to be taken to the New World. In such climatically favorable portions of the New World as Florida and Paraguay it escaped from cultivation and became feral. It is the naranja agria or amarga of Spain, melangolo or arancio amaro of Italy, bigarade or orange amére of France, khuskhash of Israel, khatta of West Pakistan and parts of India, and daidai of Japan.”


Crown compact or dense; not weeping. First year twig surface glabrous or pubescent; second or third year twig surface striate; thorns absent or not persistent or straight; prickles absent or not persistent. Petiole glabrous or pubescent, length short, medium or very long, wings absent, if present, narrow, medium or wide, adjoining the blade or tucking beneath blade. Leaflets one, margin entire, crenate/crenulate, bluntly toothed or serrate/serrulate, shade leaflet blades flat or weakly conduplicate, sun leaflet blades weakly or strongly conduplicate. Leaflets sweetly orange-like (?), spicy or peppery or somewhat to strongly malodorous when crushed. Fruit broader than long or as broad as long or longer than broad, rind variegated, light green with some break to yellow (5), green-yellow (6), yellow (7-10), yellow-orange (11), orange (12) or red-orange (13), rind texture smooth (1-3), slightly rough (4-5), medium rough (6-7) or rough (8), firmness leathery, navel absent or present, flesh orange or yellow, taste acidic-sweet or sour.

Swingle and Reece (1967) provided the following additional notes on the species:

“A medium-sized tree up to 10 m high, with a rounded top; twigs angled when young, with single, slender spines, often short, or stout spines up to 5-8 cm long on rapidly growing shoots; leaves medium-sized, ovate, bluntly pointed at tip, broadly rounded to cuneate at base; petioles 2-3 cm long, rather broadly winged, often 1.2-1.8 cm wide at top, but sometimes narrower, 1 cm or less, narrowing rapidly to the wingless base; flowers large, very fragrant with oil of neroli; 5-12 per cent male (staminate only); fruits subglobose, usually slightly depressed at both base and top, peel thick, with a rather rough surface, becoming brilliant orange with a reddish tint at maturity; locules 10-12, filled with sharply acid pulp and numerous seeds; fruit becoming hollow at center as it matures, and then able to float in water. (See Hodgson’s account of the cultivated varieties of the sour orange in chap. 4 of this work)”

“The chief morphological differences are as follows: In the sour orange the petioles are much more broadly winged than in the sweet, and the leaf blades are narrower and more acutely pointed at the apex, and less rounded and more cuneate at the base. Ruggieri has shown (1935) that the petioles of the sour orange are much the longer, averaging 25.89 mm, whereas those of the sweet orange average only 15.91 mm; in other words, the sour orange petioles average 63 per cent longer than those of the sweet orange. The fruits of the sour orange are of a brighter orange color and have a rougher peel; moreover, in the sour orange the oil glands are situated beneath minute sunken areas in the peel, whereas in the sweet orange the tissue covering the oil glands is often convex.

Uphof reported (1932, pp. 133-35, fig. 4) that he found no male flowers on several cultivated varieties of the sweet orange (C. sinensis), but that he did find from 5 to 12 per cent of male flowers on the sour seedling oranges of Florida (C. aurantium ). The sour orange, according to Uphof, “probably is very close to the sweet orange but from the standpoint of the production of male flowers constitutes a transition, so to speak, toward the lemons, limes and citrons.” Uphof found no male flowers on cultivated varieties of the grapefruit (C. paradisi ). Many trees of the Dancy tangerine (C. reticulata) showed no male flowers (one small tree overloaded with a very heavy bloom had one single male flower among the thousands examined). Tangelos (hybrids of C. reticulata with C. paradisi) also showed no male flowers.

In view of these facts, it is clear that the occurrence in appreciable numbers of male flowers in C. aurantium constitutes an important differential character separating this species from C. sinensis.

The ethereal oil in the leaves, flowers, and fruits of the sour orange is of very different odor than that in the sweet (more agreeable and aromatic in the sour orange) and has a different composition. Also the oil recovered from the petals of the sour orange, neroli oil, finds a different use in perfumery and has a higher value than that of sweet orange flowers. This oil, considered by perfumery experts to be “indispensable to finer perfumery,” is said to owe its high value to small amounts (only 0.4 to 1.0 per cent) of “a nitrogenous compound of exceeding fragrance,” methyl anthranilate, NH2 · C6H4 · COOCH3 (see Gildemeister and Hoffmann, 1922, pp. 93 and 96; and Finnemore, 1926, pp. 436-41). This remarkable substance is not found in the oil extracted from the petals of the sweet orange (Theulier, 1902). The pulp of the sour orange is intensely sour, with a bitterish aftertaste, in contrast to the sweet, agreeable flavor of the sweet orange.”

“The sour orange also shows physiological differences from the sweet orange. It stands winter cold better and has almost complete immunity to the foot rot, or mal di gomma, so destructive to the sweet orange in some localities. However, the sour orange is severely attacked by the scab fungus, Elsinoë fawcetti, which does not attack the sweet orange.

Besides the morphological, chemical, and physiological differences…there are further anatomical difference discovered by Ruggieri (1935) between the sour and the sweet orange in the separative layer of articulation that lies between the petiole and the leaf blade, which may be summed up as follows: (1) The pith in the lower articulation joint where the petiole joins the twig is much more flattened from the top to the bottom in the sweet orange than in the sour. In the sour orange the ratio of the pith to the woody cylinder averages 1:1.4, measured in a horizontal direction, and 1:2.2, in a vertical direction, whereas in the sweet orange the ratio of pith to woody cylinder is 1:1.5 horizontally (about the same as in the sour orange) and 1:4.5 in the vertical (dorsiventral) direction, or only half as thick as the pith of the sour orange petiole. (2) The cells of the interior layers of the cortical parenchyma of the upper articulation joint where the petiole joins the leaf blade are isodiametric and are 12 to 20.5 mu in diameter in the sour orange but are 20 to 27 mu in diameter in the sweet orange, or nearly one-half larger than in the sour orange. (3) The pericycle fibers that form a more or less interrupted sheath around the woody cylinder are strongly thickened in the sour orange but are little thickened, if any, in the sweet orange.

B. Miyazaba, S. Matsubara, and T. Kawaida (1928, p. 189, figs. 4, 5) have also found other anatomical characters that separate the sour orange from the sweet. Comparing the common sour orange (kaisei-to) of Japan with the Washington navel orange (tento) in leaf structure, they found that the sour orange leaf is thin (197 to 274 mu, the average of the ten measurements being 243.38 mu), whereas the sweet orange leaf is about 11.1 per cent thicker (247 to 334 mu, the average of the ten measurements being 270.33 mu ). The two layers of palisade tissue are about the same thickness in the two species, but the spongy tissue shows a wide variation, being only 148 to 189 mu thick in the sour orange leaf (the ten measurements averaging 167.28 mu) but ranging from 165 to 231 mu in the sweet orange leaf (the ten measurements averaging 197.51 mu), or nearly 17 per cent thicker. They also found that the number of stomata is somewhat greater in the sweet orange epidermis than in that of the sour orange, averaging 23.44 in the microscope field of vision for the sweet orange and 20 for the sour orange, or 17 per cent more for the sweet orange.

In view of this array of anatomical, physiological and chemical differences between the sour and the sweet orange it is obvious that they are distinct species even if the gross morphological differences between them are small.”

Hodgson (1967) provided the following additional notes on the species:

“While the sour and sweet oranges have close resemblances there are important differences which clearly justify their separation into different species. The sour orange leaf is somewhat darker in color and more taper-pointed and the petiole is longer and more broadly winged. The fruit is usually flatter and more deeply colored and the rind thicker and more loosely adherent. The rind surface is generally rougher and is minutely pitted with sunken oil glands. The core is normally hollow and the flavor sour with pronounced bitterness in both carpellary membranes and albedo. Most distinctive and easily recognizable differences relate to the odor of the oils in the leaves and rind. In the sour orange the leaf oil is agreeable and distinctive, whereas in the sweet orange it is merely pleasant. Sour orange rind oil is strong and somewhat disagreeable in contrast with the sweet and pleasant odor of sweet orange rind oil. Moreover, the chalazal spot is purple-tinted in the sour orange, reddish-brown in the sweet oranges in general, red in the deeply pigmented blood oranges, and cream-colored in the sugar or acidless oranges (Chapot and Praloran, 1955).

In comparison with the sweet orange, the sour orange tree is more upright and thorny and much more resistant to such unfavorable environmental conditions as frost, excess soil moisture, and neglect. However, the sour orange does not attain as large size as the sweet orange. It is also much more resistant to the widespread gummosis (mal di gomma) disease. In addition, it is susceptible to verrucosis (scab) and markedly intolerant to the tristeza virus when used as a rootstock, while the sweet orange is highly resistant to both diseases.”


Swingle and Reece (1967) additionally noted that: “Furthermore, the peel of the sour orange, which is official in the British Pharmacopœia (the peel of both the sour and the sweet orange is official in the U.S. Pharmacopœia), contains three glucosides, according to Tanret (1886, p. 518): (1) 4 to 30 parts per 1,000 of isohesperidin (= naringin ?), having the same percentage composition and the same rotary polarization as hesperidin but a bitter taste (hesperidin of the sweet orange is tasteless) and a very different solubility; (2) 15 to 25 parts per 1,000 of aurantamarin (to which, so Tanret asserts, most of the bitter taste of the sour orange peel is due), differing slightly in composition and in solubility from both naringin (?) and hesperidin; and (3) from a mere trace to six parts per 1,000 of hesperidin. In the sweet orange only this last glucoside, hesperidin, is found, but it is present in much larger quantities than in the sour orange.”

Hodgson (1967) additionally noted that:

“The fruit is too sour and bitter to be acceptable to most palates, although it can be used to make a distinctive and refreshing drink. Its principal use, however, is in the preparation of a distinctive marmalade, much in demand and appreciated in Europe and especially so in Great Britain, for which sweet orange marmalade is not an acceptable substitute. To meet this demand, sour oranges are grown to a limited extent in most of the Mediterranean countries. The principal producing area, however, centers around Seville in southern Spain, where commercial plantings are currently reported at approximately 4,000 acres. Great Britain comprises the principal sour orange market. Other products obtained or made from the fruits include rind oil and the liqueurs curaçao and Cointreau.

Oil of petit grain is distilled from the leaves and young shoots and oil of neroli from the flowers. For these products, however, which are much used in perfumery, special varieties selected primarily for flower production constitute the principal source of production. A byproduct of this process is orange flower-water, also used in perfumery, for flavoring cakes, and for medicinal purposes.

The importance of the sour orange in the citricultural world, however, arises from its use as a rootstock. Because of its marked resistance to the soil-inhabiting fungi principally involved in the gummosis and foot rot (mal di gomma) diseases, a century or more ago it became the leading rootstock. While its use as a rootstock has declined greatly in recent years because of marked intolerance to the tristeza virus disease, and it now seems destined to be abandoned for that purpose, sour orange remains a major rootstock in the Mediterranean basin and some other areas.

Because of the attractive appearance of both tree and fruit and their hardiness and resistance to unfavorable conditions in general, the sour oranges are also useful as ornamentals.

Three natural groups are distinguishable in the sour oranges, namely the common bitter orange, bittersweet orange, and the variant bitter oranges.”

Finnemore, H. 1926. The essential oils. E. Benn, Ltd., London. 880 pp.

Gildemeister, E. and F. Hoffmann. 1913–22. The volatile oils. Second edition. Authorized translation by Edward Kremers. John Wiley & Sons, New York. 3 vol.

Miyazaba, B., S. Matsubara, and T. Kawaida. 1928. Inner morphological studies on Citrus species and their varieties. Studia Citrologica 2: 185–205.

Ruggieri, G. 1935. La diversa resistanza alla defogliazione prodotta dal vento in alcune specie di “Citrus” in rapporto alla struttura anatomica del picciolo. Bolletino della Reale Stazione di Patologia Vegetale Nova Seria 15: 169–199.

Tanret, C. 1886. Sur quelques principes immédiats de 1’écorce d’orange amére. Comptes rendus de l’Academie des Sciences Paris 102: 518–520.

Theulier, E. 1902. Etude sur 1’essence de fleurs d’orangers douces ou néroli portugal. Bulletin Societe Chimique de France, Ser. 3, 27: 278–280.

Uphof, J.C.T. 1932. Wissenschaftliche Beobachtungen and Versuche an Agrumen. IV. Der polygamische Zustand einiger Citrusarten. Gartenbauwissenschaft 7: 121–141.


Search for this cultivar in NPGS/GRIN1

Search for this cultivar in NCBI2 Entrez, NCBI Nucleotide or NCBI Expressed Sequence Tags

1GRIN: Germplasm Resources Information Network; NPGS: National Plant Germplasm System

2NCBI: National Center for Biotechnology Information

When to pick oranges and tangerines

A friend asked me how to know when to pick the tangerines from his tree. My first thought was, it’s obvious, you pick them when they taste good. But then I remembered that for some people gardening is full of rights and wrongs; he was afraid there was a correct or incorrect time to pick his tangerines.

There’s no such thing.

“Are the fruit mostly orange?” I asked.


“Then taste one.”

“I have.”

“Did it taste tart? Did it taste OK?”

“It tasted good, definitely not tart.”

“Then it’s time.”

Color: the weak indicator

We had been surfing during that terse exchange, but we don’t have to shout in between waves here. So let’s get nuanced, botanical, even maybe philosophical.

Part of the maturing process of oranges and tangerines in Southern California is that they eventually fade their rind color from green to orange. No sweet oranges or tangerines that I know of will be ripe in our climate before they’ve turned orange. So once they’ve changed color, you can consider giving them a pick and taste.

However, it’s true that some varieties turn orange long before they taste sweet. Take the Gold Nugget mandarin, for example. It’s a “late-season” mandarin. Here is a photo I took of my tree on January 15.

Orange fruit: they look ready. But they were still pretty sour on this date. Gold Nuggets from this tree don’t taste sweet until March at the earliest. So the rind color is something of an indicator of maturity, but its not directly linked to how sweet the inside is.

What causes the rind to turn orange, then, if not overall fruit maturity? Let me show you some “mandarinas” that I bought on a recent trip to Costa Rica.

(As an aside, let me acknowledge that I’m using “mandarin” and “tangerine” interchangeably in this article even though a citrus taxonomist would rightly point out that they’re not synonymous.)

If found in a grocery store in the U.S., they’d never sell. But they’re as mature and colored as they’ll ever get there. Nighttime low temperatures in Costa Rica are not low enough to turn them a uniform and beautiful orange, as they get in California. Oranges and tangerines grown in California are far prettier than those grown in tropical climates, and it’s because of our colder nights. (Read more about citrus peel coloration in this University of Florida publication.)

Our oranges and mandarins taste better too, in my opinion; they have more citrus tang whereas I find the tropical fruit insipid.

Taste: the conclusive criterion

Taste is subjective, of course. Yet taste is the only conclusive test of whether or not it’s time for you to pick the oranges and tangerines from your tree. My friend said he’d picked some of his tangerines and they’d tasted fine. I told him it was time to pick them then. The right time to harvest is whenever they taste good — to you.

Or your wife. My wife likes her citrus tart. I pick them for her at least a month before I start picking for myself. Oranges and tangerines get sweeter the longer they hang on the tree.

Growth process of oranges and tangerines

Here is how an orange or tangerine grows: In the late winter or spring, the tree flowers. Small green fruitlets form and enlarge through the summer. In the late fall, they start to change from green to yellow to orange — each variety on a slightly different schedule, and each variety a slightly different hue, ultimately. But it’s the chilly nights of November that coincide with maturing fruit to transform the rind color from green to orange, and it so happens that in the late fall the earliest of tangerine varieties also start tasting sweet. (Think Satsuma and Kishu.) Some others, however, remain tart until the spring (a full year of growing on the tree). Valencia oranges take so long to sweeten that there are two generations of fruit on the tree simultaneously, as you can see in the photo at the top of the page.

As I said, all oranges and tangerines get sweeter the longer they remain on the tree so if you taste one and it’s more acidic than you like, give the others more hang time. Eventually, they will reach their peak of sugar, nadir of acid. Their rinds will become more loosely attached to the flesh inside, making them easier to peel. But also, the pulp inside will proceed to start drying out. At last, the fruit begins to drop to the ground and rot.

What all citrus do not do, by the way, is ripen more after being picked from the tree. That is, the fruit will not get sweeter on your kitchen counter. Citrus are not “climacteric” fruit; they are unlike bananas, for example.

Test case: Secret tangerine

We call this our “secret tangerine” tree.

It’s an old tree that continues to survive and produce fruit in an unirrigated far corner of our property. We don’t know the variety; we didn’t plant it. But over the years, we’ve discovered that it tastes good after all of our other tangerines, about the same time as our Valencia oranges. Still, every year, we go through the “pick and taste” routine until we really start the harvest. Here at the end of spring is that time, my children and I are very happy to report.

Harvest charts

The good news is that oranges and tangerines do not transform in flavor very fast. They don’t have a two-week window of good eating like some peaches, for example. If you harvest citrus and like the taste, you don’t need to pick them all within that week, lest they rot and be wasted. All varieties that I know of “store” on the tree for months.

Which months? If you know the variety name of your fruit, you can get a rough idea of when to pick the fruit by using some of the harvest data within the University of California, Riverside’s Citrus Variety Collection.

Or check out this chart from Four Winds Growers, located in Northern California.

And here is an amazing, fancy chart that I made of the harvest times of the varieties that I grow in my yard (I’m in inland San Diego County):

Maybe you have one of these varieties too. All the while, remember that your tree is not going to mature its fruit at exactly the same time as another in another location — even if it’s the same variety. Your yard’s micro-climate is different.

For reference, in inland locations where it heats up more as well as earlier in the year, harvest dates are earlier compared to locations close to the beach. So my mandarins taste sweeter before yours in Oxnard do. Yet, mine will become over-mature long before those in Oxnard.

In addition, certain oranges and tangerines may never get as sweet as you hope if you live in sight of the ocean. I occasionally pick navel oranges from trees growing at the Salk Institute at the University of California, San Diego, near the Torrey Pines golf course. Those oranges are always so bland that they are barely worth eating.

The weather every year is also different. No two years will have the exact same harvest dates. My Valencia oranges taste excellent here on June 1, 2018 whereas they usually reach their peak flavor at the end of June. This past winter was extraordinarily warm.

What I like to do for my orange and tangerine (and all other fruit) trees is associate the harvest season with a birthday or holiday. Come to think of it though, I only use a version of this strategy for my Valencias. In my mind, I can never forget when to pick them because I grew up swimming in my grandparents pool during the summer and taking breaks beside one of their Valencia trees getting sweet, sticky juice all over my face, chest, and hands.

Here is a short video describing when to pick oranges and tangerines:

You might also like to read my post:

When and how to prune citrus trees

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