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Cold Hardy Citrus / Orange tree in zone 8
« on: September 17, 2018, 01:49:26 PM »
This is based on a previous thread, and I thought to make a new thread on the topic, sharing some of my knowledge and thoughts.

Some of you living in zone 8 may be wondering if it's possible to grow an orange tree outside, or whether there's any kind of orange tree hardy down to zone 8a.

Well first, let me explain something. The most common citrus that people normally want to grow, oranges, regular lemons and limes, these are some of the least cold hardy citrus varieties. It's no wonder then that there's a common perception that citrus doesn't grow in zone 8, because normally when people have tried growing citrus, these are the types they have tried.

Now, before I explain further, I would like to share an optimistic story with you.


North Waco family's orange tree a miracle on 15th Street
by J.B. Smith, January 2013

A tree that Juana Delgado grew from the seed of a grocery store orange has become a miracle on 15th Street.

This month, Delgadoís family has harvested an estimated 600 oranges from the tree she planted 15 years ago when she moved into the Habitat for Humanity home near North 15th Street and Colcord Avenue.

In recent weeks, the family made big jugs of orange juice, shared fruit with passing vagrants and sent their children door-to-door to give away large bags of juicy oranges.

The tree has defied the conventional wisdom that oranges can't survive the Central Texas winter, when temperatures usually dip into the low 20s.

But the tree has soldiered on, even through a January 2010 cold snap when temperatures plummeted to 8 degrees.
"Many people said itís not possible," Delgado said in Spanish. "I say, 'Come look. It's possible.'"
Mark Barnett, a McLennan County master gardener and a landscaper by trade, said he has seen many people try to grow citrus trees they bought from big box stores, but the trees usually freeze and die.

"It's very unusual for it to have survived that long without protection," he said. "We've had some extremely cold winters that should have killed it."

Delgado started the orange tree in a pot using a seed from an orange she bought at an H-E-B supermarket. Most table oranges are improved hybrid varieties and tend not to reproduce faithfully by seed, Barnett said.

But Delgado's oranges turned out sweet and flavorful. Delgado has been harvesting a few oranges a year during the last decade but got her first big harvest two winters ago: A basket and a box full. In the 2011 drought, she kept the tree alive by watering it but ended up with only three oranges that season.
This year, she hit the jackpot. Her children and grandchildren climbed ladders to pick the fruit and filled six boxes with about 100 oranges each.


Waco, Texas, is in zone 8a, and is just a little south of Dallas. Although in recent years the 8b zone has been moving north, first the southern half of Waco was reclassified into zone 8b, and now on the latest maps zone 8b has engulfed the entire city.

I've also speculated in another thread that citrus grown from seed may have more cold hardiness in zone 8 than the usual citrus on rootstock. (This doesn't necessarily apply in zone 7 though)

So now you know there's some hope an orange tree may be able to survive in zone 8. But don't get your hopes up because this is zone 8 in the American South and Texas. All the heat during the growing season (mostly because the growing season is longer) helps the citrus put on a lot of growth and better recover from the Winter. And there may be the odd year once in a while, with an exceptionally cold Winter, where your tree is going to killed to the ground. That's the type of climate that exists in the Southeast and Gulf Coast.

But now going back to the original topic. Are there any type of Oranges that are more hardy? Or are there any orange-like citrus that are more hardy?

The only actual orange that I'm aware of that has a good chance of surviving in zone 8a is Chinotto orange. It's actually more of a sour orange, the type good for making marmalade. You can eat it, but it's not as good eating quality as a regular orange.

Then there is Bloomsweet grapefruit. It's not really a "real" grapefruit. In form and flavor it's more like something halfway between an orange and grapefruit. The eating quality isn't bad but the eating quality isn't really quite as good as the oranges or grapefruits you can find in a supermarket, and it is full of seeds. (It is believed Bloomsweet may have come from a variety in Japan named "kinkoji", and a genetic analysis has shown it to be half-sibling to the popular variety Satsuma)

Tangelos have more cold hardiness than oranges. I'm not saying a tangelo is going to grow well in zone 8a, but it's probably going to have a much better chance than orange. Minneola tangelo has great flavor, but Orlando tangelo is known to have slightly better cold hardiness than Minneola.
In general, mandarins (sometimes called "mandarin orange") are more cold hardy than oranges. Not incredibly cold hardy, but mandarins can be commercially grown on the border between zone 9a/8b.

If you're interested in juicing, FF-6-15-150 is a newer one that came out of a USDA breeding program in Florida, and is rated to be as hardy as the cold hardiest commercial mandarin varieties. It was in large part bred from Orlando tangelo, is said to have great flavor, though seedy and on the small side for an orange. But it's not commonly available to the public and may be difficult to get your hands on.

Calamondin is believed to have originated from hybridization between kumquat and orange. It has more cold hardiness than orange, can grow in zone 8b, and has a chance of growing in zone 8a (maybe not as well). Mandarinquat is similar, it's a hybrid between kumquat and mandarin, and has slightly more cold hardiness than calamondin. The inside flesh of a mandarinquat is better than a kumquat, but although it can be eaten like a kumquat, the skin is a little bit tougher and not as good. And of course this section wouldn't be complete without making quick mention to Nippon Orangequat (a hybrid between kumquat and Satsuma mandarin). It has the best chance of doing well in zone 8.

Changsha mandarin and Citrange (a cross between Orange and bitter Trifoliate Orange) are two more pretty cold hardy ones that are distantly orange-like, sort of, if you're willing to drastically lower your expectations of fruit quality and flavor.

There are many other citrus varieties that have more cold hardiness but none of them are really "orange-like", so we won't really go into that discussion here.

Cold Hardy Citrus / Grapefruit that grows outside in England
« on: September 17, 2018, 01:27:39 PM »
There is a grapefruit tree growing outdoors, and which produces fruit, in the Chelsea Physic Garden, located in London.


A little bit of information about this grapefruit, it started off as a seedling sown in 1948 and kept in a pot until 1990, when the original owner died. It has fruited regularly every year since 1998.

It has been nick-named 'Aunt Queenie'.
The tree is located in a sheltered corner up against a brick wall under the protection of a large olive tree, and produces regular crops of large yellow fruits that hang for months on its branches.

With the thick pith and small fruit size, it doesn't look like those fruits are ripening very well in the cool climate.

A couple of possible factors that may be contributing to it being able to grow so far North: it is located in the center of a large city which probably has an effect on the localized climate, the garden is located next to the Thames river which may be having a moderating effect on the nearby temperature, the tree is growing in the corner of a sheltered walled garden. The fact that it was grown from seed and is not grafted onto a different rootstock might also be making the plant more vigorous and resilient to the cold. Since it is a white grapefruit, the variety it was sown from was most likely Duncan or Marsh, which are a bit more hardy than other common grapefruit varieties.

Cold Hardy Citrus / Re: citrus varieties in order of cold-hardiness
« on: September 17, 2018, 12:16:46 PM »
level of cold hardiness order for kumquat and common related hybrids

kumquat > mandarinquat > calamondin

Some more information on relative cold hardiness of different citrus, now going into some of the varieties that are not very hardy

Citron is basically the ancestral species from which lemons descend from. (ordinary lemons)
Citron has even less cold hardiness than common lemons. Common lemon varieties in turn do not have as much hardiness as Meyer lemon, which is believed to have originally resulted from hybridization between mandarin and citron in China, and has a separate (but somewhat similar) ancestry from other lemons whose history dates to Southern Europe.

Limes have less hardiness than lemons, making them the least hardy common citrus group. Limes are mainly descended from an the citrus species C. micrantha, which has even less cold hardiness than limes.
One exception, Kaffir lime is in a separate group, believed to be descended from an origin citrus species known as Khasi papeda (C. latipes), and has some small degree of cold hardiness, more than lemons.

In form, the fruits of citron appear quite similar to Ichang papeda, in fact the two species may be less distantly related to each other than to other citrus species, but whereas Ichang papeda is the second most cold hardy citrus species, citron is the second least cold hardy species. (so quite a difference in terms of level of cold hardiness!)

I've been wanting to attempt a hybrid between citron and Ichang papeda as the first step in trying to breed a lemon (a true lemon) with more cold hardiness.
Maybe the 2nd step would be to cross the result with Duncan grapefruit or pomelo, or something like that.

While Meyer lemon is the cold hardiest of the true lemon varieties, and I am a really big fan of lemons, I'm just not really a big fan of Meyer lemons.
(But that's personal preference, some people say Meyer is their favorite lemon variety)

Cold Hardy Citrus / Re: citrus varieties in order of cold-hardiness
« on: September 17, 2018, 10:54:33 AM »
-----"There are many grapefruit varieties that are cold hardier than many different tangerine varieties."-----

SoCal2warm, as you must actually believe the above quote, then please name them so others can evaluate your statement.

Duncan and Marsh (both white grapefruits) are commonly regarded as the most cold hardy grapefruit varieties.

There are a few seedling grapefruits that purportedly have survived in South Carolina (though anecdotal evidence suggests they sometimes die back during very cold years but in some cases can regrow).
There is even one instance of a white grapefruit originally grown from seed which managed to survive in very sheltered spot in London (yet outside uncovered).
(see thread here: )

I just meant that, in general, mandarins are more cold hardy than grapefruits, but some grapefruits, like Duncan, have more cold hardiness than some mandarin varieties like Clementine, so there can be considerable overlap depending on the exact variety. (Of course Duncan is not as hardy as Satsuma mandarin)

The hardiest variety of the common mandarin varieties is Satsuma. ( "common" meaning commercially edible quality)
Although it would be a bit more accurate to say that Satsuma is actually really more of a subgroup of mandarins, with several different varieties within it.

FF-6-15-150 is a new mandarin variety that came out of a USDA breeding program in Florida which is rated to have as much cold hardiness as Satsuma mandarin (though not related to Satsuma). It has Orlando tangelo in its parentage.
Lee mandarin x Orlando Tangelo
Lee mandarin itself was bred from Clementine x Orlando Tangelo
Orlando tangelo is a slightly cold hardier sibling of Minneola Tangelo, being bred from a cross between Dancy mandarin x Duncan grapefruit
FF-6-15-150 resembles a small orange or Page mandarin, said to have good flavor good for juicing, though does contain a fair number of seeds.

Cold Hardy Citrus / Re: citrus varieties in order of cold-hardiness
« on: September 17, 2018, 10:35:50 AM »
Citrumelo (has survived in zone 7b in the South, and a few cases growing in zone 8 England)
Ichang papeda (cold hardy down to the border of zone 8a/7b in the South, zone 8a in a sheltered location in the PNW)
Yuzu 10 F
Changsha 10-12 F
Arctic Frost 10-13 F or 10-15 F (this is a Changsha x Satsuma cross, a few people have suggested this may not really be much hardier than regular Satsuma)
Ten Degree tangerine 11.5 F or 10-14 F (this is a Clementine x Yuzu cross)
Keraji 12-14 F

Indio mandarinquat 14-23 F probably
Bloomsweet 18 F or 15-23 F probably (might be just slightly hardier than Satsuma)
Nippon Orangequat 14 F or 10-16 F

Ichang lemon 15-20 F (or might have close to the same level of cold hardiness as Yuzu, genetic studies have suggested this is a Pomelo x Ichang papeda cross)

Cold Hardy Citrus / Re: Kumquat x Poncirus
« on: September 17, 2018, 09:35:31 AM »
You might get something even cold hardier on the second cross, that is, if you try to grow a seedling of the poncirus x kumquat hybrid. That would be due to possibility of recessive genes or weeding out a dominant gene that may be detrimental.
Unfortunately I would expect a poncirus x kumquat hybrid to be highly nucellar. You'd have to go through a lot of seeds to find a nucellar one, if there were any.

I've heard that kumquat x Satsuma can be pretty cold hardy, down 14 degrees F.

Kumquat is usually always zygotic, so you could always perform a second generation cross by using it as the fruit parent.
That is kumquat x (kumquat x poncirus)

Cold Hardy Citrus / Re: how can I keep citrus trees in optimum temp
« on: September 14, 2018, 04:33:51 AM »
For a 2 by 3 foot space, two "100 watt equivalent" (5000K) LED bulbs, constantly left on, are sufficient for lighting.

It is also possible to buy a temperature controlled thermostat outlet, and plug in a tiny 250 Watt space heater to that to supply warmth. But for citrus growing inside a heated house (and in the geographic location you are) that will probably not be really necessary. Even without an added heater the temperature is still likely to stay about 63 F (17.5 C) in there, with the lights being on, even though it may be 0 C outside.

Plan to water about once a week, maybe twice a week if the containers are not really big enough.

Cold Hardy Citrus / Re: Citrus in the Pacific Northwest
« on: September 11, 2018, 12:07:07 PM »

The Yuzu has put on more growth.

I think the rainy season has started (it began raining heavily yesterday).

Cold Hardy Citrus / Re: Arctic Frost beginning to come back
« on: September 11, 2018, 12:02:44 PM »

The rainy season has started and temperatures are beginning to cool down. I suspect the growing season has ended, as far as the amount of warmth citrus needs to add growth.

Cold Hardy Citrus / Re: citrus grown from seed shows more cold hardiness
« on: September 11, 2018, 11:58:41 AM »
In plants both somatoclonal variation ( due to mutations arising and darwinistically selected in individual cells of multicellular organism) as well as environmentally induced epigenetic modifications can be transmitted to  to clones or  maintained in zygotic seedlings.
That's very fascinating but I haven't seen much evidence of this (epigenetic modifications passed to clones or seedlings.

Cold Hardy Citrus / Re: citrus grown from seed shows more cold hardiness
« on: September 10, 2018, 02:50:22 PM »
Lemon tree grown from seed survives left outside in a large container over the Winter in Tennessee

He grew the lemon for 13 years before leaving it out outside on his porch. He says he is in zone 6b.
 There's a picture of the tree, it looks healthy and about 3 or 4 feet tall.

He also says in a later comment that his porch is on the North side of his house, and gets no sun in the Winter.

"Every winter the last three years we've seen a -10 temperature appear on the thermometer multiple times. The measurements were actually taken near the house which may be a little warmer than farther out in the yard. We definitely get cold here!"
(that would be degrees Fahrenheit)

Another anonymous commenter also left this comment: "I have a Lemon tree that has lived outside for 3 years with Lemons on it now. I live in Tn." (Tennessee)

Cold Hardy Citrus / Re: citrus grown from seed shows more cold hardiness
« on: September 09, 2018, 03:38:22 AM »
Lamarkism, to a limited degree, and on the smaller scale, is a definite valid theoretical foundation for inheritance.
To an extremely limited extent, and it's not entirely clear whether that is the case with citrus, so that is really beside the point.

(Of course science has validated a little bit of truth to Lamarkism, like activation or deactivation of certain genes, and methylation of DNA bases, but I did not want to mention that and overcomplicate things, I think it's pretty doubtful citrus is going to be able to pass down its cold-hardiness gene expression adaptations to its nucellar seed)

Than I do not understand what is your "hypothesis" is about and why you suggested "vigorous" Yuzu for its testing.
Because Yuzu is believed to have originated from interhybridization between sour mandarin and C. ichangensis.

Maybe that wasn't the best example to use.

Calamondin and kumquat. Calamondin, let us assume, contains 50% orange and 50% kumquat genes. If it is hybridized again, it will contain 75 percent kumquat.
 Then I am thinking the genes will be more homogenous, more like the kumquat ancestor, and it may be at least a little bit zygotic.

Or one might have to hybridize it with kumquat again, over another generation, before the seeds of the progeny become zygotic.

From my experience, based on thousands seedlings of 5* citrumelo, its crosses to FD and several grapefruit varieties are almost all very slowly growing plants, while hybrids to Yuzu and oranges have extraordinary rapid growth.
Not really the best example, since citrumelo is already a hybrid. And Yuzu already has very vigorous growth.

Citrus General Discussion / Re: Natural pest control
« on: September 07, 2018, 02:01:41 PM »
I've read some advanced organic gardeners grow N. rustica (a wild form of tobacco) and make a tea out of it which has a very high nicotine concentration, and then spray it as a natural pesticide. Care has to be used, however, since the nicotine can easily absorb through skin, so protective gloves should be worn (and like any pesticide it should be regarded as a poison, ingestion could cause poisoning, concentration of nicotine is a lot higher than ordinary tobacco).

Pyrethrin is derived from chrysanthemums. I've you've ever noticed, insects don't normally attack chrystanthemums.

Usually it is quite an opposite. Due to the hybrid vigor the heterogeneous offspring grows better than genetically homogeneous parents.
Outbreeding depression is more common than hybrid vigor.

I think in general hybrid vigor might be more likely to occur if the two species are very closely related to each other, and each has different types of genes for vigor, whereas outbreeding depression is more likely to occur with more disparate species, that have long ago evolutionarily diverged.

I think it can be assumed that the formation of nucellar seed is either due to hybrid vigor or a form of outbreeding depression, but I am not truly sure which.

Outbreeding depression refers to cases where offspring from crosses between two different populations have a lower level of fitness than offspring from crosses between individuals from the same population.
One of the ways that outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different breeding populations. Within local, isolated breeding populations, alleles are selected for their positive, overall effects in complementary combination with other specific alleles. Due to nonadditive gene action, the same genes may have rather different effects in different genetic backgrounds--hence, the potential evolution of locally coadapted gene complexes. 

Cold Hardy Citrus / Re: citrus grown from seed shows more cold hardiness
« on: September 07, 2018, 01:32:59 PM »
A seedling exposed to cold weather over the years will express genes of cold resistance that will pass to the next generation. Of course this happens over the years.  Perhaps hundreds of years.
That's not really true (or possibly I am just misunderstanding your statement, if it was a poor translation). The theory of inheritance of acquired characteristics (Lamarckism) has been largely disproven since the theory of Evolution and by modern genetic understanding.

Sometimes a seedling will exhibit more cold hardiness than its parents. That's what can sometimes happen when the genes get mixed around.
This would be a zygotic seedling, of course, since nucellar seeds have the same exact genetic composition as the fruit parent, except in rare cases of seed/pollen mutations.

One well-known example that comes to mind is Juanita tangerine, grown from seed which came from an ordinary supermarket-bought mandarin.

Over a long timespan, if a species is continually propagated from seed over several successive generations, there can be some level of adaptation if the progeny that are better adapted have a higher rate of survival or reproductive propagation.

So genetics is another factor that can sometimes cause seed-grown offspring to be a little bit cold-hardier than their parents.

I have theory. I don't have any evidence for it, but let me share the reasoning for it.

Among different citrus varieties there are some which produce a higher percentage of nucellar seeds than others. Some citrus species produce entirely zygotic seed, while other varieties produce almost entirely nucellar seed, and there are several varieties with percentages in between. If the seed is nucellar, it will be a genetic clone of its parent. Not really a good thing if you're trying to hybridize new citrus varieties, but a good thing for those growing rootstock from seed, where uniformity is important.

The reason, it is believed, some citrus varieties form nucellar seed is that the sexual gamete cells inside the seed are not vigorous enough and can't compete with the nucellar cells.

The original origin citrus species are, almost entirely without exception, all zygotic. But when different citrus species are hybridized the percentages of nucellar seed shoot up. This could be because the hybridization between different species (which are not entirely compatible) results in a weaker gamete (megagametophyte), and so the nucellar lining takes over.

My theory is that if a hybrid citrus flower is pollinated with pollen from one of the original two species from which the hybrid originated from, the percentage of nucellar seed is likely to be lower. This would be because, the genetic composition of the megagametophyte would be less heterogenous, and thus presumably have more vigor.

So, for example, if Yuzu were pollinated by C. ichangensis, there might be some zygotic seeds form in the Yuzu fruit.

If this theory is true, this may confer some advantage to hybridizing new citrus varieties, since normally trying to hybridize a variety that is highly nucellar and using it as the female parent presents some pragmatic challenges.

Cold Hardy Citrus / Re: Yuzu... my new obsession!
« on: September 04, 2018, 09:59:07 PM »
A video some of you may be interested in

The mangosteen, after surviving the heat wave

It looks like at least some of the leaves are still lush green, even if badly deformed. I'm not sure whether this is new growth that came out or whether some of the smaller old leaves managed to hang on. It appears to be slowly recovering, although it took a big hit.

Cold Hardy Citrus / Re: Yuzu... my new obsession!
« on: September 04, 2018, 08:06:13 PM »
If anyone wonders what the Yuzu aroma is like, it's like a mix of mandarin orange, satsuma mandarin, sour marmalade orange (C. aurantium), and lemon all combined together. There's a lesser note (maybe 25%) of grapefruit in there, and a very slight but discernable note of guava. There's also something very pungently deep and "spicy" about the fragrance of Yuzu, which is probably one of the first things you'll notice when you smell it. It's a very unique citrus smell.

Tropical Fruit Discussion / Re: I need more guavas in my life.
« on: September 04, 2018, 07:44:06 PM »
I like the smell of guava, it's very tropical and intoxicating, but even though I've tried to like it, I just don't really like eating the fruit. It's either too hard and astringent if not ripe enough, or when it is fully ripe it starts taking on a more putrid smell that is just somewhat offputting to me.

But if something like a Reisling varietal wine is said to take on the flavor of guava, that's a very positive thing. The fragrance is almost floral and edible at the same time.

Temperate Fruit Discussion / Re: hybrids between quince, pear, and apple
« on: September 04, 2018, 04:12:28 PM »
Two fruits on the Passe Crassane

Yes, this is in zone 10, and we had an unusually mild Winter this year on the West Coast, and this is only the third year. So I'm thinking chill hours are not going to be too much of an issue with this variety.

Cold Hardy Citrus / Re: Ichanglemons
« on: September 04, 2018, 03:42:25 AM »
Weird. The arboretum's page uses the phrase "Ichang lemon": (first result)
That picture definitely shows C. ichangensis, rather than the other "Ichang lemon". You can tell by the leaf petioles.

The name "Ichang lemon" is a little bit ambiguous and is sometimes used to refer to C. ichangensis. But of course there's the other Ichang lemon (Shangyuan) which is believed to be a hybrid between C. ichangensis and C. maxima.

In fact, there's no ideal name that exists for this "Ichang lemon" that is entirely exclusive to that variety, for Shangyuan (alternative spelling xiang yuan) also is the name for Chinese citron, an entirely different citrus.

Cold Hardy Citrus / Re: Swamp Lemon Adventure!
« on: September 01, 2018, 03:57:03 PM »
Yes, from that picture comparing leaves it obviously looks like it's much closer to regular trifoliate than to citrange.

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