Main types of Citrumelo

[dd333]

Are there two main types of citrumelo -- lemon and grapefruit?
Or is it just the one which is a lemon and grapefruit hybrid?
The "citrumelo" I grow here, which I was told is the citrumelo lemon, shows no winter damage at all (zone 7b) while what I know as the straight stemmed trifoliate gets killed back to ground in its first winter.
Also, the citrumelo I grow here are all from rooted cuttings from a fruiting parent tree, yet have still not blossomed after 6 years and close to 10 ft tall.
Thanks

[Wahl]

citrumelo are grapefruit X trifoliate. How cold did you get in your zone 7 this year? I have a swingle citrumelo that has made it through for me with some protection and if it gets to cold it does not flower for me, so i have not had and flowers in the last 2 years since it got down to 0F. 3 years ago I got 6 bushels off of it.

[dd333]

Going by an official weather station close to me, it got down to 22 & 23 several times for several hours. 
But the 2 coldest spells where 16 dF for 3 hours on 240117, and 13 dF for 5h on 240121.
Again, what I was told is a citrumelo lemon, shows no damage at all -- other than never getting any blossoms.
This is with no protection at all.

Seems strange that something that is a trifoliate hybrid is hardier than the trifoliate.
Is this what others are seeing?  Or is there some misinformation on what I have?
Thanks for the reply.

[bussone]

Going by an official weather station close to me, it got down to 22 & 23 several times for several hours. 
But the 2 coldest spells where 16 dF for 3 hours on 240117, and 13 dF for 5h on 240121.
Again, what I was told is a citrumelo lemon, shows no damage at all -- other than never getting any blossoms.
This is with no protection at all.

Seems strange that something that is a trifoliate hybrid is hardier than the trifoliate.
Is this what others are seeing?  Or is there some misinformation on what I have?
Thanks for the reply.

13 F is not especially cold for poncirus. I have a young seedling Poncirus that sailed through 14F.

Poncirus is zone 6, so you're looking at -5F or -10F before you are really pushing your luck with poncirus. There's a couple of trees that survive in 5B.

[Wahl]

trifoliate Should not die at 13f It should be able to go down to -10 to -20 or below. If you only got down to 13F this year the citrumelo should have flowered. Did it lose it leafs or keep them?

[SoCal2warm]

In the U.S., the two main citrumelo varieties are Swingle and Dunstan citrumelo. There are some others but they are more obscure.
From what I've read, Dunstan has less of a bad poncirus flavor than Swingle, and is almost a little "lemon-like" in sourness. But Swingle might be a little more vigorous growing and resilient (although Dunstan seems to be decently vigorous growing and resilient growing from my observations).
Both Dunstan and Swingle are siblings originating from the same poncirus x white Duncan grapefruit cross. (For those who do not know, Duncan was considered the original gold standard of grapefruit flavor, although it had a lot of characteristic grapefruit-like bitterness and was seedy. I have tasted it and agree, in my personal opinion, it has excellent flavor and nice tartness, more concentrated and aromatic than other grapefruit varieties, though might not be for those who prefer sweet and mild grapefruits)
I think Swingle became the preferred rootstock variety because it grows more true to seed, 85 to 95% nucellar, versus Dunstan at maybe only 65 to 70%.

[dd333]

Thanks for the replies and great info.
What I'm calling citrumelo and straight stemmed trifoliate in this thread are all from rooted cuttings.
Also, my soil is a terrible yellow or green clay -- which effects vigor, and thus effects cold hardiness.

This citrumelo may have lost its leaves in its first winter, but no kind of leaf loss or die back since established.  The citrumelo parent tree is 20 miles from me and has had regular crops of fruit.  The fruit from the parent tree is very seedy, and a little smaller than a baseball.
Was told by the parent owner it was a citrumelo lemon.  Sounds like this might be the Dunstan sibling.
Guessing it could be my soil that has delayed blossom / fruit production?
Might a foliar spray help start off fruit production?  What kind?

This straight stemmed trifoliate was not killed by its first winter, just hit back to ground level.  Cuttings came from a 10 ft tall tree about 30 miles from me, and that friend reported lots of winter damage to this parent trifoliate that winter.  That winter got off to a strange start with that fall having rapid early temp drops and little / no time for acclimatization.  Temps got down to 9dF for 3 hrs that winter, but I believe it was the very early hard frost that did the damage. 

But again, this Citrumelo sailed right through that same winter with no damage.

If some pics would help confirm anything, of which parts?
Thanks

[a_Vivaldi]

I've can't comment on Swingle. Dunstan to me tastes pretty good and has decent fruit quality overall in my climate. It's quite vigorous here.

Mine is a second year plant from Woodlanders, so it should be three years old. The fruit ice had was from an established tree in Raleigh NC. Seedy in the middle, sweet and tart, very juicy and very aromatic.

The current flush is between 8 and 18 inches of new growth. So much faster than a Satsuma, haha

[a_Vivaldi]

Dunstan fruit

[Mulberry0126]

https://youtu.be/sWMmj09REC4?si=HmBvddd3QHb1N1mU

My wife and I had the opportunity to review the taste of Dunstan, Sacaton, and Swingle, and look to try 5star in the next year or two.
Dunstan, from my memory, can taste very pomelo/sweet grapefruit-like with lemon flavors too and minor grapefruit bitterness. When fully ripe/overripe I taste more trifoliate compared to slightly underripe.
Sacaton is lighter in flavor and very juicy, even more so than Dunstan. It has a flavor reminiscent of grapefruit mixed with sour orange. It has a little more but still minor trifoliate/grapefruit bitterness.
Swingle is interesting because it has grapefruit, sour orange, and lemon flavors as well as a subtle but noticeable mandarin aftertaste in some fruit. It has the most trifoliate flavor but isn't exceptionally bitter, mostly just sour.
I've juiced them and they all make very good "lemonade" that I actually crave when they are out of season. I really enjoyed Dunstan-ade since it was like grapefruit juice and lemonade mixed together. Sacaton and Swingle-ades taste closer to a true lemonade with other citrus mixed in.
I actually prefer Dunstan and Sacaton citrumelo to true grapefruit from the supermarket which are often just watery and bitter - these at least have some flavor complexity.
In terms of seeds - Dunstan seedlings have been highly uniform for us, I haven't noticed more than 5-10% being zygotic. Wholesale Sacaton seeds have also been predominantly nucellar, with few noticeable zygotic seedlings.
Sacaton seedlings from Stan McKenzie's tree however have been extremely variable, with only 1 out of 15 or so resembling the mother tree. This leads me to suspect that they are different strains of Sacaton. Some of our Sacaton seedlings were pollinated by ten degree tangerine and vice versa with some of our ten degree tangerine seedlings.
Swingle is also highly nucellar, definitely the most out of the 3. Though I did manage to find a unifoliate seedling which I have since grafted onto a larger rootstock to expedite it's growth. I'm hoping that 5 years from now I can share our new citrumelo varieties with all of you! Fingers crossed.

Also - we have Dunstan high grafted onto trifoliate orange in New York zone 7a/7b. It's only experienced one Winter so far and sailed through a low of 16°F with no damage or leaf drop.

[bussone]

I've can't comment on Swingle. Dunstan to me tastes pretty good and has decent fruit quality overall in my climate. It's quite vigorous here.

Mine is a second year plant from Woodlanders, so it should be three years old. The fruit ice had was from an established tree in Raleigh NC. Seedy in the middle, sweet and tart, very juicy and very aromatic.

The current flush is between 8 and 18 inches of new growth. So much faster than a Satsuma, haha

Those are some murderous thorns.

[a_Vivaldi]

Oh yes. They make grafting onto that plant quite an interesting experience.

[Till]

 I have tasted Batumi Citrumelo, Dunstan, Swingle 5 Star and a mislabeled Citrumelo with a high rate of zygotic seedlings.
--> Batumi is hardly bitter and has no Poncirus off-flavours. It is sour but very tasty.
--> My Dunstan is as discribed here. Like a good grapefruit only sour. It contains a sticky substance. But the substance is tasteless.
--> Swingle 5 Star is quite bitter, too bitter for me. It has also strong Poncirus off-flavours. For me not edible. But I am willing to believe that it is as good as Ilya describes it in warmer climate.
--> The mislabeled Citrumelo may be Yuma Citrange = Sacaton. This would at least explain the misspelled and strange name the nursery gave to it ("Yuma Gwangne..." from handwritten "Yuma Citrange"?). It is very aromatic and juicy but also bitter with Poncirus off-flavours. Sourness is moderate. I would say: High potential for breeding but almost inedible as it is.

Swingle 5 Star is not hardy in my climate. It is killed to the ground even in mild winters with lows of only -10°C / 14°F. Ilya states a much better frost resistance. But the growing period at my home seems to be too short for better performance. I have not tested the other citrumelos. Seedlings of the mislabeled Citrumelo were all killed to the ground at around -8°C / 17,6°F, except two zygotic ones that only lost their leaves.

Regarding hardiness of Poncirus and Citrumelos, I remember a scientific article that stated a hardiness for Poncirus between -14°C (6,8°F) and -20°C (-4°F) depending on the cultivar. Other sources attributed a hardiness of about -25°C (-13°F) to Poncirus. So the genus Poncirus consists of  different gene lines with different hardiness. I can confirm from own experience that some Poncirus seedlings are hardier than others.

The main challage for Poncirus in my climate (cool atlantic climate) is late frost in spring. It cannot handle late frost in spring (for instance -8°C / 17,6°F at the end of April) very well as a plant adapted to continental climate. In one year, Poncirus was severely frostbidden while Yuzu had no damage at all. (In the next year Yuzu was dead and Poncirus alive.) With this in mind, I can image that a citrumelo is at times hardier than pure Poncirus. a) Hardier when compared to a Poncirus with low hardiness. b) Hardier under late frost when slower to grow in spring. c) Perhaps also hardier when it grows faster than Poncirus so that it hardens off more quickly in autumn.

But usually Poncirus should be much more frost resistant than any of the known citrumelos.

[a_Vivaldi]

I've can't comment on Swingle. Dunstan to me tastes pretty good and has decent fruit quality overall in my climate. It's quite vigorous here.

Mine is a second year plant from Woodlanders, so it should be three years old. The fruit ice had was from an established tree in Raleigh NC. Seedy in the middle, sweet and tart, very juicy and very aromatic.

The current flush is between 8 and 18 inches of new growth. So much faster than a Satsuma, haha

One of the leaders on this Dunstan broke off in some wind, but regardless it seems to be doing well. Might actually pass 5 ft this year. Since this one is just a seedling and is only a few years old, I also grafted some mature Dunstan to it earlier this year. That graft has flushed out and is looking pretty good, hopefully I'll get some blooms next year to take pollen from.

[kumin]

 5* Citrumelo fruits on tree high grafted on Poncirus. This follows 2 Winters with lows of 2° and 6°F in Southeastern Pennsylvania. This tree has never been protected from cold temperatures.

[Wahl]

Looking good there. How was the bloom on it this year?

[kumin]

Modest bloom as it was the first year the outdoor grafts flowered. The sheltered trees flowered and fruited profusely.