Ok @Paul well thanks for your update.
Well, it is good that you have had mild winters the first years. A bigger tree can take more cold. I know my Navel oranges the 1/2" limbs could take like 20F when the upper thinner younger limbs were killed.
I guess everything tends to gain more hardiness when thicker limbs. I cant wait to test what 1/2"and 1" thick Prague limbs can take. I plan to graft more trees and eventually after they get some sizeable limbs, test them in various situations(protected, semi-protected, and unprotected to 0F and -5F etc!) here in kansas 6b. What if an established tree can really take 0F! 
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I wouldnât be surprised if it survived 0F, itâs quite likely actually.
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then itâs not so stupid that I try to create other chimera between Poncirus and Citrus 
so I advise paying attention if a sucker appears from the graft point instead of cutting it off straight away.
Iâm speculating now, maybe it has an influence on the cold hardness, that the trifolia forces the satsuma part to become dormant too, stop growthâŚ
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Dr. Hansen created several graft-hybrid chimera apples between good ones and extremely cold-hardy, otherwise useless ones. Over 100 years ago so itâs a proven technique.
+Laburnocytisis
+Crateagomespilus
Burbank had a spontaneous one that I canât remember.
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Please do! I should try that too! And i plan to plant every Prague seed i get, just in case one in 1000 ends up being a splice/winner!! I say anything is possible!
Wow, so its old proven technology! Lets try it! Im going to watch⌠and you know, im thinking i may have already experienced this in the past on grafts but i tore them off before testingâŚ
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Incredible nursery⌠
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haha i bought mine there 
I HIGHLY suspect the cultivar being referred to as âPragueâ is the same as the chimera I linked to previously that is in the USDA collection.
+Citroponcirus doesnât seem to be a recognized valid name since Poncirus is actually just an outdated synonym for Citrus (trifoliates are Citrus trifoliata - no longer Poncirus). The name used by the USDA is probably incorrect too since Citrus Ăinsitorum refers to a hybrid and this specimen appears to be a chimera rather than an actual hybrid.
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I know the owner, we exchanged in the past. Very nice person. By the way my Prague also comes from her although my local friend had fruit on his citsuma way back in 2014 which I did not know at that time. Bringing scionwood from France when you have it right around the corner 
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I was just able to order some budwood of that accession from CCPP, in case anyone else is interested in testing out this theory. It is listed as âtrifoliate x satsumaâ under the satsuma category, number 396, which matches the VI number in Johannâs screenshot.
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16F this year killed my satsumas. Citrus hardy to 16F means hardy for a few hours. 24 hours of 16F will kill all citrus.
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Wow, the topic of edible âcold hardyâ citrus comes up again. It has all been tried before. During the 60-80s lots of people tried crossing trifoliate orange to various edible citrus. Results were the hybrids tasted awful. Taste can be described as âcaution you arenât really being poisoned, it just tastes that way.â
Iâve tasted all the trifoliate crosses. All tasted awful.
Last citrus killing freeze in Houston was 1989. Then the Houston area the 2021 freeze of 10F killed all edible unprotected citrus, most including the rootstock. 19 of 20 of mine survived because I spent two days covering them with mulch. Week before weather was cool.
Then there is this year. Weather was spring like before suddenly 16F one night. Didnât have time to mulch citrus much and I expect 19 of 20 froze. The trees were 9 years old and most on flying dragoin. Only one tree survived with leaves, the marumi kumquat on flying dragon.
Dream all you want but I can report on yuzu. Gave a nice big one to my friend John Panzarella and he planted it in New Caney, TX about 20 miles north of downtown Houston. I expect it perished.
Conclusion: be very cautious about believing sellers of citrus who claim cold hardiness. You believing exaggerations gets them sales of tree.
I see mention of Dunston citrumello as edible. I have my doubts. Swingle citrumello taste is so bad most people wouldnât try it after just smelling the fruit. Iâve had one bite and it was awful. The smell of trifoiate orange sticks with you especially as it is difficult to wash the taste out of your mouth. It contains juice/resin that sticks to your fingers and canât be removed with water. Must use acetone to get it off. I wear gloves when harvesting trifoliate fruit for rootstock seeds.
But dream on about edible citrus in zone 7a. Your delusions cause no harm other than wasting money on trees that will freeze and produce awful fruit.
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I quote from the book âCitrus for the Gulf Coastâ by J. Stewart Nagle: Swingle citrumelo=>âfairly juicy but juice sour and very bitter with strong astringency and gum cells to carry flavor.â Morton citrange=> Although the fruit looks like an ordinary orange, it has much worse flavor. Juice cannot be diluted to obtain satisfactory flavor, but the fruit may be consumed with a grapefruit spoon , if one is careful to not scrape too many astringent oil droplets off the section walls." Citrandarin=> moderately juicy, juice with sour trifoliate-mandarin flavor, somewhat bitter and astringent. Phelps citrange=>âThe fruit should carry a warning label: Caution you are not really being poisoned - it just tastes that way.â US119 or âSnow Sweetâ=>"juicy with a moderately sweet orange flavor, but with and unpleasant, lingering bitter trifoliate aftertaste. Not as sweet as Morton citrange but more attractive and with much less âbite.â I donât know about you but I prefer citrus fruit that doesnât have a âbite.â Ichang lemon=>âvery juicy, juice sour but insipid, without much distinctive flavor.â
Havenât read a recent description of yuzuquat, a hybrid of two edible âcold hardyâ citrus. Fruit the size of kumquats, sour but little citrus flavor. I gave a large one to a friend who lives 50 miles north where it is 5 degrees colder than Houston.
Around here many people have trees of sour orange, citrange and citrumello. The top froze and the rootstock survived. Iâve collected fruit for rootstock seeds. Sour orange is at least sour but edible as a lemon substitute and makes marvelous marmalade. However as a rootstock is not great since edible citrus on sour orange are easily killed by severe freezes.
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The Prague citsuma is allegedly not a cross, but a chimera, which is interesting enough that I want to see it even if it likely will need to stay in the greenhouse for bad freezes.
I will graft it on a trifoliate outside just to test, but Iâll make sure to have one in the greenhouse as backup.
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Iâm glad you got a hold of this. It sounds very promising. Do you have enough rootstock for the scion youâve got?
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I ordered 5 buds, which I assume will be one stick. Iâm only planning 2 or 3 grafts, but figured Iâd use 2 buds for a couple of them, so doubt Iâll have extra. I maybe shouldâve gotten a few more, now that Iâm thinking about it, but oh well.
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This is the first Iâve ever heard of the citsuma Prague. How is the fruit quality? Does it have any of that trifolate taste? I donât mind sour at all, Iâm just not a fan of overpowering bitter or that distinct trifolate flavor.
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I donât believe what people tell me, I believe what I see and experience for myself. And the only way to do that is to try it. There are confirmed success of Yuzu in the Pacific Northwest. On display for anyone who want to see it is a very large unprotected Yuzu at a local nursery, covered with lovely Yuzu every fall. So thatâs what most people focus on. The ichandrin and sudachi do quite well for me, though itâs a very well protected area, not a greenhouse. The other aspect of it is just really people playing around with the science. Itâs fun to grow rootstocks and graft them and see how far you can push them. What is the big deal with that?
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