What are to e hybrids made from and what zone and region are you in?
Make sure to click on peopleās name to see their profile info, most members include that info to avoid that question needing to be asked (and you should consider doing the same in your profile). Hereās Kuminās:
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I am aware that info is available. I find it hardly comprehensive. There is too much variability within zones even in a small area. Asking the question specifically allows the person to expound with greater detail. If they donāt like it they certainly donāt have to answer. If the problem is cluttering the thread I think a giant banner with his info is far more distracting. As opposed to the person answering, if they choose, and giving greater detail of specific information to advance the conversation.
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Iām located in zone 6b in Lancaster County Pennsylvania. The all time lowest temperature Iāve seen was in January 1994 when there were 2 consecutive mornings at -24Ā°F. This was lethal to Poncirus seedlings down to the snow height. The stems within the snow cover were fine.
These hybrids approach Poncirus hardiness, but likely donāt quite equal it.
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The origin of this group of seedlings are the survivors of a winter cold hardiness test undertaken in 2018/2019. 20,000 C-35 Citrange seedlings were started on a heated bed in April 2018 and were subsequently field planted in June of the same year.
By Autumn theyād attained up to 48" in height. They were unprotected during the winter of 2018/2019. There were several dozen survivors, some of which were weak dwarfs.
The best survivors were further propagated and are continuing their outdoor field test.
C-35 Citrange is a hybrid of Ruby Blood Orange X Citrus (Poncirus) trifoliata.
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Was this done for a university or business venture?
Thatās quite an ambitious undertaking. You tested seedling citrange and grafted specimens?
Do you have a link to any information about the trials or was this just informal personal endeavor?
Itās been a life long quest of mine after reading about Swingleās hybridization efforts. I have a horticultural background, but this effort is not in collaboration with any academic, or business venture. Depending on success, or results attained, this may change.
Thereās a rather detailed log of the efforts on the Tropical Fruit Forum under the Cold Hardy Citrus subcategory.
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The trial was initiated with seeds. The selected survivors were further propagated by grafting onto Poncirus seedlings. There are plans for 450 trees to be tested outdoors. Approximately half have been grafted, the remainder are waiting for the appropriate weather to arrive.
In regards to the outdoor trees, thereās a clear advantage for larger trees in withstanding low temperatures.
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Well itās very exciting. I look forward to reading more about it. Do you have any knowledge about the so called Prague citsuma? Iāve read several reports that the fruit quality is outstanding, having very little to no trifolate taste at all. On the downside, Iāve also read that itās a poor bearer and aesthetically unpleasant specimen with sparser foliage. Of course Iāll withhold my judgments until seeing and tasting for myself. I donāt know much about Swingleās efforts, just that many of his creations are used as rootstock.
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I donāt have it.
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As a Citrus breeder, Prague is a bit of a dead end for me. Itās likely of greater interest to a collector of cold hardy Citrus.
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I can understand that. Not something you can easily work with. But it is definitely interesting. I mean all the improved meyer lemons are a clone from that one tree brought to the US by Mr. Meyer. The fact it supposedly has such excellent fruit and is cold hardy as a Yuzu strikes a chord. Iād imagine the yuzu isnāt really than great in a zone 6. What if you put it on a trifolate rootstock?
In Southern Alabama I planted last year Shiranui, Meyer Lemon, Calamansi, Limequat, 2x88-2, and a Keraji.
Unprotected and around 14F as the low, but almost 3 days sub 32F.
Looks like one of the 88-2s and the Meyer lemon might pull through.
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Love it, this is great. Kudos to you for trying something out. Your project reminds me of the cold hardy avocado project by @swincher. I find these kind of home experiments exciting. Itās what draws me to gardening.
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I wish I could do 20,000 seedlings! So far Iāve started just over 200 avocado seeds and collected fewer than 30 grafted cultivars. Iāll be overjoyed if I manage to get to 1000 seedlings tested, but 20x that would be amazing.
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Still the same idea. Give yourself some credit. 
I am thinking that my root stock might have not been releasing enough sap yet, that I should have waited later in to the year before grafting.
Why did you not protect them? Just wanted to see what would pull through? 14 is very low for a meyer lemon to survive. You never know with plants. Some can surprise you. How old were they when they encountered the cold? Thereās a definite correlation between a citrus trees age and its ability to survive cold.