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Dunstan Citrumelo: Hardy Grapefruit that 'Approaches Edibility'

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  The citrumelo is an old hybrid that crossed the Trifoliate orange with grapefruit in an early attempt to produce cold-hardy, edible citrus after disastrous freezes in Florida in the late 1890s.  The first citrumelos were produced by Dr. Walter T. Swingle of the United States Department of Agriculture.  Swingle was successful in producing several citrumelo cultivars.  He found that like most 50% hybrids of mainstream citrus (already complex hybrids) with Trifoliate orange (probably a pure species), the Trifoliate characteristics dominated the offspring.  This tendency worked to the advantage of retaining cold-hardiness, but was a definite disadvantage when trying to produce a fruit that could be used for anything more than a furniture polish. The citrumelo has proven itself over time to be a very reliable rootstock for grafting, and many citrus today are still grafted on citrumelo, which provides a robust root system and good cold tolerance to the scion.  Most of these cultivars by th
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Clem-Yuz and the Quest for a Cold-Hardy, Sweet Citrus

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  Clem-Yuz 2-2 from Dr. Brown's original tree in Houston, TX. A very lemon-like Clem-Yuz from Augusta, GA. 'Yuzu Hybrid' from North Carolina An interesting class of citrus hybrids involving the Clementine mandarin was produced by the late Dr. John Brown of Houston, TX, back in the 1960s. Dr. Brown was a physician by profession but was an active and avid breeder of citrus, attempting to produce very cold-hardy, edible citrus. He succeeded in a number of areas, and some of his hybrids are just now getting the recognition they deserve. Many mainstream citrus are already complex hybrids involving two or more species of citrus, and this is true of the Clementine, which is probably a mandarin-orange hybrid (and the orange itself is probably a mandarin-pomelo hybrid). An interesting feature of citrus is that these hybrids produce seeds that are polyembryonic.   Each seed will contain two embryos, one produced sexually (zygotic), the other a nucellar clone of the seed parent.   O
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Satsuma - Worth All the Effort

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  Satsuma - Worth Every Effort The Satsuma “orange” (actually a type of mandarin) is generally considered to be the hardiest commercial citrus, and it generally lives up to its name.   It has a reputation of being reliably cold-hardy to at least 15F, and perhaps a little lower, as long as the freeze is of relatively short duration.   By short duration, I mean less than 36 hours of continuous temperatures below freezing.   During freezes of longer duration, Satsuma appears to be only as hardy as other mainstream citrus, and temperatures of 10F or below OR freezes lasting longer than 48 hours will kill an unprotected Satsuma. Having said that, it’s only fair for me to admit that I live at the absolute northern limit of possible culture for Satsuma.   My 20-year average winter minimum is about 15F, meaning that on average, I am pushing it.   In February 2003, January 2014, and December 2022, temperatures in my area were around 10F and freeze duration was 48 hours or more, meaning that a
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A Citrus that Deserves the Limelight: CiClem #10 or Golden Lime Seedlings in February 2023 Hybrid vigor: Seedling in September 2023 from seed collected November 2022 From 1996-2000, my family and I lived in Augusta, GA. Although I had been interested in citrus before then, it was during this time that I really tried to take my hobby to the next leve. Unfortunately, at this time there wasn't a lot of information available in books, which tended to focus on Florida and California. The Internet was still in its infancy, and social media hadn't been invented. Much of my initial knowledge of citrus came from Mike's catalog, and from books published many years before, such as The Citrus Industry, which detailed many of the early crosses that were made by USDA researcher Walter Swingle and others in the early years of the 20th Century. From the lost and found file: many years ago, my friend Mike Kirk owned a fantastic mail order nursery that featured cold hardy citrus. I bough
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Trifoliate Orange: Who's the Hardiest of them All? The hardiest citrus of all is the Trifoliate orange ( Poncirus trifoliata or Citrus trifoliata ). It is a deciduous citrus from central China, adapted to cold winters. In the United States, it is hardy to parts of Massachusetts west to about St. Louis, MO. In Georgia, it is hardy throughout the state, of course. It is definitely an heirloom plant and was frequently planted many years ago. The ripe fruit have a distinctive odor (which I find very pleasant) and many years ago, people picked the fruit in the fall and placed it in bowls inside. At that time, many people called the Trifoliate orange a "smell lemon." Because it was commonly planted and easy to grow in the South, the Trifoliate orange escaped cultivation and naturalized in many areas throughout the state (particularly the Lower Piedmont). Trifoliate orange is strongly adapted to floodplains, particularly those with sandy soil. In the Piedmont, it is extr
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Changsha Mandarin - Cold Hardy and Sweet Changsha mandarin is an old Chinese mandarin that has a long history in the South. It is a fairly common dooryard citrus, especially along the Gulf coast, and qualifies as both an heirloom plant and a "passalong" plant. Passalong plants are those that were commonly propagated and "passed along" neighbor to neighbor in the South before large nurseries and big box stores were common. Changsha made a great passalong plant because it grows easily from seed and can grow well on its own roots. Although Changsha, like many citrus, is polyembryonic and produces seedlings that are mostly identical to the parent, small variations in seedlings produced a class of citrus rather than a single type. So it's not unusual to find dooryard Changsha mandarins that vary somewhat in taste and habit - some trees are strongly upright (which is the type), others weep much like Satsuma; some produce fruit that can be dry and bland, others pr
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  Ichang Lemon: A Hardy, Beautiful, and Useful Citrus Ichang lemon is an ancient Chinese cultivar that has the advantage of being one of the earlier ripening cold-hardy citrus. Although its true origins are shrouded in mystery, it is thought that Ichang lemon is a hybrid between mainstream citrus (probably a type of pomelo) and a citrus species ( Citrus ichangensis) that is native to central China. There are many old hybrids involving C. ichangensis, although recent genetic research has indicated that while C. ichangensis may be involved, it is not a direct ancestor of the Ichang lemon. In any case, the cold-hardiness of Ichang lemon was recognized by early citrus explorers, and t he Ichang lemon has been grown in the Southeast for about 100 years, proving itself hardy at least to 10F and possibly lower. The tree is large (20 feet or more on the Lower Piedmont) with dark green, glossy leaves reminiscent of a grapefruit. The leaves have a large winged petiole, characteristic of hyb
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