Hardy Citrus Atlas

7b

Yellow citrus fruit hanging from garden branches

Taiwanica Lemon

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The Taiwanica Lemon (Citrus taiwanica), also called Nansho-daidai, is the only true lemon to reach an exceptional hardiness of 5°F (−15°C) on the tree, which makes it suitable for in-ground growing up to USDA zone 7b. Native to the mountains of Taiwan, it was introduced to Japan, where it naturalized in cold regions. The vigorous tree reaches 10 to 13 ft (3 to 4 m) in cultivation according to catalogs, and up to 16 ft (5 m) according to the Bosc catalog, with an upright, thorny habit, aromatic evergreen foliage, and very fragrant white blossom in spring. Its green fruits turning yellow at full maturity, medium-sized, with thick, bumpy skin, ripen in winter with a very sour, fragrant juice suggesting a natural cross between lemon and bitter orange. Tolerates snow on the tree without damage. Excellent for juice, marinades, marmalade, and Asian cooking. Graft onto Poncirus trifoliata, plant against a south-southwest wall.

Two large pale yellow citrus fruit on a kitchen island

Jokan Grapefruit

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The Jokan Grapefruit (Citrus × jokan) is the hardiest grapefruit in the world, native to Japan, where it was selected in the southern regions to combine respectable size and cold resistance. Its hardiness reaches 7°F (−14°C) on the tree, among the hardiest citrus in the inventory, making it suitable for in-ground growing up to USDA zones 7b and 8a. The vigorous tree reaches 10 to 16 ft (3 to 5 m) with a rounded habit, glossy evergreen foliage, and fragrant white blossom. Its bright orange, medium-to-large fruits (7 to 12 oz, or 200 to 350 g), with thick skin, ripen in winter and offer sweet, slightly tart flesh, less bitter than classic grapefruits, particularly pleasant fresh in a winter fruit salad. The ideal grapefruit for producing in a cold temperate climate. Graft onto Poncirus trifoliata, south wall.

A whole yellow citrus fruit and a cut half

Marunero Grapefruit

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The Marunero Grapefruit (Citrus obovoidea ‘Marunero’) is a hardy Japanese grapefruit from the southern archipelago, selected for its adaptation to cooler climates than classic Mediterranean grapefruits. Its hardiness reaches 7°F (−14°C) on the tree, among the hardiest grapefruits in the world, making it suitable for in-ground growing in USDA zones 7b and 8a. The tree reaches 10 to 16 ft (3 to 5 m) with a vigorous rounded habit, evergreen foliage, and very fragrant white blossom. Its golden yellow, large fruits (9 to 14 oz, or 250 to 400 g), with thick, rough skin, ripen in winter and offer sweet, juicy, slightly tart and fragrant flesh, milder than most grapefruits. Excellent for fresh eating, juice, and winter fruit salad. Graft onto Poncirus trifoliata, plant against a south-facing wall.

Two orange citrus fruit on a kitchen board

Kinkonshui

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Kinkonshui (Citrus × kinkonshui) is a rare hybrid obtained and selected in France by Sébastien B. from Japanese parents, to combine hardiness and fruit quality. Its hardiness reaches 7°F (−14°C) on the tree, making it suitable for in-ground growing in USDA zones 7b and 8a. The tree reaches about 16 ft (5 m) according to Pépinière du Bosc, with a compact rounded habit, aromatic evergreen foliage, and fragrant white blossom in spring. Its yellow-orange, rather large fruits (an indicative benchmark of 5 to 9 oz, or 150 to 250 g, is used in this entry), with thin skin, ripen in winter and give a tart, fragrant juice with complex notes blending mandarin and yuzu. A few seeds. A rare French selection grown mainly by collectors of citrus with Japanese ancestry. Graft onto Poncirus trifoliata for maximum hardiness, plant against a south-facing wall, in well-drained soil. An obscure citrus for enthusiasts of rare selections.

Rough yellow citrus fruit hanging on leafy branches

Tada Nishiki Yuzu

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The Tada Nishiki Yuzu (Citrus junos ‘Tada Nishiki’) is a historic Japanese yuzu selection with particularly bumpy, aromatic skin, traditionally grown in Kochi Prefecture. Its hardiness reaches 5°F (−15°C) on the tree, making it suitable for in-ground growing in USDA zones 7b and 8a. The tree reaches 10 to 13 ft (3 to 4 m) with a rounded, spreading habit, aromatic evergreen foliage, and very fragrant white blossom. Its golden yellow, round-bumpy fruits (2 to 3 in, or 5 to 7 cm), with thick skin rich in essential oils, ripen in October and November and concentrate a more intense yuzu fragrance than the classic variety, with higher productivity. The very sour juice is exceptional in zest, juice, ponzu vinegar, and niche pastry. Must be grafted onto Poncirus trifoliata to maximize hardiness. Plant against a south-facing wall, in well-drained soil, with generous winter mulch.

A historic botanical illustration of whole and sliced citrus fruit

Dunstan Citrumelo

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Dunstan citrumelo (× Citroncirus webberi ‘Dunstan’) is a hybrid between a grapefruit and Poncirus trifoliata, selected in North Carolina for its exceptional tree hardiness of 5°F (−15°C). It is one of the hardiest edible citrus, viable in the ground up to USDA zone 7b, without special wintering in favorable microclimates. The vigorous tree reaches 10 to 16 ft (3 to 5 m) with an upright, thorny habit, semi-evergreen foliage, and white spring flowers. Its fruit resemble a pale yellow grapefruit, 7.1 to 14.1 oz (200 to 400 g) with thick skin, ripen in winter and give a tart, slightly bitter juice inherited from Poncirus, useful as a refreshing breakfast juice or in marinade. Widely grown in the southern states of the United States. Double-graft onto pure Poncirus, south wall, perfectly drained soil.

Two halves of a pale yellow citrus fruit showing seeds

No. 1 Tri Voss

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No. 1 Tri Voss (Citrus ‘Tri Voss No. 1’, Poncirus trifoliata × Citrus ichangensis), also called ‘206’, is a remarkable hybrid created by the German breeder Bernhard Voss in the 20th century, crossing Poncirus trifoliata with the Ichang papeda. Its tree hardiness reaches 5°F (−15°C), classed among the citrus to plant in USDA zone 7b by Biggio and Londeix; growing it in 7a remains to be confirmed for the site and the clone. The vigorous tree reaches 10 to 13 ft (3 to 4 m) with an upright, thorny habit, semi-evergreen foliage, and white spring flowers. Its golden-yellow round fruit, medium-sized with thick skin, ripen in November and give a fragrant, tart juice that advantageously replaces lemon in cooking. Very productive and reblooming. A reference of the European hardy hybridization programs, celebrated by citrus enthusiasts. Graft onto Poncirus trifoliata.

Three pale yellow citrus fruit on a kitchen counter

Five Star Citrumelo

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Five Star citrumelo (× Citroncirus ‘Five Star’) is a more recent Floridian selection of the citrumelo, a grapefruit × Poncirus trifoliata hybrid. Its tree hardiness reaches 5°F (−15°C), among the hardiest edible citrus, making it viable in the ground in USDA zone 7b. The compact tree reaches 8 to 13 ft (2.5 to 4 m) with a rounded, thorny habit, semi-evergreen foliage, and white spring flowers. Its fruit resemble a yellow grapefruit, 7.1 to 12.3 oz (200 to 350 g) with smooth skin, ripen in winter and give a juice that is milder and more pleasant than that of the Dunstan citrumelo, with a moderate residual bitterness. Very productive. Excellent in blended juice, marmalade, or confectionery. One of the best choices for producing a table citrus in USDA zones 7-8. Graft onto Poncirus trifoliata, plant against a south-southwest-facing wall; well-drained soil is imperative.

A round yellow citrus fruit on a leafy branch

Shangjuan

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Shangjuan (Citrus wilsonii) is a wild Chinese citrus native to the provinces of Yunnan and Guizhou, a cousin of the Ichang lemon, from which it inherits its exceptional tree hardiness of 5°F (−15°C). It can be grown in the ground up to USDA zone 7b. The vigorous tree reaches 10 to 16 ft (3 to 5 m) with an upright, thorny habit, evergreen foliage with the winged petiole characteristic of papedas, and fragrant white spring flowers. Its large yellow fruit, 7.1 to 12.3 oz (200 to 350 g) with thick, rough skin, ripen in winter and give an aromatic, acidic juice reminiscent of a very fragrant grapefruit, with a zest exceptionally rich in essential oils. Used traditionally in Chinese cooking and Tibetan medicine. Its hardiness comes from its wild parent the Ichang papeda, which grows in the cold mountains of southwestern China. Graft onto Poncirus trifoliata.

Orange citrus fruit beside visibly trifoliate leaves

Morton Citrange

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Morton citrange (× Citroncirus ‘Morton’) is one of the first Poncirus × orange hybrids ever selected, created by the American USDA program in the early 20th century. Its tree hardiness reaches 5°F (−15°C), among the hardiest edible citrus, making it viable in the ground up to USDA zone 7b. The vigorous tree reaches 10 to 16 ft (3 to 5 m) with an upright, thorny habit, semi-evergreen trifoliate foliage like its Poncirus parent, and white spring flowers. Its yellow-orange fruit, 3.5 to 7 oz (100 to 200 g) with thick skin, ripen in winter and give a markedly sour juice with a sweet-orange aroma, acceptable as juice, in marmalade, or as a cocktail base. A historic reference of the American hardy hybridization program. Graft onto Poncirus trifoliata; it will take continental winters without flinching. Well-drained soil; a south wall is recommended.

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