Besides laying claim to the coolest name we can imagine for a citrus fruit, the Yuzu, a small citrus hailing from Japan and China, is renowned for its ability to withstand temperatures as cold as 10 degrees F. In Japan, chefs use the tart fruit for quintessential condiments including the Ponzu sauce you dip your dumplings into. Growers in the US might become excited about the tree as a citrus variety that it may conceivably be possible to grow in colder climates.
Four Winds Growers in Winters, CA provides Yuzu trees for sale, as well as a brilliant fact sheet on the fruit and several condiment recipes. Three cheers for cold-hearty citrus! Three cheers for making your own outrageously wonderful condiments!