Winter Citrus: The Hardiest Trees For Cooler Climates

Are you longing to grow your own citrus trees but afraid they won't survive your cold winter temperatures? Your concern is understandable because citrus trees are regarded as subtropical plants, which means they're not particularly cold-hardy and are happiest in temperatures between 60 and 90 degrees Fahrenheit. But, some varieties can handle the cold better than others. For cooler climates, a few different cultivars of mandarins, kumquats, oranges, and tangerines are generally more cold-tolerant than lemons and limes. However, there are dwarf varieties of the latter citrus trees available, which you can easily grow in large containers and bring indoors over winter.

If you do want to plant a citrus tree or two in your garden and you live in a cooler climate, one variety you could consider is the Satsuma mandarin (Citrus unshiu Marcovitch), with the most popular cultivar being 'Owari'  (Citrus reticulata). This particular variety can withstand cold temperatures down to 14 to 18 degrees Fahrenheit in USDA Hardiness Zones 8 through 11. The tree will produce small to medium-sized fruits that are delightfully tangy, and that mature from October to November. Another advantage of this variety is that the fruits are commonly seedless, which makes them easy to consume straight from the tree. Interestingly, this is also one of those fruits you can grow in a house or apartment.

Kumquats (Citrus japonica) are another variety that is considered quite cold-tolerant and can handle temperatures down to 16 degrees Fahrenheit in USDA Hardiness Zones 9 and 10. These trees produce small fruits from October right through to March. The fruits are a mixture of sweet and sour and are commonly used to make marmalades. For slightly sweeter fruit, try the 'Meiwa' (Fortunella crassifolia) cultivar, or if you prefer a little more tartness, the 'Nagami' (Fortunella margarita) might be your best choice. 

If you want to try growing oranges, some varieties can handle cold temperatures in the high 20s without sustaining plant damage. One good cultivar to try is the UGA Southern Frost navel orange (Citrus x sinensis 'UGA Southern Frost'), which will grow in USDA Hardiness Zones 7 through 10. You'll also find that the 'Clementine' (Citrus × clementina), 'Dancy' (Citrus reticulata), and 'Changsha' (Citrus reticulata) cultivars have very good cold tolerance. Keep in mind, though, that citrus fruits themselves will freeze at prolonged temperatures between 26 to 28 degrees Fahrenheit. If frozen, the fruit will dry out, and ripe ones will usually drop to the ground. 

For something a little different that produces excellent citrus fruits suitable for making jellies and jams, you might want to try the 'Flying Dragon' orange tree (Citrus trifoliata 'Flying Dragon'), but take heed that the fruits from this tree are much too sour to eat raw. Nonetheless, this cultivar can be grown in USDA Hardiness Zones 5 through 9 and results in a lovely spreading tree that can reach a maximum height of 20 feet. 

Although the varieties that we've identified are considered relatively cold-tolerant, if you're expecting freezing temperatures, you should still provide your trees with some protection. This is particularly important for young trees that should have their graft union covered. You can do this by just banking the soil up around the trunk, making sure to cover the graft entirely and even the lower limbs. Once any chance of frost is over, you can carefully remove the soil bank, ensuring that you don't damage the tree's bark.

For more mature trees, you may want to explore how to cover plants from frost by using things like blankets, burlap, or frost cloth. It's also recommended that the ground around the tree is watered before the freeze because moist soil is better able to absorb and conduct heat than dry soil. If you're expecting exceedingly cold overnight temperatures, you might like to put a couple of light bulbs under the protective cover to provide a little heat for your trees — but beware of fire hazards. Alternatively, simply placing a jug of hot water under the cover overnight should also provide a bit of extra warmth.