The main limiting factor for growing citrus is the lack of significant cold tolerance. The ideal temperature range for citrus is between 60- and 90-degrees F, though depending on the species and cultivar, some have better cold tolerance than others.
There are plenty of different types of citrus plants, which are usually divided into two main groups: sweet and acid types. Sweet citrus includes oranges, mandarins, and grapefruits. Acid citrus includes lemons, limes, calamondins, and kumquats. There are hybrids between the groups as well, which can make choosing difficult.
There are several cold-tolerant species of citrus. Generally considered one of the most cold-tolerant citrus trees, the satsuma, or satsuma mandarin, is hardy down to 15 degrees F when mature. Kumquats also have some of the best cold tolerance, being hardy down to temperatures around 15 degrees F. Grapefruit is another of the more cold-tolerant trees. Grapefruit is a relatively new hybrid that produces large yet flavorful fruit in both red and white flesh.
With most citrus, some winter protection is necessary to avoid serious dieback, especially during extreme cold periods. The most important part of the tree to protect if nothing else can be protected is the graft union, where the desired tree, or scion, is connected to the rootstock. If the plant dies back to the graft union, only the rootstock will regrow, leaving you with an undesirable citrus species such as a trifoliate orange or sour orange. There are varying degrees of cold hardiness for each type, so be sure to check the cold hardiness for any citrus being planted.