Native to China and Korea, this is the hardiest member of the citrus family, tolerating temperatures as low as 20F. It is also a formid- able barrier plant: stout, needle- sharp spines, 12 in. long, arm the length of its glossy green stems. Anyone planning to penetrate a hedge of hardy orange should line up blood donors first.
Dense, low-branched plant reaches 20 ft. tall and 12 ft. wide. Takes pruning and shearing into hedges very well; also good as espalier. Used as a dwarfing rootstock for many types of citrus. Glossy, dark green, 2-in.-long leaves are composed of three oblong leaflets; foliage turns yellow or yellow-green in autumn. Fragrant, 1- to 2-in.-wide white blossoms appear in spring. Sticky, aromatic (but inedible) fruit follows the flowers; it is green at first, ripening to yellowish orange in fall. Seeds from fallen fruit sprout prolifically. Easy to grow in just about any well-drained soil. 'Flying Dragon', to about one-third the size of the species, is a rather bizarre dwarf selection with twisted branches and curving, clawlike thorns.