With its twisting green branches and fierce thorns, the trifoliate orange tree tends to attract attention. Gerald Klingaman of the University of Arkansas Cooperative Extension indicates that it is one of the most asked about trees in the region. As its name suggests, the trifoliate orange tree does produce citrus. However, you won't want to use it in your landscape to provide fruit--it's very sour and mildly toxic--but to serve other uses.
The trifoliate orange tree originated in Asia and, today, finds several landscaping and horticultural uses in its adopted homeland in the southern United States. The tree remains small and can serve as a shrub. Its snaking green branches are laden with long, sharp thorns. Although the trifoliate orange loses its leaves in the fall, its green branches give it an evergreen appearance that makes it appealing to some gardeners. The tree produces small, sour, inedible fruits.
Although a close relative of citrus, the trifoliate orange doesn't have extreme sensitivity to the cold, earning it another common name: hardy orange. The tree can survive drops in temperature as low as -10 degrees Fahrenheit. When choosing a site for your trifoliate orange, choose a location that receives full sun or light shade. The tree also prefers well-drained, slightly acidic soil.
In addition to the standard trifoliate orange tree, another cultivar may add extra interest to your landscape. The Flying Dragon trifoliate orange grows with especially twisting branches. Klingaman recommends carefully pruning the Flying Dragon cultivar to show off the structure of the plant.
The trifoliate orange tree serves well as a small, attention-getting garden plant. However, that is not its only use. Because the trees stay small and produce dense branches, you can also train them as shrubs and use them as hedges. The thorns deter trespassers and make the plant appear green, even after it has shed its leaves for the winter.
The cold-hardiness of the trifoliate orange makes it a desirable tree for areas too cold to grow most citrus. In fact, one of its primary uses is as a rootstock for grafting citrus trees, which provide an added measure of cold-hardiness to the highly sensitive citrus. However, as the University of Florida IFAS Extension points out, freeze-hardiness develops only when trees are exposed to low temperatures. A spell of hot weather late in the season can reduce the trees' ability to withstand extreme cold.