Hardy orange is native to central and northern China and the Korean Peninsula, where it’s been cultivated since ancient times for medicinal uses and as a food flavoring. In the United States, hardy orange appears in plant literature as early as 1823, when it was sold at the Prince Nursery in Flushing, New York, which was America’s first commercial nursery. William Saunders, a 19th-century botanist hired by the U.S. Department of Agriculture, popularized the use of hardy orange in the South. Saunders provided hardy orange plants to growers throughout the southern states as a robust rootstock for citrus. Eventually, hardy orange became popular in the region as an effective plant for hedgerows.
Although it’s mostly skin and seeds, this crude citrus species is valued as a protective hedge. It still holds its own as an edible ornamental, and it has a wide range of culinary uses. Northern gardeners use the hardy citrus as another tough, pest-free, edible plant for their home gardens.
Get to Know the Trifoliate Orange Tree
Growth difficulty. This citrus is surprisingly easy to grow and mostly pest-free. Generally, it can grow in a variety of soil conditions, including sandy and loamy soils, as long as the soil stays well-drained.
Taste profile and uses. Hardy orange’s fruit is a modified berry, 1-1/2 to 2 inches in diameter, and its thick skin can be either glabrous (smooth) or slightly downy. In summer, the small, green fruits will begin to develop and fill up the thorny branches. They’ll turn yellowish-orange in late September through October, and, if hardy orange is allowed to ripen after picking for a few weeks, the fruit will soften and the flavor will improve. The oranges are seedy and resinous, and although each fruit only contains a small amount of juice, they still have many culinary applications. We cut the citrus into thin slices to make a marmalade that was popular in 19th-century America. The juice and pulp can also be used to brighten up bland fruit sauces; we especially like adding slices of the oranges to a jar of honey, which gives a distinct aromatic flavor to the sweetener. Both the rind and the juice are tasty additions to a cocktail, such as a whiskey sour or a margarita. In Traditional Chinese Medicine, hardy orange is used for anti-inflammatory applications.
Plant description. In the wild, hardy orange trees can grow 6 to 20 feet high and form into a dense tangle of branches, but under cultivation, most trees reach only 5 or 6 feet in height. Hardy orange is an ornamental plant with deep-green branches that are curved and bent, armed with 1-to-1-1/2-inch wicked, green thorns. It has ovate-shaped foliage that’s around 1 to 2-1/2 inches long; the leaves are arranged in groups of three, hence its taxonomical name “trifoliate.” Since hardy orange is deciduous — the only one from the citrus family — the leaves will develop touches of scarlet and yellow in autumn before falling off. With its contorted, thorny branches, it’ll provide a dramatic ornamental display against snow, but don’t plant hardy orange near walking areas, where people might brush up against the sharp, curved thorns.
Flowers. The slightly fragrant blossoms appear in late April to early May and are produced on the previous year’s branches. The 1-1/2-to-2-inch white flowers each have around 4 to 7 petals surrounding a yellow stigma and anthers.
Pollination requirements. Hardy orange is fully self-fertile and productive, and mature specimens of the trees are often completely covered in fruit in autumn.
Site and soil conditions. Like all citrus, this plant prefers full sun to produce ripe fruit. Our tree has performed well in average soil with a heavy clay content. Indeed, some sources say that hardy orange does best in heavy clay soils as long as the planting site doesn’t contain a heavy amount of salt and isn’t permanently wet.
Hardiness. In plant literature, hardy orange’s cold tolerance is inconsistent, with some sources listing it as hardy to Zone 7 (down to 0 degrees Fahrenheit), but other sources say the tree can tolerate temperatures down to Zone 5 (down to minus 20 degrees). Our hardy orange cultivar ‘Flying Dragon’ has proven tough and resilient, surviving many long, brutal winters — with several days of temperatures down to minus 8 degrees — with little damage. However, protect small-sized trees before planting them in colder regions. Once the bark gets thicker and stronger and the root system develops after a few years, the tree will stay fairly resilient.
Fertilization and growth. Although hardy orange seems tough and grows without any help as long as it’s in average-quality soil, we’ve found that a yearly application of an organic citrus fertilizer will help the plants increase productivity. In our gardens, citrus is the one plant family that receives a commercial acidic plant fertilizer, which we give prior to the foliage leafing out and once again in midsummer.
Propagation. Hardy orange is easily grown from seed, with a high germination rate if planted while fresh. Cuttings of hardy orange can be successful, depending on the time of year, and the rate of success may increase if root hormone is applied to the bottom of the cuttings. We’ve found that the cuttings are slow to root and may take a few seasons to exhibit any noticeable new leaf shoots. Air-layering with a small bag of soil tied around a stem has also worked to produce rooted plants.
Pests and problems. We haven’t seen any major pests or problems with our tree. Our plant hasn’t produced any volunteer seedlings, but in the southern parts of the U.S., hardy orange has become an invasive species. Because of this, research its invasiveness in your area before planting, and take care to prevent it from spreading.
From ‘Flying Dragon’ Tree to Fun Citrus Hybrids
Looking to add hardy orange to your landscape? Poncirus trifoliata has a cultivar commonly found on the market as well as a few hybrids that are crossed with other species of citrus called “citrange,” although these seem difficult to find in nursery cultivation.
‘Benton’: A citrange hybrid of hardy orange crossed with Citrus sinensis that originated in Australia, reportedly hardy to Zone 7.
‘Flying Dragon’ Tree: An attractive form of hardy orange, with a contorted growth habit, curved spines, and bowed branches, that grows a little shorter than the straight species.
‘Morton’: Another citrange hybrid form of hardy orange crossed with C. sinensis. This cultivar is one of the hybrid fruits created by American botanist Walter T. Swingle around the 1890s. The tree produces larger fruit with fewer seeds than the P. trifoliata species and is rated hardy to Zone 8.
Related species: Hardy orange has always been viewed as monotypic, or the only species in its genus. A new species of this genus was discovered in the Yunnan province of China in the 1980s. Named P. polyandra, this plant is considered an endangered species.
This article is excerpted from 50 Cold-Hardy Fruits and Nuts: 50 Easy-to-Grow Plants for the Organic Home Gardener by Allyson Levy and Scott Serrano, published by Chelsea Green Publishing.