804 Aleurites fordiiCommon Names: tung tree, tung oil tree, China wood oil tree, tung nut tree, aceite chino, Chinawood tree Family: Euphorbiaceae (spurge Family)
Tung is a gracefully spreading round-crowned deciduous tree that may grow to 30-40 ft (9.1-12.2 m), but usually stays half that size. The smooth brownish-gray branches arch and fork with a tropical flair, bearing alternate heart-shaped 3-5 in (7.6-12.7 cm) dark green leaves on long reddish petioles. The leaves never quite unfold all the way and have deeply incised veins that make them look almost pleated. Young trees may have larger, flatter leaves with three pointed lobes. The sap is milky white. The flowers open before the leaves come out in early spring, decorating the bare branches with eye catching ruffly looking clusters of pale peach-colored blossoms. Examined closely, the 1.5 in (3.8 cm) blooms resemble those of a catalpa Catalpa bignonioides. They have 5-7 round tipped ivory petals delicately streaked with rust-orange in the throat, creating a color effect reminiscent of peach ice cream. They are borne in long-stemmed clusters consisting of about 60 flowers. On most trees, all but one in each cluster are staminate male flowers. Upon pollination by honeybees, the female flowers develop into 2-3 in (5.1-7.6 cm) hard roundish green or purplish-green fruits that may contain 1-15 nut-like seeds, but usually have about five. They ripen in the fall as the foliage turns creamy yellow. The closely related candlenut tree (A. molucanna) has petals less than 0.5 in (1.3 cm) long and fruits with just 1-2 seeds.
Tung, Aleurites fordii, comes from the rocky subtropical foothills of western China. It is cultivated in China, Argentina, Paraguay, and, to a much lesser extent, Africa and the southeastern United States. There are naturalized populations around abandoned commercial tung oil groves in the vicinities of Tallahassee, Gainesville, and Marianna, Florida; Bogalusa, Louisiana; and Poplarville, Mississippi.
CultureTung prefers slightly acidic loamy light to medium soils. The ideal pH is somewhere around 5.5-6.0. Tung will tolerate more alkalinity, but it is likely to exhibit leaf roll and leaf scorch when the pH gets up past 7.0. A wide range of soils is acceptable, so long as it is well drained, penetrable, and deeply aerated, but still has good moisture holding capacity. Tung trees do not handle competition well. Each tree likes to have its own space out in the open. In commercial groves, they are planted at 12-15 ft (3.7-4.6 m) intervals in rows 30-40 ft (9.1-12.2 m) apart and care is taken to control weeds beneath the trees. The trees will branch too close to the ground unless excess buds and branches are removed from the saplings to force growth into a selected leader. Suckers may also require removal. Since the blossoms are borne on the ends of the growing shoots produced the previous season, ornamental tung trees should be pruned immediately after flowering. The tops of nursery liners should be cut back to 8-10" when they are set out. Early spring application of organic soil amendments and fertilizing with 6-6-6 in April and September is recommended for established trees. Seedlings respond better to a fertilizer with more potassium and less phosphorus. Micronutrients seem important. In the United States, the average life span of a tung tree is 30 years. Tung trees usually begin bearing fruit when they are 2-4 years old and reach maximum productivity at around 10-12 years. Tung fruits mature and drop to the ground between late September and early November. If they are to be harvested for oil, they should be left there until hulls are dead and the fruit's moisture content has dropped below 30 percent. This usually takes 3-4 weeks, but the fruits can lie on the ground until spring without deteriorating. Light: Nearly full sun is necessary for good growth. Moisture: Tung can take drought, but it does much better in reliably moist soil. Hardiness: USDA Zones x - x. Although the buds and succulent new growth are susceptible to frost damage, hardened-off trees can withstand freezes down to 18 ºF (-8ºC) or lower. Tung grows best where summers are long and hot and temperatures are consistently warm day and night throughout the growing season, but they still require some winter chilling. 350-400 hours below 45ºF (7.2ºC) each winter is ideal. In more tropical climates, the trees tend to produce suckers from the main branches. A hillside site with good air drainage limits freeze damage during cold spells. Propagation: Seedling tung trees typically outgrow those that are vegetatively propagated, but because tung trees grown from seed are extremely variable and often bear little resemblance to the parent plant, budding is the preferred method of propagation. Buds from a selected mother tree are inserted into the stem of a one-year-old seedling 2-3 in (5.1-7.6 cm) above the soil surface. Later, the original seedling top is cut off and the transplanted bud is grown into a new leader. Budding is best done in late August, by the simple shield method, which requires that a piece of budstock bark (including a bud) be fit into a T-shaped cut in the seedling bark. Soil should be mounded over the buds to protect them from cold the first winter. When the tree is ready to start growing in the spring, this extra soil should be raked away from the stem and the original stem should be cut back to within 1-2 in (2.5-5.1 cm) of the new bud. Cuttings of mature wood may also be rooted in a coldframe. If seeds are to be used, the nuts should be hulled and planted within a few months after they mature, since they lose viability quickly in storage. Soak them in water for 5-7 days, then plant them where they are to grow. Alternatively, seeds may be sown in a warm greenhouse in the very early spring to produce transplants to be set out late the following spring. Germination takes at least two months. If the trees are started outdoors, a summer side-dressing of 5-10-5 with zinc sulfate is recommended.
Tung was formerly cultivated primarily for its oil, but it also makes a lovely ornamental tree. The oil pressed from tung seeds makes an exceptionally fine wood finish. Often sold under the name "teak oil", tung oil dries quickly to form a tough, glossy, waterproof surface. Tung oil is also used as a drying agent for paints and varnishes; as waterproofing for paper, cloth, and ceramic products; and in the manufacture of linoleum, oilcloth, inks, resins, artificial leather, lubricants, brake linings, and cleaning and polishing compounds. It is used in coatings for food containers and electronic parts. During World War II, the Chinese developed a way to process tung oil to supplement gasoline for motor fuel. Legend has it that their ancestors used it to seal the Great Wall. Although it is dangerously toxic, tung oil has been used to treat skin conditions and constipation. Tung extracts have recently shown potential as termite control compounds.
Tung is a wonderful all-season ornamental tree. It never fails to attract attention with its glorious masses of spring flowers. The spreading umbrella form and big leaves are marvelous for summertime "tropicalismo" effects. The foliage turns yellow in the fall. And the sculptural forms of the arching gray branches are interesting in the winter.
All parts of tung tree are toxic, but the fruits are most dangerous. Eating even one seed may be fatal. Symptoms may include severe stomach pain, vomiting, diarrhea, weakness, slowed breathing, and poor reflexes. The leaves give some people a poison-ivy-like rash. The Plant Conservation Alliance categorizes this species as an Alien Invader and it is listed as a Category II invasive exotic species by the Florida Exotic Pest Plant Council. This means that it has "shown a potential to disrupt native plant communities." Although this ranking suggests that tung tree is capable of naturalizing and should not be allowed to spread into the woods, experience has shown that it does not compete aggressively. Tung trees have soft wood that is easily shattered by strong winds, so they should not be planted too close to buildings.
Linda Conway Duever 8/13/00; updated 3/24/04, 3/30/04