Family: Moraceae—mulberry family Genus:Maclura Species:pomifera Common names: Osage-orange, hedge-apple, Bois d’Arc, bodark, yellow wood Mature height: 40 feet (6) Mature width: 40 feet (6) Growth rate: Rapid (6) Crown form: Arching and spreading (6) Lifespan: Up to 100 years, 75 on average (1)
Description Form Osage-orange typically takes the form of a multistemmed shrub or tree with a single stem, though the trunk is short and branches out and upward with several prominent limbs (9). The bark of the tree is thick with deep furrows and flattened brown-gray ridges that form an interwoven pattern (6). Osage-orange has very dense branches with thorns 0.5 to 1 inch in size which are retained even after they have been shaded out (10). Flowers and Fruit According to Silvics of North America (1), osage-orange is dioecious, meaning trees are either male or female. Flowers blossom from April through June, with pollen spread by the wind; the fruit ripens from September through October. Leaves Osage-orange is deciduous, meaning it sheds its leaves in the fall. Its leaves are dark green above with a waxy cuticle and are pale green below with light pubescence, meaning they have some short hairs; the leaf form is simple and alternate and the leaves may form clusters at the end of spurs alongside the flowers (9).
Region of Origin Osage-orange is native to Texas, Oklahoma, and Arkansas (1). Due to its suitability on a wide variety of sites and durable, pest-resistant wood, osage-orange has spread throughout the United States, acting as a natural barbed wire before later becoming the preferred material for fence posts on farms.
Habitat Requirements Burns and Honkala observe in Silvics of North America (1) that osage-orange “grows vigorously on all soils” and tolerates a wide range of moisture levels . Natural regeneration occurs on bare mineral soil, allowing it to spread from cultivated hedges onto pastures and fields that have experienced exposed soil through overgrazing or erosion. In this way it can sometimes become invasive. While it is tolerant of colder temperatures, it succumbs to winter-kill in the northern Great Plains. Light: Shade intolerant (1) Soil type: Any soil type, as long as it is not compacted (1) pH Level: Lower limit of 4.5 (2) with the ability to tolerate soils “too alkaline for most forest trees” (1) Moisture content: Grows best in moist soils, though tolerates drought (1) Plant Hardiness Zones: 4-9 (6)
Figure 6: The range of osage-orange in North America (6)
Figure 7: USDA Plant Hardiness Zone map. Note the upper range of osage-orange, around Pine City (7)
Wood The Wood Database (7) notes that osage-orange has ring-porous wood, meaning that within its distinct annual growth rings the pores in the earlywood are larger than those in the latewood. Osage-orange wood is highly decay resistant, both heavy and hard, and is flaxen or creamy golden yellow in color. Despite its hardness it can be easily worked, used to make archery bows, instruments, or other wood items in addition to its primary use in fence posts.
Propagation Osage-orange can be propagated through either hardwood or softwood cuttings (9). Evans and Blazich (4) explain how to successfully procure cuttings, noting that hardwood cuttings “are taken from dormant, mature stems in late fall, winter, or early spring”. Softwood cuttings are more tender and taken from the pliable new growth of woody plants in May, June, or July; one way to check if the softwood cutting will likely result in successful propagation is if its older leaves are larger than the newer leaves. A USDA publication (9) describes the preparation process after the cuttings have been taken:
“Softwood cuttings should be treated with indole butyric acid (IBA) at 5,000 to 10,000 parts per million (PPM) and placed in sand beds under mist conditions. Hardwood cuttings from previous seasons growth should be placed in a cool greenhouse and provided bottom heat (68 °F) and 5,000 to 10,000 ppm IBA quick dip to encourage rooting of the cuttings. Covering of hardwoods with an opaque poly sheet will delay shoot development. Rooting is possible in six weeks with this method.”
Evans and Blazich (4) note that a greenhouse is not necessarily required but rather “maintaining high humidity around the cutting is critical”. If access to a greenhouse is not available it is possible to cover a flowering pot with the cuttings in a clear plastic bag (figure 8); alternatively, one could use clear plastic to cover a wire frame over a plastic tray (figure 9).
Figure 8: Flowering pot in a clear plastic bag. A milk jug with the bottom removed can also be used to maintain the humidity (8)
Figure 9: Several cuttings in a plastic tray with a wire frame covered in clear plastic (9)
Planting Because osage-orange is able to grow on such a wide variety of soil types, with varying moisture regimes and pH levels, it is a very adaptable plant and is suitable for most sites (1). Per the University of Minnesota Extension (8), the general rules for planting are to prepare a planting hole that is about 1-2 feet wider than the root system in order to promote better root growth. Plants should be planted such that the very first root is within 2 inches and no more than 4 inches from the soil surface to prevent stem girdling roots. Approximately 3-6 inches of mulch should be applied in a 1-3 foot radius around the tree but direct contact between the mulch and the base of the tree should be avoided.
Pruning If pruning is required for an individual tree, Zins and Brown (11) note that it is generally ideal to prune them during late winter to limit the exposure of the wounds before the new growing season. Pruning annually in the early stages of the tree's life results in less work than if a tree goes years without pruning, as some faults can be difficult or impossible to rectify without damaging or killing the tree. Osage orange can also be pruned into a hedge in both urban and rural settings due to its dense branching form.
Figure 10: Consistently pruning trees when they are young can increase the aesthetic value of the tree as well as mitigate common issues, such as those shown above, that lead to branch failure or decay in later stages (10)
Pests and Diseases While osage-orange is attacked by some stem borers, pathogens, and other pests, cotton root rot - caused by the fungus Phymatotrichum omnivorum - is the primary damaging agent for osage-orange (1). Cotton root rot is primarily limited to regions with alkaline (pH >7.0), calcareous clay loam soils where soil temperatures can reach 82°F (3).
Human Uses Osage-orange was originally planted by farmers on the prairie due to its applications as a field hedge and windbreak (1). With the invention of barbed wire, osage-orange was still commonly planted as a source for fenceposts because it takes decades to rot (6). Chemical compounds within the wood have promising applications but are still being developed for industry use (1). Osage-orange has particular relevance in Minnesota with regards to mine reclamation due to its resistance to environmental effects and pests and its tolerance of a wide variety of soils and pH as well as moisture levels (1).
Wildlife Uses The distinctive fruit is not preferred by wildlife due to its bitter taste; however, the dense nature of osage-orange means that it can provide cover and nesting sites for both birds and animals (1).
Cultivars According to Silvics of North America (1), “A thornless cultivar, Maclura pomifera var. inermis (André) Schneid., can be propagated by cuttings or scions taken from high in the crowns of old trees, where the twigs are thornless”. This cultivar does not appear to differ in size compared to the native species, but is a much more appealing planting due to the lack of thorns.
Textual References 1. Burns, R. M., & Honkala, B. H. (1990). Silvics of North America. Washington: U.S. Dept. of Agriculture, Forest Service u.a.
2. Carey, J. H. (1994). Fire Effects Information System: Maclura pomifera. Retrieved April 11, 2018, from https://www.fs.fed.us/database/feis/plants/tree/macpom/all.html
3. Cotton Root Rot. (n.d.). Retrieved April 12, 2018, from https://plantdiseasehandbook.tamu.edu/problems-treatments/problems-affecting-multiple-crops/cotton-root-rot/
4. Evans, E., & Blazich, F. (1999, January 31). Plant Propagation by Stem Cuttings Instructions for the Home Gardener. Retrieved April 12, 2018, from https://content.ces.ncsu.edu/plant-propagation-by-stem-cuttings-instructions-for-the-home-gardener
5. ISU Forestry Extension. (n.d.). Osage Orange. Retrieved March 22, 2018, from https://www.extension.iastate.edu/forestry/iowa_trees/trees/osage_orange.html
6. Ohio DNR Division of Forestry. (n.d.). Osage-orange. Retrieved March 22, 2018, from http://forestry.ohiodnr.gov/osageorange
7. Wood Database. (n.d.). Osage Orange. Retrieved March 22, 2018, from http://www.wood-database.com/osage-orange/
8. University of Minnesota Extension. (1999). Planting and transplanting trees and shrubs. Retrieved April 12, 2018, from https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/planting-and-transplanting-trees-and-shrubs/