Alternative Nursery Substrates for the Great Plains: Maclura pomifera

The search for sustainable, local substrate resources is active across the United States. In the Great Plains region, weedy tree species are prime targets for alternative substrate research due to a lack of native pine species. Maclura pomifera (Osage Orange) is one such species that can be found in fields, along fencelines and creekbeds. Maclura wood is highly resistant to decay, which may make it an ideal alternative substrate option for long-term woody crops. The objective of this study was to evaluate growth of redbud (Cercis canadensis) and crapemyrtle (Lagerstroemia indica ‘Arapaho’) in substrates composed of pine bark or Maclura ground to pass one of four hammer mill screen sizes (0.48 cm, 0.95 cm, 1.27 cm, or 1.91 cm).  Substrates were pre-plant incorporated with 20% sand (by volume), control release fertilizer (Osmocote, Scotts, Marysville, OH) and a micronutrient package (Micromax, Scotts, Marysville, OH). Liners were planted into 8.7 L containers and placed on a gravel nursery pad with overhead sprinkler irrigation (2.54 cm/day). The study was terminated 154 DAP (days after planting). For redbud, there were no differences in growth index ([height + widest width + perpendicular width]/3), trunk caliper, or root dry weight at 154 DAP. However, shoot dry weight was greatest in 1.91 cm Maclura and the least in pine bark. In crapemyrtle there were no differences in root dry weight, however, plants grown in pine bark or 0.95 cm Maclura had the greatest growth indices. Plants grown in pine bark had greater shoot dry weight than those grown in 1.27 cm Maclura. In many alternative substrates container capacity is low and air space is high. This occurred with the larger screen sizes of Maclura (1.27 and 1.91 cm). Pine bark used in this study had the opposite relationship with high container capacity (68.8%) and low air space (4.7%). Substrates composed of 0.48 cm and 0.95 cm Maclura remained in the ideal ranges for container capacity and air space. Results of this study indicate that Maclura pomifera may potentially make an acceptable substrate component in the production of woody nursery crops. However, more studies are needed to determine long-term status of the substrate and production protocols before widespread use in the industry can be recommended.