RESEARCH 120 ppm N 100 75 Shredded 50 25 25 50 PERCENT WOOD 75 25 50 PERCENT WOOD Figure 5. Shown here is the effect of wood percentage on a whole-plant-fresh-mass. Aging the wood did improve growth slightly. are not yet known. The moral of the story: be careful when extrapolating from one plant species to another. MICROBIAL STABILITY OF WOOD A widely used indicator of the stability of compost is the biological oxygen demand (BOD). If the substrate is releasing low-molecular-weight organic compounds (e.g., phenols, terpenoids, creosote), microorganisms will grow and the substrate will consume oxygen. Our measurements indicate that fresh, moist sawdust has a BOD three times higher than four-month-old moist sawdust. Sawdust without sufficient moisture has a minimal BOD and ages slowly. Four-month-old sawdust and all seven types of shredded wood we have tested have twice the BOD of peat. This means that they have twice the microbial activity. The high microbial activity does not directly reduce plant growth, but it indicates that the low-molecular-weight compounds are not fully degraded and may be inhibiting growth. Adding fertilizer (mostly nitrogen and phosphorus) more than doubles the BOD of wood products, and they can be stabilized more rapidly 75 3 months 1 month 1 month Peat/Verm Peat/Perlite Peat/Verm Peat/Perlite 240 ppm N 100 Shredded 3 months 75 50 25 26 FEBRUARY 2019 GPNMAG.COM FRESH MASS (Percent of Controlhttp://www.GPNMAG.COM