Black Soldier Fly Frass Supports Plant Growth and Reduces Nitrogen Leaching during Coleus Production

Industrial insect rearing is expected to increase as a feedstock to meet growing global food demand. This will lead to greater production of insect excreta known as frass, a nutrient-dense organic material that has shown promise as a natural fertilizer source with potential environmental benefits. In this study, black soldier fly (Hermetia illucens) frass (BSFF) was compared with a synthetic fertilizer (SF) during production of containerized ornamentals grown under greenhouse conditions. Fertilizers were incorporated into a bark-based substrate at 0, 0.1, 0.2, or 0.3 kg⋅m–3 nitrogen (N) planted with coleus (Plectranthus scutellarioides) plugs. Growth index, shoot dry weight, and leaf quality were assessed for a period of 6 weeks. In addition, coleus fertilized at 0.3 kg⋅m–3 N and a control had leachate collected and analyzed weekly for volume, pH, electrical conductivity, and nutrient losses. Black soldier fly frass was found to produce marketable coleus plants at 0.3 kg⋅m–3 N and reduce cumulative N leaching by 87% compared with coleus fertilized with SF at the same rate. Therefore, BSFF can be a suitable fertilizer source for coleus production without compromising growth and leaf quality while potentially decreasing nutrient leaching losses.