2017 ASHS Annual Conference

The objectives of this experiment were to quantify the effects of substrate volumetric water content (VWC) on aesthetic quality and mechanical strength of several types of bioplastic biocontainers. Seedlings of ‘Divine Cherry Red’ new guinea impatiens (Impatiens hawkeri W. Bull) and ‘Pinto Premium Deep Red’ zonal geranium (Pelargonium × hortorum L.H. Bailey) were transplanted into four types of bioplastic or petroleum-based plastic (PP) containers (control) containers (655 mL vol.) filled with soilless substrate. Bioplastic containers included: polylactic acid (PLA)-lignin (90/10; percent parent materials by mass, respectively), PLA-soy bioplastic (SP.A; 60/40), polyhydroxyalkanoates (PHA)-dried distiller’s grains and solubles (DDGS; 80/20), and PLA-SP.A-BR (modified DDGS; 50/30/20). Plants were watered to container capacity at transplant, allowed to dry down over ~7 d to thresholds of 0.20 or 0.40 m³·m^–3 VWC, at which they were maintained by a capacitance soil moisture sensor-controlled irrigation system. Data were collected six (geranium) or seven (new guinea impatiens) weeks after transplanting seedlings, including widest and perpendicular width, height, and shoot dry mass (SDM); growth index (GI) was calculated. Container aesthetics were rated on a scale of 1–5 (1 being lowest, 5 being highest) based on discoloration relative to unused containers, and presence of microbial growth. Vertical and horizontal wet strength of containers were also quantified. New guinea impatiens GI, SDM, and vertical strength were affected by VWC. Plants grown at 0.40 m³·m^–3 VWC had 14% larger GI and 25% higher SDM than those grown at 0.20 m³·m^–3, but vertical wet strength of containers was 12% lower for containers maintained at 0.40 m³·m^–3 compared to 0.20 m³·m^–3. Horizontal wet strength was only affected by container type, and was greatest for PLA-lignin containers (0.34 MPa) and lowest for PLA-SP.A-BR containers (0.01 MPa). Container type and VWC interacted to affect aesthetic ratings of new guinea impatiens containers. Aesthetics of PLA-SP.A-BR containers were rated lowest compared to PP containers at both VWC levels; however, PLA-SP.A-BR container ratings at 0.40 m³·m^–3 VWC were 78% lower than PP containers compared to those maintained at 0.20 m³·m^–3 (46% lower). Similar trends were observed among GI and SDM of geranium, as well as aesthetic quality ratings and vertical and horizontal container strength. Producers can effectively maintain aesthetic quality and strength of bioplastic containers manufactured with higher proportions of bio-based fillers such as PLA-SP.A-BR containers by reducing substrate VWC during crop production.