Evaluation of Bioplastic-coated Fiber Containers for Greenhouse Grown Plants

Biocontainers made of coconut coir, paper, peat, wood, or other natural fibers are considered sustainable alternatives to containers made of petroleum-based plastics.  Feedstocks for fiber containers are biorenewable and biodegradable, and therefore more ecofriendly than petroleum-based plastics, but growers’ acceptance and use of fiber containers have been limited by their comparatively high cost, low strength and durability, and low water-use efficiency.  We hypothesized that coating fiber containers with bioplastics would improve their strength, durability, effectiveness, and water-use efficiency during plant production.  We dip-coated fiber containers (11.4 cm top dia.) of coir, paper, and wood with one of four bioplastics (polyamide, polylactic acid, polyurethane, or tung oil) and then compared the effectiveness of coated containers, uncoated containers made of the same three fiber types, uncoated peat-fiber containers, and injection-molded controls made of petroleum-based plastic.  Ease of coating was assessed, along with the cost and strength of containers and their effectiveness and water-use efficiency during greenhouse production of marigold, petunia, salvia, pepper, and tomato.  Subsequently, the establishment of transplants outdoors with containers removed, crushed, and installed near plant roots, and the degradation of container materials in soil were evaluated.  Polyurethane was the least expensive bioplastic and was easy to apply as an ecofriendly, water-based dip coat.  The other bioplastics required a hazardous and costly organic solvent.  Coatings of polyamide, polylactic acid, and polyurethane increased container strength and durability, and improved water-use efficiency during plant production.  Coated paper-fiber containers resisted compression better than petroleum-plastic controls.  Greenhouse-grown plants in containers coated with polyamide, polylactic acid, or polyurethane were larger and rated healthier and of better quality than plants grown in uncoated or tung-oil coated fiber containers.  Plants grown in paper- and coir-fiber containers coated with polyamide, polylactic acid, or polyurethane were similar in health, size, and quality to plants grown in petroleum-plastic controls.  Coated fiber containers degraded more slowly than uncoated containers in soil, but the degradation of container pieces near roots did not affect the establishment or growth of transplants.  Our results support the hypothesis that coating fiber containers with bioplastics can improve their effectiveness for crop production. Paper–fiber containers coated with polyurethane showed particular promise and were similar in cost and performance to containers made of petroleum-based plastic.