Professional and home gardeners alike can grow landscapes sustainably with the help of biodegradable plant containers, but gardeners may wonder whether these containers decompose quickly enough to avoid hindering plant growth.
A study conducted by University of Georgia researchers determined that, under standard cultivation practices, certain types of biodegradable containers will decompose within a single growing season.
In a recently published article in the Water, Air and Soil Pollution, UGA scientists determined how industry-standard growing practices affected the decomposition of widely available biodegradable — or alternative — growing containers. This study was led by Bethany Harris while she earned her doctorate in horticulture under the guidance of Professor Bodie Pennisi and soil microbiologist Mussie Habteselassie in the College of Agricultural and Environmental Sciences at the UGA Griffin campus.
“Under standard cultural and environmental conditions (fertilization, organic soil amendment, irrigation), alternative containers made of recycled paper, coconut fiber and wood pulp fiber will degrade in the soil within a single season,” said Pennisi.
Pennisi, a horticulture specialist with UGA Cooperative Extension, said that although alternative containers made of animal- and plant-based byproducts have been available for more than 10 years, consumers and industry professionals have been slow to adopt these environmentally friendly options.
“One of the reasons is the perception that, when annual bedding flowers are installed in plantable containers in the landscape, the container does not degrade rapidly enough by the end of the growing season and thus necessitates manual removal of remnants,” Pennisi said.
Evaluating paper, wood pulp and coconut fiber containers
The study focused on three factors involved in decomposition — moisture, fertilization and organic soil amendment — and their effects on alternative containers. Researchers examined three container types and measured the response of each to these factors.
“In our study, we chose three types of biodegradable containers — recycled paper, wood pulp fiber and coconut coir containers — due to their market availability and their varying levels of cellulose and lignin content,” said Harris, who also earned a bachelor’s degree in environmental resource science and a master’s degree in entomology from CAES.
Harris reviewed the literature of previous studies on biodegradable containers and how they were used in the horticulture and nursery industry. Then she worked with Pennisi and Habteselassie to determine the best way to conduct laboratory trials for results that could educate that industry.
Over the course of the project, the team examined soil samples with specific combinations of water content, organic soil amendments and fertilizer. They conducted three separate studies to evaluate the decomposition of each type of alternative container. Each study took 182 days, representing the length of a typical growing season for annual bedding flowers.
Researchers used control groups for each study in which soil samples without a biodegradable container received the same treatment of water content, organic amendment and fertilizer. They distinguished this study from past research by conducting the trials in a controlled lab setting rather than in the field, where other environmental factors could influence the findings. Harris said multiple factors like soil pH, container thickness and density of soil microorganisms can also contribute to container decomposition.
At set intervals throughout each experiment, researchers measured each sample’s decomposition rate using carbon dioxide traps. The more carbon dioxide released in the soil, the higher the rate of decomposition. This method offered precision and a novel approach from past studies, which assessed remaining container weight rather than amount of carbon dioxide released.
Pennisi said that her lab will expand on this research to examine container decomposition over longer periods of time. Further study of this subject in the field will enable researchers to develop best practice recommendations. Pennisi’s team plans to extend outreach about the benefits of alternative containers to increase their overall use among the public, green industry producers and landscapers.
Harris and Pennisi conducted a study in 2017 that found that both consumers and industry professionals may be unaware of the benefits of plants grown in alternative containers. They hope this new knowledge will inspire consumers to request plants grown in sustainably produced containers rather than plastic.
“Product development and research have spoken. It falls on us as consumers to actively seek plant material that has been produced in alternative containers, thereby creating the demand that will encourage the green industry to widen its use of environmentally friendly pots,” Pennisi said.
Now the director of education at Callaway Resort and Gardens, Harris directly interacts with the public and industry on a daily basis and educates them about topics of sustainability through strategic programming. She says her research and time working with Extension prepared her well for this role.
“I really learned the importance of the land-grant mission, which encompasses research, teaching and extending research-based knowledge to those in the community in which you serve,” Harris said. “At Callaway Gardens, I have had the opportunity to extend this research-based knowledge and educate the public, including visiting guests, about the use and adoption of biodegradable containers as well as other research-based topics.”
For more information on the UGA Department of Horticulture, visit hort.uga.edu.