Biocontainers

Vinca growing in the landscape study to evaluate plantable biocontainers.

The most recent report by the USDA estimated the wholesale value for bedding and garden plants at $6.5 billion. Most containers for these crops are composed of plastic, which present a considerable disposal issue for both consumers and the horticulture industry. Numerous biodegradable alternatives have been developed. To learn more about the types and physical properties of biocontainers please see “Biocontainers Physical Strength and Biodegradability” in the September 2010 issue and “Biocontainers Water Requirements and Growth of Algae and Fungi on Container Walls” in the May 2011 issue of Greenhouse Management.

To determine the suitability of these biocontainers as a replacement for plastic containers, a comprehensive study was undertaken at Longwood Gardens in Pennsylvania, Louisiana State University and University of Arkansas. Researchers evaluated greenhouse and landscape growth of geranium ‘Score Red’, vinca ‘Grape Cooler’ and impatiens ‘Dazzler Lilac Splash’ grown in plastic and various types of biodegradable containers. The containers tested are listed in Table 1 and shown in Figure 1.
 

Greenhouse performance
At all locations, plants were grown from plugs at the beginning of April with a heating set point temperature of 68°F and a greenhouse venting set point of 83°F. Plants were fertilized at each irrigation with 200 ppm 15-5-15 Cal Mag. Since the biocontainers tested varied in size, smaller containers were filled with 400 ml of substrate and larger containers were filled with 700 ml of substrate. For each filling volume, a 4- or 5-inch plastic container was used as the control treatment. Plants were grown to a marketable size and evaluated for root and shoot dry weights, which are shown in tables 2 and 3.

Root weights of all three species of plants tested were relatively unaffected by container type. Occasionally, plants grown in one type of container produced roots that weighed more than roots of plants in other containers, but these results were not consistent across all species tested.

When geraniums were grown in 4-inch containers, those produced in paper and plastic had the highest shoot weights, and those grown in cocofiber and peat containers weighed the least. In 5-inch plastic containers, Geraniums weighed the most plastic containers and the least in Strawpots. Shoot weights of both impatiens and vinca grown in 4-inch containers were highest in paper containers and lowest in cocofiber. When impatiens and vinca were grown in 5-inch containers, those in OP47 containers had the greatest shoot weight. Although there were differences in weight between the plants grown in different containers, visually these differences were not recognizable for all three species tested. All plants in the experiment were considered marketable, which indicates that all container types tested would serve as suitable replacements for plastic when considering plant growth.

Figure 1. Vinca growing in all containers tested.

Landscape performance
Marketable bedding plants produced in the greenhouse study at Longwood Gardens and Louisiana State University were planted in raised landscape beds in full sun for eight weeks to test field performance. Only plants grown in plantable biocontainers were used in this study. Plantable biocontainers are to be left intact on the rootball and planted into the field, landscape bed or final container. This category of biocontainers is designed to allow roots to grow through the container walls and to decompose after being planted. Plants grown in 4-inch plastic containers were used as the control for the field study and the containers were removed prior to planting.

Across all three species tested, no one container type stood out as the most or least beneficial for plant growth in the landscape. Again, there were no visual differences between plants in each container type. It was thought that if a certain type of plantable containers reduced root growth due to the barrier created by the container wall, shoot growth would also suffer. This was not the case as roots easily grew through the walls of all direct plant biocontainers tested.

There was some minor variation in growth of geranium, impatiens and vinca in the greenhouse and in the field in this study. However, plants grown in all of the containers tested produced marketable plants for retail and successful landscape plants. Growers and landscapers should be aware that differences in growth can occur when using different containers. In this study, all biodegradable containers evaluated would serve as suitable replacements for petroleum-based plastic containers in the greenhouse and landscape.
 

Matt Taylor is a research horticulturalist at Longwood Gardens in Kennett Square, Pa. Reach him at mtaylor@longwoodgardens.org. Michael Evans is a professor at the University of Arkansas in Fayetteville, Ark. Reach him at mevans@uark.edu. Jeff Kuehny is a professor at Louisiana State University in Baton Rouge, La. Reach him at jkuehny@agcenter.lsu.edu.