Petroleum-based plastics are the most common materials used for greenhouse and nursery container construction. With limited opportunities for recycling, plastic containers are often destined for the landfill and present a significant solid waste issue for the green industry. In California alone, Hurley (2008) estimated that greenhouse and nursery growers disposed more than 11,800 tons of plastic trays, flats, and containers annually. As the green industry is moving toward sustainability to meet the demands of society, the use of biocontainers as alternatives to plastic containers has drawn significant attention, especially because they do not have the same disposal issues as plastic containers.
A wide variety of biocontainers are available in the market (Table 1). Biocontainers are generally classified as being either plantable or compostable (Evans and Hensley, 2004; Evans et al., 2010). Plantable biocontainers are designed to allow roots to grow through the container walls and into the surrounding soil. These containers readily decompose after being directly installed in the landscape (Evans et al., 2010). In contrast, compostable biocontainers do not decompose quickly enough to allow roots to physically break through container walls. As such, these containers must be separated from the plant at transplanting (Mooney, 2009).
Type of biocontainers used in the experiment to evaluate the impact of container type on plant performance and container decomposition under landscape conditions in five locations [University of Illinois at Urbana-Champaign (IL); University of Kentucky, Lexington (KY); Mississippi State University, Crystal Spring (MS); Texas A&M University at El Paso (TX); West Virginia University, Morgantown (WV)]. Plastic containers were used as a control.
Plants can be exposed to stresses such as extreme temperature, mechanical injury, and changes in growing environment when they are transplanted into the landscape. These stresses adversely impact plant growth and can lead to a condition known as transplant shock (Koeser et al., 2009; McKay, 1996). Proponents of plantable biocontainers suggest that their use limits root system disruption and reduces transplant shock (Evans and Hensley, 2004; Evans and Karcher, 2004).
Biocontainers have been linked to both decreased growth and increased need for irrigation in greenhouse production. Evans and Hensley (2004) reported that shoot dry weights of ‘Janie Bright Yellow’ marigold (Tagetes patula), ‘Cooler Blush’ vinca (Catharanthus roseus), ‘Orbit Cardinal’ geranium (Pelargonium ×hortorum), and ‘Better Boy’ tomato (Solanum lycopersicum) grown in feather and peat containers were lower than those grown in plastic containers. However, a greenhouse study has shown that dry weights of ‘Yellow Madness’ petunia (Petunia ×hybrida) grown in slotted rice hull and bioplastic sleeve containers matched or exceeded those of a conventional plastic control (Koeser et al., 2013). This was attributed, in part, to the relatively impervious nature of the materials used to construct the slotted rice hull containers and bioplastic sleeves (Koeser et al., 2013).
Most plantable biocontainers are made from highly porous materials (e.g., peat, wood fiber, or manure) that may provide little resistance to water loss from the root zone to the surrounding soil in the landscape (Koeser, 2013). Furthermore, it is believed that some biocontainers (e.g., peat) may wick water up out of the root zone if not sufficiently buried (Kuehny et al., 2011). ‘Cooler Blush’ vinca and ‘Dazzler Rose Star’ new guinea impatiens plants grown in feather and peat containers required more water and more frequent irrigations than those grown in plastic containers (Evans and Karcher, 2004). Evans et al. (2010) also observed that the amount of water required to produce a geranium crop was significantly higher and the average irrigation intervals were shorter for peat, wood fiber, coir, manure, and straw containers than for traditional plastic containers.
Plantable biocontainers are designed to degrade in field soil. This rate of decomposition must be slow enough to meet the needs of growers during greenhouse production, but fast enough not to impede plant establishment, root growth, and future landscape aesthetics and uses. To date, a few studies have addressed the rate at which plantable pots degrade after placement in the landscape (Evans et al., 2010). Decomposition of peat and feather containers was significantly affected by container type and the species grown in the container (Evans and Karcher, 2004). In landscape trials held in Pennsylvania and Louisiana, Evans et al. (2010) reported that manure containers had faster decomposition than peat, straw, and wood fiber containers, followed by coir containers. Evans and Karcher (2004) observed that the difference in decomposition between peat and feather containers in which ‘Better Boy’ tomatoes were planted was insignificant. However, the same study also showed that decomposition was higher for feather containers than for peat containers in which vinca and marigold were grown. To date, no studies have assessed decomposition of the more recently developed slotted rice hull and bioplastic sleeve in field soils. To address this concern, field trials of seven plantable biocontainers (coir, manure, peat, rice hull, soil wrap, straw, and wood fiber) were conducted in 2011 and 2012 at five locations in the United States with wide variability in climate to assess the impact of containers on plant performance and container decomposition.
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