Effect of alternative containers on plant production
While biocontainers can reduce waste going into the landfill, that is only one of many environmental and economic aspects that may change as a grower transitions from conventional plastic pots to alternative containers. Past and ongoing research has documented differences and similarities regarding plant growth, plant quality, water requirements, mechanized production success, transplant shock, and a variety of container-related physical attributes. This section summarizes the current knowledge and potential issues associated with production and postproduction biocontainer use.
Plant growth and quality.
Positive and negative impacts of using biocontainers compared with plastic containers have been reported on plant growth and development during production or establishment into the landscape. At the Center for Applied Horticulture Research (CAHR, Vista, CA), tomato (
Solanum lycopersicum) plants grown in plastic containers had greater shoot dry weight than plants grown in wood fiber (Fertil Pot/DOT Pot; Fertil International, Boulogne-Billancourt, France), decomposed cow manure (CowPot; East Canaan, CT), and coconut coir pots but not different from plants grown in recycled paper (Western Pulp; Corvallis, OR) containers (
CAHR, 2009). Root dry weight was greater for plants in plastic containers compared with all other container types. When planted in the field, recycled paper and coir containers degraded more slowly than Fertil Pot/DOTPot and CowPot. ‘Midnight’ (Dreams) petunia (
Petunia ×
hybrida) grown in bioplastic (SoilWrap) and slotted rice hull (NetPot; Summit Plastic Co., Akron, OH) containers had a larger growth index compared with plants grown in plastic pots; whereas, plants grown in bioplastic (Terra Shell/OP47, Summit Plastic Co.), coir, and plastic pots were not different (
CAHR, 2010). Petunia flower number was not different during production or postproduction for plants grown in bioplastic (SoilWrap), rice hull (NetPots), and coir containers compared with plants in plastic control containers (
CAHR, 2010). Similarly, recycled paper, peat (Jiffy-Pot; Jiffy International, Kristiansand, Norway), bioplastic (Terra Shell/OP47), rice straw, cow manure, coconut coir, and rice hull container types produced marketable transplants [‘Score Red’ geranium (
Pelargonium ×
hortorum), ‘Dazzler Lilac Splash’ impatiens (
Impatiens wallerana), and ‘Grape Cooler’ vinca (
Catharanthus roseus)] within the same time frame (
Kuehny et al., 2011).
Kuehny et al. (2011) also investigated shoot dry weight of ‘Dazzler Lilac Splash’ impatiens produced in 4- and 5-inch biocontainers at three sites. For the 5-inch size containers, there was no difference in shoot dry weight at any location. For the 4-inch size, no container type was superior for all measurements (root and shoot dry weight and root:shoot ratio) at all three locations. Following greenhouse production, plants in plantable containers were installed in the Longwood Gardens (Kennett Square, PA) landscape and generally performed no differently than plants produced in plastic containers (
Kuehny et al., 2011).
‘Eckespoint Classic Red’ poinsettia (
Euphorbia pulcherrima) plants grown for 12 to 16 weeks in recycled paper (Western Pulp) containers under greenhouse conditions were reported to have increased root and shoot dry weight, plant height, and bract area index compared with plants grown in straw (StrawPot; Ivy Acres, Baiting Hollow, NY), composted cow manure (CowPot), coconut coir, rice hull (NetPot), wheat starch-derived bioresin (Terra Shell/OP47), plastic, and sphagnum peatmoss and wood pulp (Jiffy-Pot) containers (
Lopez and Camberato, 2011). In an experiment using ebb-and-flood irrigation, shoot dry weight of ‘Rainier Purple’ cyclamen (
Cyclamen persicum) grown in bioplastic, solid rice hull, slotted rice hull, recycled paper, peat, cow manure, rice straw, and coconut coir containers for 15 weeks was greater than for plants grown in plastic containers (
Beeks and Evans, 2013a). A 3-month study showed no negative impact of plantable containers [bioplastic (SoilWrap), paper (Ellepot) and slotted rice hull] on root and shoot development of two sedum species (
Sedum hybridum ‘Immergrunchen’ and
Sedum spuricum‘Red Carpet Stonecrop’) and ‘Big Blue’ liriope (
Liriope muscari) during production in a quonset and in the landscape (
Ingram and Nambuthiri, 2012).
Water use.
Evans and Hensley (2004) found that peat containers wicked water from the substrate causing ‘Janie Bright Yellow’ marigold (
Tagetes patula), ‘Cooler Blush’ vinca, and ‘Orbit Cardinal’ geranium plants to wilt. Plants grown in peat (Jiffy-Pot) containers had the lowest shoot dry weight of all three container types, whereas plants had the greatest shoot dry weight when grown in plastic containers followed by plants grown in poultry feather containers. Tomato seedlings grown in corn/palm-derived biocontainers had reduced biomass compared with those in plastic containers (
Sakurai et al., 2005a). Further, seedlings in biocontainers had slower initial establishment in the field compared with those grown in plastic containers (
Sakurai et al., 2005b). The researchers attributed this to inadequate irrigation and temporary root restriction of plants grown in biocontainers (
Sakurai et al., 2005a,
2005b). Plant biomass is sometimes greater when plants are produced in alternative containers, but in other research, plants produced in conventional plastic containers have greater growth. The inconsistency may be due to increased potential for water loss through biocontainer sidewalls and related factors, which are the subject of this section.