The greenhouse floriculture crop production industry compromises such commodities as flowering potted crops, perennials, and annual bedding plants. This sector of the horticulture production industry was valued at $3.83 billion for the top 15 producing states in 2009 (USDA, 2010). Most greenhouse floriculture crops are grown in containers. The container size is dictated by the length of time the crop will be in production and the desired finished plant size. For example, florist potted crops such as poinsettia (Euphorbia pulcherrima L.) and chrysanthemum (Chrysanthemum ×morifolium Ramat) require longer production times to grow and are typically grown in larger containers than annual bedding plants.
Petroleum-based plastics (plastic) are the most common materials used to fabricate containers for greenhouse crop production. Plastic is relatively strong, resists mildew and algae growth, and can be molded into a variety of shapes and sizes. However, after use, these containers are typically discarded, and this results in large amounts of waste plastic containers going to landfills. One potential solution to the large amounts of waste plastic greenhouse containers is the use of biocontainers. Biocontainers are generally defined as containers that are not petroleum-based and break down quickly when planted into the soil or placed into a compost pile.
Biocontainers are generally categorized as being plantable or compostable (Evans and Hensley, 2004; Evans et al., 2010). Plantable biocontainers are containers that allow plant roots to grow through their walls and may be directly planted into the final container, the field, or the planting bed. Compostable biocontainers cannot be planted into the soil because the roots cannot physically break through the container walls, and the biocontainers do not break down quickly enough to allow the plant roots to grow through the container walls. Instead, these containers must be removed before planting but can be placed in a compost pile to decompose in a relatively short time (Mooney, 2009).
There are many types of plantable biocontainers and some of them are described here. Composted dairy manure containers (CowPot Co., Brodheadsville, PA) are made of composted, compressed cow manure held together with a binding agent. Peat containers (Jiffy Products, Kristiansand, Norway) are made from peat and paper fiber. Paper containers (Western Pulp Products, Corvallis, OR, and Kord Products, Lugoff, SC) are made from paper pulp with a binder. Rice straw containers (Ivy Acres, Inc., Baiting Hollow, NY) are composed of 80% rice straw, 20% coconut fiber, and a proprietary natural adhesive as a binder. Wood fiber containers are composed of 80% cedar fibers, 20% peat, and lime (Fertil International, Boulogne Billancourt, France). Coconut fiber containers are made from the medium and long fibers extracted from coconut husks and a binding agent (ITML Horticultural Products, Brantford, Ontario, Canada). One type of compostable biocontainer available for greenhouse production is the ricehull container, which is made of ground rice hulls with a binding agent (Summit Plastic Co., Tallmadge, OH). These containers are available in different sizes and may have solid or slotted walls. Another group of compostable biocontainers are bioplastic containers, which are made from a bioplastic derived from polylactic acid or wheat starch that is then thermoformed into containers (OP47; Summit Plastic Co.).
Most research on biocontainers for greenhouse crops production has focused on water use, algae growth on the container walls, strength of the containers, and plant growth in the containers. Evans and Karcher (2004) found that when comparing peat, feather fiber, and plastic containers, the peat containers had the highest rate of water loss through the container walls, and both feather fiber and peat containers required more water and more frequent irrigations when growing a crop than the traditional plastic containers. When various biocontainers and plastic containers were compared, the crops grown in peat and wood fiber containers had the highest water use (Evans et al., 2010), but the frequency of irrigation and amount of water used were not significantly different among bioplastic, ricehull, and traditional plastic containers.
The percent of the biocontainer surface covered by algae or fungi has been another area of interest to researchers because algal or fungal growth was considered unattractive and could affect marketability. Evans and Hensley (2004) reported that feather fiber containers had 5.3% of their surface covered with algal and fungal growth and peat containers had 56% of their surface covered. In a similar study, Evans et al. (2010) found that 48% of the surface of the peat container was covered with algae after 8 weeks in a greenhouse. The bioplastic, coconut fiber, ricehull, and plastic containers had no algal or fungal growth on the container walls.
Container dry and wet strengths have been considered important because the containers need to be strong enough for handling, packaging, and shipping, and therefore, container strength has been extensively evaluated. Evans et al. (2010) measured the dry vertical and lateral strengths of traditional plastic and eight biocontainers and found the dry vertical strength of ricehull containers was 70 kg giving it the highest dry vertical strength of all containers tested. The containers with the lowest dry vertical strength were the bioplastic and rice straw containers. The paper and ricehull containers had the highest dry lateral strengths at 60 and 50 kg, respectively. The remaining biocontainers had dry lateral strengths of less than 20 kg. Evans and Karcher (2004) demonstrated that peat containers had higher dry longitudinal breaking strength than plastic or feather fiber containers. Evans et al. (2010) compared wet vertical strengths of various biocontainers. They found that plastic containers had a wet vertical strength of 55 kg and wet lateral strength of 20 kg. Ricehull and paper containers had wet vertical strengths of 45 and 55 kg, respectively. Ricehull containers also had the highest wet lateral strength of all the containers at 55 kg. The bioplastic, wood fiber, dairy manure, coconut fiber, peat, and rice straw containers all had wet lateral and vertical strengths of less than 10 kg. In another study, Evans and Karcher (2004) reported that the wet longitudinal and lateral strengths of plastic containers were higher than those of peat and feather containers.
Most of the research conducted on the physical properties of biocontainers has been focused on short-term crops such as annual bedding plants grown using overhead irrigation systems. However, many greenhouse crops are grown as potted florist crops that require longer production times than bedding plants and are often grown in larger containers using subirrigation systems such as ebb-and-flood benches or flood floors. Therefore, the objective of this research was to evaluate the physical properties of biodegradable containers compared with plastic containers for the production of long-term crops using a subirrigation system.
USDA2010Floriculture crops 2009 summary. NASS. Washington DC. Sp. Cr 6-1 (10)