Clay pots and commercial food cans were the first types of containers used for nursery production. Plastic containers eventually replaced the clay pots and “cans” and have become the industry standard as they are lightweight, inexpensive, and durable. Although plastic containers can be reused or recycled many times, they are not. With the move to increase sustainability in the Green Industries, many types of alternatives for petroleum-based plastic containers are being explored for use in container production. Alternative containers can generally be categorized into one of three groups: plantable, compostable, and recycled plastic/bio-based plastic containers (R3 containers), and are based on the degradation of the container after production and/or landscape installation. An understanding of these characteristics is needed for best use and selection of alternative containers in production, retail, and landscape settings.
Types of Containers
Plantable containers are designed to stay intact during short-term production (3-12 months depending on the climate, production practices, and container) and can be kept on at planting. They are designed to allow roots to grow through the walls of the pot as it decomposes in the landscape. The rate of decomposition for plantable pots is influenced by weather, soil type, and irrigation. These containers are made from natural materials such as peat, cow manure, rice hulls, rice straw, wood pulp, coconut coir, or paper.
Compostable containers are meant to be removed at planting and are made from materials that are either “backyard compostable” or “industrial compostable”. Industrially compostable containers need specific and consistent conditions to break down that don’t typically occur in normal backyard compost piles. These containers can be made from rice hulls, recycled paper or cardboard, poultry feathers, bamboo, or other natural fiber waste products. Some types of compostable containers, such as molded fiber and rice hull containers, are available in sizes for production of larger nursery crops.
Recycled plastic/bio-based plastic containers (R3 containers) are made from recycled plastics and can be blended with biodegradable natural fibers such as cotton, jute, vegetable fibers, or bamboo. These containers, similar to plastic containers, can be reused or recycled and some will disintegrate over time. Fabric containers are an example of this type of container. Recycled plastic or bio-based plastic containers can be available in large sizes for nursery production.
Some of the questions that arise with these alternative containers are:
1) How do they hold up in production, retail, and landscape settings?
2) What is the impact on water use and plant growth?
3) How do the containers perform after planting (do they break down or compost as intended)?
4) What is the additional cost of alternative containers?
Container Durability and Strength
The strength and durability of alternative containers varies with container material and production method. Plantable containers are best suited for short-term production crops such as bedding plants, vegetables, and short-cycle production. Compostable and R3 containers are normally stronger than plantable containers and are better for longer term production, with both performing well in production cycles up to one year. When considering use of compostable containers or R3 containers for production, trials should be performed prior to adoption, as durability can differ due to location as a result of growing conditions. Irrigation frequency and volume is a major factor in durability.
Plant Growth and Water Use
Plant growth and water use of plants in alternative containers can vary from that of those in plastic containers due to the physical properties of the alternative containers. For example, many alternative containers have porous sidewalls, which impacts water use, root growth, and substrate temperature, all of which impact plant growth. In general, research has shown that plant size and health can be similar or better for plants grown in alternative containers. The porous walls of plantable containers can also be an advantage as it can reduce circling roots (because roots can grow through the containers).
The porous sidewalls along with the lighter color of many alternative containers can result in cooler root zone temperatures. The lighter color means the containers absorb less heat from the sun than black plastic containers. This can be an advantage during the hot summer months, especially in the South. In northern areas, lower substrate temperatures can slow early-season growth in the spring.
The porosity of the containers can make a large difference in water use due to increased water loss through the sides of the pots. Some plantable pots can require 1.4 to 2.6 times more water compared to plastic containers (Cypher and Fulcher, 2015a). Pots made of bio-plastics and some types of compostable containers (such as solid rice hulls) had similar irrigation requirements to black plastic pots. Temperature differences due to container types can also impact water requirement. In general, alternative containers require more frequent and/or higher volume irrigations.
Research has found that, in general, plantable containers do degrade in the landscape and do not impact plant establishment. The rate of container degradation is impacted by many factors, including container type, soil type, pH, plant type, soil moisture, and soil microbial activity.
It is very important to be aware that compostable containers may not break down quickly in a home or nursery compost pile and that additional effort such as cutting up or grinding the containers can improve degradation. Many of these containers do not decompose but will eventually break into smaller pieces.
A challenge with plantable containers is that they are meant to degrade over time, which means that degradation is possible while plants are still in production or in a retail setting. Some plantable containers such as peat, manure, and some coir containers can have mold or algal growth that can be unappealing to consumers and may impact sales. Variable drying rates of substrates between container types should be taken into account in a retail setting to avoid over- and under- watering when container types are mixed in sale areas. Compostable containers can sometime look like plantable containers or even plastic containers, so it is important to understand what type of container you are working with. Plantable containers can be beneficial for landscapers due to saved time at installation from not removing containers and from saved cost of container disposal.
Some of the main drawbacks for growers are the cost of the alternative containers, which can be 10 to 50% greater than plastic pots, and increased water use/irrigation frequency due to the porous nature of some of the alternative containers. Most times, the additional cost of the container can be recovered at sale, as many consumers are willing to pay extra for more sustainable alternatives.
More information on specific containers can be found at:
Chappell, M. and G.W. Knox. 2012. Alternatives to Petroleum-Based Containers for the Nursery Industry. University of Georgia Extension.
Cypher, Q. and A. Fulcher. 2015a. Beyond Plastic Pots, Part 1: Compostable, Plantable and Other Containers for Nursery Crop Production. University of Tennessee Extension.
Cypher, Q. and A. Fulcher. 2015b. Beyond Plastic Pots, Part 2: Compostable and R3 Containers for Nursery Crop Production. University of Tennessee Extension.
Cypher, Q. and A. Fulcher. 2015c. Beyond Plastic Pots, Part 3: Plantable Containers for Nursery Crop Production. University of Tennessee Extension.