Plastic is widely integrated into modern gardening, from containers and tools to irrigation systems and row covers. While this material offers durability and low cost, plastic presents a challenge for gardeners concerned about soil health and food safety. The primary concern is differentiating between plastic types that remain inert and those that can degrade or leach chemicals into the soil and water over time. Informed selection requires understanding the material’s composition and how it reacts to environmental factors like heat and sunlight.
Identifying Plastics by Resin Code
To make informed choices, gardeners can utilize the Resin Identification Code (RIC) system, a number typically found inside a triangular symbol on the plastic item. This code, ranging from 1 to 7, identifies the specific polymer resin used to manufacture the product. These codes were developed to help recycling facilities sort materials, as different plastic types must be processed separately.
Code 1 is Polyethylene Terephthalate (PETE), and Code 2 is High-Density Polyethylene (HDPE). Polyvinyl Chloride (PVC) is marked with Code 3, and Code 4 is Low-Density Polyethylene (LDPE). Code 5 is Polypropylene (PP), Code 6 is Polystyrene (PS), and Code 7 is a catch-all for all other plastics, including polycarbonates and multi-layer materials. Knowing this number is the first step toward determining a plastic item’s suitability for a garden, especially one used for growing food.
Recommended Materials for Edible Gardens
The safest choices for direct contact with soil and edible plants are High-Density Polyethylene (HDPE, Code 2) and Polypropylene (PP, Code 5). These materials are known for their high chemical stability, meaning they are relatively inert and less likely to release additives into the surrounding environment, even when exposed to fluctuating temperatures.
HDPE is exceptionally strong and resistant to moisture and chemical solvents, which makes it an excellent choice for long-term use outdoors. Products like food-grade buckets, heavy-duty nursery pots, and durable raised bed liners are often made from HDPE.
Polypropylene (PP) is also highly recommended due to its durability, high melting point, and inherent resistance to UV radiation. This plastic is commonly used for bottle caps, food containers, and many commercially available garden pots, including vertical garden systems. PP is generally considered a safe and reliable option for containers and watering components. Both HDPE and PP are frequently stabilized to resist ultraviolet light, which slows the physical degradation that can compromise the material’s integrity over time.
Understanding Risky Plastics and Chemical Leaching
Certain plastics should be avoided, particularly when they are in direct contact with the growing medium or water for food crops. Polyvinyl Chloride (PVC, Code 3) is a major concern because it often contains significant amounts of chemical plasticizers, most notably phthalates, to make it flexible. These phthalates are not chemically bound to the plastic and can leach into the soil, where they may be taken up and accumulated by edible plants. Phthalates are a group of chemicals that have been linked to a number of adverse health issues, making PVC a material best kept away from vegetable gardens.
Polystyrene (PS, Code 6), which includes materials like Styrofoam, presents another risk due to the potential leaching of styrene, a chemical monomer used in its production. Heat, such as that generated in a compost pile or by intense sun exposure, accelerates the release of styrene into the surrounding soil or water. Polyethylene Terephthalate (PETE, Code 1), while often recycled, is not ideal for long-term outdoor use because heat and UV exposure can compromise its structure, potentially leading to the migration of chemicals.
Extending the Life of Garden Plastics and Responsible Disposal
Even the safest plastics will eventually succumb to the relentless effects of outdoor conditions, particularly solar ultraviolet (UV) radiation. UV exposure breaks down the polymer chains in plastic, causing the material to become brittle, crack, and fragment. This process is the primary source of microplastics in the garden, which are plastic particles less than 5 millimeters in size that contaminate the soil structure and can affect soil organisms.
To extend the lifespan of safe HDPE and PP items, minimize direct sun exposure by painting containers with UV-resistant paint or placing them in shaded areas. When plastic garden items reach the end of their useful life, responsible disposal is necessary to prevent environmental contamination. Thoroughly rinsing plastic pots and containers is advisable before recycling, as soil residue and chemical exposure can complicate the process. Many local recycling programs or garden centers offer specific take-back programs for used nursery pots.