Certified Professional Horticulturist (CPH) Practice Exam

What type of organic material cannot be composted?

1. Pasteurized or heat treated

2. Dyed

3. Printed with a petroleum-based ink

4. Polymerized

The correct answer is: Polymerized

The type of organic material that cannot be composted is polymerized material. Polymerization refers to a chemical process where small molecules (monomers) combine to form long chains or three-dimensional networks (polymers). This process results in substances that are often synthetic, such as plastics or resins, which do not break down naturally in a composting environment. Therefore, polymerized materials are not suitable for composting as they do not decompose into organic matter that can contribute to soil health or support plant growth. In contrast, pasteurized or heat-treated materials, while they may be discouraged in some composting systems, can eventually break down given proper conditions. Dyed materials can be composted if the dyes are plant-based or otherwise non-toxic. Printed materials with petroleum-based ink may also be composted, but caution is warranted, as the ink may contain harmful substances that do not contribute positively to compost quality. Overall, polymerized materials stand out as they are designed to resist decay and remain intact rather than contribute to organic processing.