Certified Professional Horticulturist (CPH) Practice Exam

What is the ideal temperature range for composting to effectively break down materials?

1. 100-140°F

2. 50-70°F

3. 70-90°F

4. 140-160°F

The correct answer is: 100-140°F

The ideal temperature range for composting materials to break down effectively is between 100 and 140°F. Within this temperature range, microbial activity is heightened, which accelerates the decomposition process. This temperature helps to optimize the activity of thermophilic bacteria, which thrive under warmer conditions and significantly contribute to the breakdown of organic matter. At temperatures above this range, particularly above 160°F, microbial activity can begin to decline, and many beneficial microorganisms may be killed off. This can slow down the composting process and disrupt the balance of microorganisms needed for efficient decomposition. On the lower end, temperatures below 100°F may not provide sufficient heat to support rapid microbial activity and might result in slower composting, as cooler temperatures favor mesophilic microorganisms that operate less efficiently than thermophilic ones. Thus, maintaining compost temperatures within the 100-140°F range is key for effective composting, ensuring a fast and efficient breakdown of organic materials.