What is the primary mechanism by which mulches suppress weeds?

• A. Increasing soil fertility to favor crops
• B. Excluding light
• C. Releasing herbicidal vapors
• D. Providing moisture to weed seeds

Answer: (B)

Mulches suppress weeds mainly by excluding light. A thick, even layer blocks sunlight from reaching the soil surface, so weed seeds and emerging seedlings can’t photosynthesize effectively. Without light, many weeds fail to germinate or stay suppressed under the mulch. Other mulch effects, like moderating soil temperature or reducing evaporation, can help, but they’re secondary to the light-blocking action. Mulches don’t work by releasing herbicidal vapors, and while moisture retention can influence weed growth, shading the soil is the primary mechanism that reduces weed establishment.