How does mulch help in controlling weeds?

Mulch plays a significant role in weed control primarily by blocking sunlight that weeds need to germinate. Weeds typically require light to sprout and grow, and when a layer of mulch is applied to the soil, it covers the ground and effectively limits the amount of sunlight that reaches the soil surface. This suppression of light prevents weed seeds from germinating and reduces their ability to grow, thus keeping the garden or landscaped area cleaner and less competitive for space, nutrients, and water.

Furthermore, the use of mulch not only helps suppress weeds but also adds aesthetic value to the landscape while contributing to soil moisture retention and temperature regulation. However, the primary mechanism by which mulch directly controls weeds is through its ability to obstruct sunlight, making option B the most appropriate choice for this question.