What effect does grass height have on weed competitiveness?

The correct choice emphasizes that taller grass can shade out weeds, which is a significant factor in managing weed competitiveness in turf and ornamental environments. When grass is allowed to grow to a taller height, it increases the leaf area that intercepts light. This shading effect limits the amount of sunlight available to weeds, which rely on light for photosynthesis. As a result, taller grass can suppress weed growth by creating an inhospitable environment for these unwanted plants, reducing their ability to germinate and thrive.

In contrast, shorter grass can allow more sunlight to reach the soil surface, which can promote weed seed germination and establishment. This relationship showcases the competitive dynamics between grass and weeds—where healthy, taller grass not only performs better in competing for resources but also reduces the overall weed population in the area. Therefore, managing grass height is an important practice in integrated weed management strategies within turf and ornamental settings.