What is the purpose of a pre-emergent herbicide?

The purpose of a pre-emergent herbicide is to prevent weed seeds from germinating. These herbicides work by creating a chemical barrier in the soil that inhibits the development of weed seeds before they have a chance to emerge as visible plants. By targeting seeds during the germination phase, pre-emergent herbicides are effective in controlling annual weeds, including many common grasses and broadleaf weeds. Applying these herbicides at the right time, usually before the soil temperature reaches a specific threshold conducive to germination, is crucial for successful weed management.

In contrast, herbicides designed to kill existing weeds are typically categorized as post-emergent herbicides, not pre-emergent. Altering soil pH levels is unrelated to the action of herbicides; this process typically involves soil amendments and is focused on creating optimal growing conditions for plants rather than targeting weed control. Lastly, while promoting turf grass growth is a critical part of maintaining a healthy lawn, it is not the function of pre-emergent herbicides. Instead, the timing and application of those herbicides help in establishing a weed-free environment that indirectly supports the growth of desirable grass.