What Is Preemergent Herbicide?


Establishing a beautiful lawn requires promoting the vigorous growth of your turfgrass while suppressing unwanted weeds. One useful weapon in the war on weeds is preemergent herbicide. By eliminating weeds before they ever start, preemergents give your lawn a clean start in the early spring.

Pre-Emergent vs. Post-Emergent

With the growing number of weed control products at your local home improvement store, it's easy to become confused about what your lawn needs. Herbicides, or weed killers, are either pre- or postemergent. Preemergent products are applied while the grass and weeds are still dormant, during the late winter. Postemergent types are applied after green-up when weeds are visible.

Timing is Crucial

Because preemergent herbicide works by preventing the germination of the weed seed, it must be applied before this process begins to be effective. As a general rule, the herbicide should be applied two to three weeks before the weeds sprout. Since spring green-up and germination of seeds is regional and affected by weather patterns, check with your local extension service for suggestions about the optimum time for application.

Know Your Enemy

Identifying the type of weeds most common in your lawn can help you choose the best herbicide to treat them. Since a preemergent product has to be applied before the weeds make their debut, this will require you to think back to last season and remember which types were the biggest problem. Some preemergent herbicides are made to target all green, actively growing plants, while others only eliminate broadleaf weeds. If you're not sure how to identify the weeds present in your lawn, take a sample to your county extension office or lawn and garden center for help.

Follow Instructions

Following the application instructions for your chosen product is important both to ensure effective elimination of weeds and to protect your grass. Applying too heavily or too frequently can damage the roots of your lawn, adversely affecting its health and appearance.

Established Lawns Only

Preemergent herbicides are best used on established lawns, as they can kill all germinating seeds, even desirable ones. If you are seeding your lawn and fighting weeds during that process, a postemergent product will be more suitable.

Keywords: preemergent herbicide, weed killer, weed control

About this Author

Dana Hall McCain is a freelance writer based in Dothan, Ala., and is a a regular contributor to numerous regional publications. She writes features and columns on a variety of topics, including the outdoors, faith and health/wellness. She received a Bachelor of Arts from Auburn University in public relations/communication in 1995.