What is Pre-Emergent Herbicide and How Does it Work?

Weed control is an important aspect of lawn care that every property owner should be mindful of. Weeds not only take water, nutrients, and light away from other plants; they also prevent harvests from growing into their full bounty, spelling disaster for farmers and small-time gardeners. Using a pre-emergent herbicide around your property could stop these territorial plants from overtaking your home’s most valued green space.

Pre-emergent herbicide is a type of weed killer that prevents weed seeds from sprouting. Unlike normal herbicide, it is meant to stop weeds from growing in the first place by spraying or spreading a chemical onto the soil so that weeds have difficulty placing down their roots. 

Pre-emergent herbicide should not be used in areas where seeds are being planted for other plants. Although this seems obvious, many people are unaware that pre-emergent herbicide does not distinguish between weed seeds and the seeds of desired plants. Spreading pre-emergent herbicide where you want plants and flowers to grow will kill those seeds as well as those of weeds.

When to Use Pre-Emergent Herbicide

In order to make the most of pre-emergent herbicide, it should be applied before the season changes, particularly before the spring and fall arrive, which is when weeds are most abundant (winter and summer weeds also exist, although mostly in warmer climates). It can also be applied to a new garden bed or lawn one month after the seeds have been planted. This is so that plants have time to root without being compromised by the herbicide.

Most forms of pre-emergent herbicide should last around 4-6 months, or per season, before it needs to be reapplied.

How to Apply Pre-Emergent Herbicide

There are a few different forms of herbicide that you can choose from. Pellets and liquid forms are among the most common, and typically come prepackaged for ready-use. 

Pellets are placed around the soil through a rotary or drop spreader, where water is applied to activate the ingredients of the herbicide. This is called “watering in”, and needs to be completed on a dry day for the best results. In some cases, this can also be used to kill existing weeds, as its roots absorb the soil laden with dissolved pre-emergent herbicide. 

Liquid forms often come packaged in spray bottles with a hose attachment that make them easy to use. It is applied by watering it on the lawn before a few days of consistent sunshine is predicted. Many liquid pre-emergent herbicides contain a combination of active ingredients that work against weeds. Some forms may not target existing weeds, which means they need to be pulled manually before the herbicide can work. 

The weed and feed combination of pre-emergent herbicide is another option property owners can use to combat weeds. Here, fertilizer is combined with a pre-emergence weed treatment to prevent weeds from growing. This tends to work in some areas of the country, but not others. It largely depends on the timing in which it needs to be fertilized, and then be processed with weed control.