Using liquid pre-emergent herbicide on your lawn is a great way to prevent weed seeds from germinating, especially in the early stages of spring or fall. The best time to apply liquid pre-emergent is when soil temperatures consistently reach about 50-55°F (10-13°C) for several consecutive days, which usually happens in early spring. For many regions, this timing falls around March or April, just before the weeds you’re targeting, such as crabgrass or dandelions, begin to sprout. In the fall, the application is typically made in September to prevent winter annuals, like poa annua (annual bluegrass), from establishing themselves.
Liquid pre-emergent herbicides should be applied evenly across the lawn, either using a hose-end sprayer, backpack sprayer, or a professional-grade sprayer, depending on the size of your yard. It’s essential that the product is applied uniformly to avoid streaks or areas where weeds might still germinate. The application should be done on dry grass, and once applied, the herbicide needs to be watered in lightly. This watering activates the herbicide, allowing it to form a barrier on the soil surface that prevents weed seeds from sprouting. Typically, you want to water the lawn within 24 hours of applying the product, but always check the label for specific watering instructions based on the product you're using.
Timing is especially important with liquid pre-emergent herbicides. If you apply it too early, the protective barrier may break down before the weeds even have a chance to germinate. Conversely, applying it too late means weeds will already have sprouted, making the herbicide ineffective. Liquid formulations tend to offer faster soil penetration compared to granular products, but they also require precise application. Be sure to check the weather forecast and avoid applying if heavy rain is expected within 24 hours, as this could wash away the product or dilute it too much to be effective. Always follow the label on any product. It is important to read and understand the label on the product you use. Be safe, wear the proper PPE and only apply the amount allowed on the product label.