When to Apply Pre-Emergent
When to apply pre-emergent herbicide based on soil temperature, not calendar dates. Timing windows for crabgrass, foxtail, goosegrass, and winter annual weeds.
A soil thermometer costs $10 to $15 and is the most reliable timing tool for pre-emergent application. Push it 2 inches into bare soil in a sunny area of your lawn. Check daily starting in early April (Central Plains) or mid April (Upper Midwest). Air temperature is unreliable because soil warms more slowly than air.
Crabgrass and foxtail germinate when soil holds 55 degrees at 2 inch depth for three or more consecutive days. This is your spring pre-emergent window. In the Omaha metro area, this typically falls between April 15 and April 30. Apply within this window and water in within 24 hours.
Goosegrass germinates 2 to 3 weeks after crabgrass at 60 to 65 degree soil temperature. If your lawn has both crabgrass and goosegrass history, consider a split application: half the annual rate at 55 degrees, the second half 6 to 8 weeks later. This extends the barrier through both germination windows.
Winter annual weeds (henbit, chickweed, annual bluegrass) germinate in early to mid fall when soil begins cooling. Apply pre-emergent in the first two weeks of September in the Central Plains. This window is less temperature-dependent than spring because the target weeds germinate over a broader range.
Pre-emergent must reach the soil surface to form its chemical barrier. Water in with half an inch of irrigation or time your application before a forecasted rain. Without watering in, the product sits on grass blades and degrades in sunlight. This is the most common application mistake.
Recommended Products
Our tested and recommended products for this task.
