Summer weeds, like crabgrass, must have several consecutive days of soil temperatures above 55 degrees before they germinate. If the seed is near the surface of your soil, it becomes warm quickly. If it is buried deeper, it might take several weeks before the soil becomes warm enough for the germination process to begin. This is why you see weeds much earlier in the spring season around concrete driveways and sidewalks. Winter weeds, on the other hand, require several consecutive days of soil temperatures below 60 before they germinate.
How Long is Pre-emergent Effective
Pre-emergent granule will remain most effective in the soil for 45 days after application with limited effectiveness for roughly 2 to 3 months. This is why we recommend a total of 3 applications. Twice in the spring when the average soil temperature warms to 55 degrees with a follow-up application 45-60 days later; and once in the fall when the average soil temperature drops to 64 degrees.
You'd Rather Apply too Early than Late
To determine if it is too late to apply a weed preventer to your lawn, all you have to know is what the soil temperature has been for the last few days. An excellent Soil Temperature Map is available through the GreenCast Online website. Enter your location and have a look at the 5 Day Average. If it is above 55 in the spring or below 64 in the fall, the weeds have already begun to germinate and you have missed your window.
ZipLawn’s Lawn Care platform actively monitors the temperatures at your location to remove any guesswork and be sure to apply your Pre-emergent at just the right time. Click here for a Free Quote and leave your Lawn Care to us!