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Why Am I Seeing Weeds After a Pre-Emergent?

By DoMyOwn staff

Wondering why you may still have weeds following a pre-emergent application? Learn how pre-emergents work and how to properly apply post-emergents to take care of existing weeds.

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Video Transcript


At DoMyOwn, we're receiving a lot of phone calls on pre-emergents and weeds popping up after people have applied those pre-emergents. 

You did a lot of hard work and you're still seeing weeds out there, but you're not alone. 

When you're applying those pre-emergents, it's going to lessen the weed pressure that you have. The less weeds that you have in the lawn, the less you're going to have to spend on post emergents to eradicate those weeds to get the lawn growing again.

Let's dive into some reasons why you may be seeing weeds even after applying a pre-emergent. So pre-emergents work on seeds. They prevent seeds from germinating in the lawn.

Usually you need to get that pre-emergent down before the soil temperatures reach 50 to 55 degrees. And if you've done that you don't have anything to worry about with summer weeds. Knowing that the pre-emergent that you put down is probably preventing spring and summertime weeds, rather than those wintertime weeds that you're seeing pop up into the lawn.  

Poa Annua for example would germinate in the fall, but you may not see it until early spring when the soil temperatures actually warm up enough. Then it actually starts actively growing and from there you see the white seed heads as it's reproducing for the next coming year.

Another example of that would be crabgrass. Crabgrass usually goes to seed around 50 or 55 degrees in the soil temperatures so that's why it's real important to get that pre-emergent down prior to that. And then it grows season long throughout the spring and summer.

Just know that a pre-emergent isn't going to work on every type of weed. Some weeds grow through stolons or rhizomes, or even a bulb that already have an established root system there. A pre-emergent is going to prevent seeds from actually germinating to establish that root system. 

When you're applying those pre-emergents, make sure that you're getting even coverage. You're double swiping the curbs along concreted areas, because that's where the soil actually cools off and warms up quicker in those areas which breaks down that pre-emergent. So when you're double swiping the curbs with a liquid application,  make sure that you're going back over it twice, and if you're doing it in a granular fashion, make sure that you have your spreader guard down to put that extra pre-emergent along that edge.

Just know that it takes time for that pre-emergent to work. It can take a good year of pre-emergents to control those weeds in the lawn. It's not going to go away overnight, it didn't show up overnight, so just be patient, this is very common. These weeds pop up, but you do need to apply a post-emergent to take care of those weeds. 

Knowing the type of weed that you're dealing with is key. That way, you can find a selective post-emergent to eradicate those weeds that are currently in your yard. Doing that... if you have a ton of weeds you may need to do a blanket application over that turf.

If you just have a few weeds here and there,  you can do a spot treatment. When doing a spot application, it's important to spray the weed itself and not spray the turf around it. Even though it's a selective herbicide and it wouldn't affect that turf, you can still stunt some of the grass around it, so to keep it all uniform you want to try and spray the weed itself and not the grass.

We've got a lot of resources to help identify those weeds. With a team of experts in addition to that, you can live chat with us, you can use our guides as reference, or you can call us and we'll try to make product recommendations over the phone. 

So let's get that lawn weed free! Don't forget to subscribe and check out our videos. We appreciate you watching.