Do not mow for at least 5 days before spraying weeds. Then, wait 2 days after spraying before you mow your yard. Weed killers work best when weeds have plenty of leaves. This is because systemic herbicides are absorbed through the leaves. Then, they attack and kill the entire weed down to the root. If you mow before spraying for leaves, you get rid of leaf material and make your weed killer less effective. Spray, wait 2 days for the weed killer to be absorbed, then mow.
Table of Contents
How Many Days Should You Avoid Mowing Before Spraying Weeds?
If you’ve just mowed your lawn, wait 5 days before you use a weed killer spray. This will give time for weeds to grow new leaves. The weed killer will then infiltrate the plant through the leaves and get to work killing it.
- Wait minimum 5 days after mowing your yard before you spray for weeds.
- Weed killers need to be absorbed through the leaves and recently mowed weeds don’t have many leaves.
- A weed that has just been mowed is far more likely to survive being sprayed with herbicide.
It may seem strange to spray weeds when they’re at their strongest, but the best weed killers must be absorbed through the leaves. So, the more leaves the weed has the better the herbicide will work. A weed that has just been mowed or weed-whacked won’t have many leaves, so the weed killer may not kill it.
How Long Should You Wait to Mow After Spraying Weeds?
Once you’ve sprayed the weeds in your yard, wait at least 2 days before mowing. As a rule of thumb, most herbicides need a couple of days to enter the plant through the leaves, work their way down the stem, and begin attacking the roots of the plant.
- Allow 2 days after herbicide lawn treatments before you mow.
- Herbicides need 24–48 hours to enter through the leaf surface and begin to kill the weed.
- Mowing too soon may make your weed killer ineffective and allow the weed to survive.
Although most weed killers are rainfast (waterproof) after a few hours, it takes time for the herbicide to be transported through the leaves. By waiting a few days after application before you mow, you maximize the chances that the weed killer will get the job done.
Should You Mow Before Applying Pre-Emergent Herbicide?
Unlike post-emergent herbicide sprays that kill existing weeds, pre-emergent herbicide can be spread right after you mow. The reason for this difference is that pre-emergent herbicide does not need leaf contact. It enters the soil and kills weed seeds at the time of seed germination.
- You can mow right before spreading pre-emergent weed killers.
- Water your pre-emergent into the soil before mowing.
- Mowing if your pre-emergent hasn’t been watered in can throw granular weed killers out of your yard, rendering them useless.
However, if you’ve spread a pre-emergent herbicide, wait 3–7 days before you mow. During this time, make sure to water pre-emergent into the soil. Otherwise, mowing could throw the pre-emergent off your yard, ruining the application and forcing you to redo the job.
Should You Mow Before Applying 2,4-D Weed Killer?
If you’re planning on spraying a 2,4-D-based weed killer, do not mow the lawn for at least 5 days before application. 2,4-D is a post-emergent weed killer that must make contact with the leaf blade of the weed in order to work. You want unmowed, leafy weeds in your lawn when you spray 2,4-D.
Should You Spray Roundup Before or After Mowing?
As with other post-emergent herbicides, do not mow your lawn for at least 5 days before you spray Roundup. Not only does Roundup enter through the leaves, but it also needs plenty of time to infiltrate the plant after you spray. Wait 2 days after spraying Roundup or any other liquid herbicide before you mow.
Should You Mow Weeds Before Spraying Weed Killer?
When spraying your lawn for weeds, it’s important to follow these quick rules:
- Post-Emergent Herbicide: If the weed spray is meant to kill existing weeds, don’t mow your lawn for at least 5 days before spraying. Then, wait 2 days after spraying before you mow.
- Pre-Emergent Herbicide: If the herbicide is meant to stop weed seeds from sprouting, you can apply it right after mowing. However, wait until the herbicide has been watered into the soil before mowing again.
These two simple rules will help promote a healthy lawn, kill weeds, and prevent you from performing repeat weed killer applications.