Should I Cut Weeds Before Spraying Roundup? Is It Good

Pulling weeds by hand can be very tough and time-consuming when you have a lot of them on your lawn. It would be much easier if you let a concentrated weed killer do the job for you with little time and no effort at all. 

But before applying these herbicides, some people mow their lawn thinking that it will help the herbicide work faster. But trimming the lawn before applying herbicide can be bad. 

Herbicides like Roundup need time and surface area of the plant to work their way from the leaves to the root of the plant to properly kill the whole plant. Mowing will reduce the surface area of the plant and the chemical herbicide won’t have enough surface to stick to and get absorbed. So don’t mow the weeds before spraying herbicide.

Let’s look in detail at how herbicides work on weeds and how to spray them properly for good results. 

Should I Cut Weeds Before Spraying Roundup? Is It Good

How does Roundup Or Other Weed Killer Spray Work?

Roundup or other post-emergent herbicides are glyphosate-based herbicides which means that they can’t directly go into the soil and kill the roots of the plant. Glyphosate needs to get absorbed by the leaves of the plant and then carried into the roots to kill the whole plant.

Another factor of glyphosate-based herbicide is that it can’t differentiate between weeds and other plants which means it will kill all the plants that come into its contact. That’s why you need to take precautions and spray the herbicide only on the weeds and not on other plants.

Can You Mow Before Spraying Weed Killer?

The chemical herbicide needs leaves on the plant to absorb it and take it to the roots of the plant so that it can work. So if you mow the weeds before spraying the herbicide, you will just remove all the surface area of the herbicide to work and the herbicide won’t have much area to stick to and get absorbed and will runoff into the ground, which isn’t effective. So you shouldn’t mow weeds before spraying weed killer. 

If you have mowed the lawn and now want to put in the herbicide, wait for at least 5 days to let the weeds grow new leaves which will then help the herbicide to get absorbed and get into the roots. 

How Soon After Spraying Weed Killer Can I Mow Weeds?

After you apply the herbicide to the weeds, the herbicide needs to get absorbed by the leaves of the plant and bring it to the roots of the plant. If it doesn’t get to the roots of the plant, the herbicide won’t kill it fully and the weed can grow back from the roots. 

If you mow the weeds immediately after spraying the herbicide, the leaves won’t be able to absorb the herbicide and won’t have any effect. So give the weeds at least a day to absorb the herbicide and have an effect on the roots. 

For the best result of herbicide on the weeds, I recommend you to at least wait for 5 days which will ensure the herbicide is gotten to the roots and the plant will get fully burned by the herbicide.

How To Spray Weed Killer On Your Lawn? 

There are 2 ways you can spray the herbicide, Spot spray, and Blanket spray. The use of these two methods depends on how much weed you have in your yard. 

If you have a small number of weeds here and there then use spot spraying in your yard but if you have a lot of weeds all over the lawn then blanket spraying would be the better option. Let’s talk about each spraying method in detail:

Spot Spray – If you have a few weeds in your lawn here and there in your lawn then spot spraying it with an herbicide would be effective and efficient and will take less time and effort. You can just fill up a spray bottle with the herbicide mix and spot spray directly to the weeds. Spray the weeds 2-3 times a week to get good results. 

Just try to moisten the weeds and not overly spray them as the runoff herbicide is not useful as it doesn’t have any effect on the soil. You can also add a little bit of soap mix or baby shampoo so the solution sticks to the weeds effectively and has more effect. 

Blanket Spray – Blanket spraying (spraying the whole yard) with herbicide in the yard is used when it is full of weeds. This method will be more effective and take less time than spot spraying a lot of weeds. 

For blanket spraying, you need a large amount of herbicide mix and for that, you can use a backpack sprayer or a sprayer that can hold a larger amount of solution. Spray the whole yard with the herbicide and just moist the plants with it and not overspray as you don’t want the herbicide to runoff.

Note – If you are using RoundUp or other non-selective herbicide. Keep in mind that these chemicals don’t differentiate between weeds and other plants and will kill any plant which comes in contact and absorbs it. So spray only to the weeds when spot spraying and only use blanket spraying when you want all the plants to be dead. 

If you want to keep the grass safe on your lawn then select a herbicide that clearly mentions that it won’t kill the grass which is growing on your lawn, like Ortho Weed B Gon Weed killer.

What Is The Best Time Of Day To Spray Herbicide On Weeds?

The best time to spray herbicides on weeds is in the morning or in the evening. There is a misconception that herbicides need hot weather to burn the plant but on the other side, herbicides work best in cool temperatures. 

Also, the plant needs to absorb these herbicides and bring them to the roots to make the herbicide work, but plant growth slows in the afternoon and after sunset and speeds up again when the sun rises. So it’s best to apply fertilizer when the plant is growing at its best.

Don’t apply herbicide really early in the morning as the herbicide can run off due to heavy dew on top of the plant, so it’s best to wait for the dew to evaporate after the sunrise and then apply the herbicide.

When To Water The Yard After Spraying Weed Killer?

You need to wait at least 2 to 3 days before watering the yard as the herbicide needs to get absorbed by the weeds and get to the roots of the plant and be effective. If you water the yard early, the herbicide will runoff from the weeds and won’t get absorbed which will ruin all your efforts. 

If your lawn is healthy and in good shape, try to hold on to the water for at least 5 days, which will make the herbicide application more effective and kill all the weeds in the yard. 

Should I Water The Yard Before Spraying Weed Killer

No, you shouldn’t water the lawn before spraying weed killer as it will make the leaves wet and the herbicide will runoff from the leaves and not stick to it. Also, the leaves will get the water content for the day and they will stop absorbing and not absorb the herbicide which is crucial for the herbicide to work. 

If your lawn is extremely dry then water it fully and then wait for a day or two before spraying weed killer on the plants. This will make the application effective and give you better results. 


So if you want to spray weed killer in your yard, you shouldn’t trim the weeds as it will reduce the leaf count as well as the surface area for the herbicide to stick and get absorbed by the weeds. If you have trimmed the yard already then wait for at least 5 days for the new leaves to grow, which will help the herbicide get absorbed and get to the roots of the weeds.