Can You Spray Weed Killer On Wet Grass (Spraying Weeds Before & After Rain)

Herbicide spraying is the most popular approach to get rid of bothersome weeds in your yard.

However, as simple as it may appear, this can be a really difficult undertaking. Not only do you need the correct herbicide for the job, but you must also ensure that the time is perfect, or your efforts will be futile.

So, if heavy weather is on the way, do you spray before or after the rain? If this is the case, how long should you wait after rain to apply a herbicide? Can you spray your grass with herbicide while it is still wet?

While spraying weeds, make sure to provide enough time for the herbicide to take effect before any rainfalls. It is recommended that you spray your lawn roughly 30 minutes to an hour before rainfall is expected, if not earlier, depending on the brand you choose, to efficiently eliminate weeds.

Wait for the leaves to dry out after raining before spraying, or the herbicide may just drip right off the leaves, rendering all your hard effort pointless.

Regardless of the weather conditions, you should still check the day’s forecast before treating weeds, including the projected temperature, wind, and rain. Herbicides operate best when the leaves are dry, so spraying right before or after a rainstorm may be a waste of time and product.

Even the most seasoned gardener can be caught off guard if they forget to read the weed spray label because each product works uniquely.

It is best to be careful when spraying herbicides rather than rushing through the process, as these are potent chemicals that might pose a safety risk if overused.

If you’re still not sure what to do, read this article to find out when is the optimum time to spray weeds.

Can Rainfall Affect Weed Killers?

Yes, rain has an effect on herbicide efficacy because it washes the weed killer away from the areas that need to be treated. This is why it is not recommended to spray weeds while it is raining or shortly before it is about to rain. 

Herbicides must be soaked into the leaves in order to kill the undesirable plants. Some weed killer brands require a dry, rain-free time of up to 6 or 8 hours for the solution to sink in, and this information should be included on the bottle.

Other, stronger types, such as Roundup, just require 30 minutes on the leaves to be effective, and rain after that time will not prevent the chemical from working properly.

It’s also not a good idea to spray right after it rains. For the product to start working, you must wait for the leaves to dry prior to spraying.

Because the weeds are still moist and the weed killer is rinsed away, spraying shortly after rain is identical to spraying before the rain. Raindrops can also dilute the herbicide, making it less effective.

If you opt to spray herbicide 30 minutes or more before the rain, you should also consider the wind direction.

Spraying weeds should be avoided if the wind has picked up ahead of a storm or if the weather is especially breezy. Wind can cause the herbicide to disperse and harm plants that you do not intend to destroy.

How About Before It Rains?

If you wish to spray your pesky weeds before it rains, make sure the weed killer has enough time to dry and be absorbed by the plant.

Each weed spray will have its own set of requirements, therefore the product label is the greatest source of information.

Can You Spray Weed Killer On Wet Grass (Spraying Weeds Before & After Rain)

As previously said, spraying when it is raining or just a few minutes before is never a smart idea. It will simply reduce the herbicide’s effectiveness, assuming any product is absorbed at all and may fail to kill the weeds.

If you’re short on time and can see clues that it’s about to rain, use a rapid-acting weed killer like Roundup. Roundup’s potent herbicidal solution will soak into the leaves in just 30 minutes, however, even the manufacturers recommend waiting up to 3 hours.

And, because the weather is often unpredictable, it may rain sooner than predicted – so always be prepared.

How About After It Has Rained?

Treating weeds after rainfall can also be effective, as long as the leaves are allowed to dry. Make sure there is no more rain on the way — getting in a short spritz between showers isn’t a good idea in this scenario. 

Herbicides work much better when the leaves are dry before spraying; otherwise, the chemicals will easily run off the leaf and not be absorbed by the plants.

Basically, you may not want to spray weeds when they’re wet — whether from rain, irrigation, or dew. Waiting for the leaves to dry can take hours, and it might take even longer when the weather is cold.

That isn’t always convenient, but it does mean you won’t be spending time or money on worthless chemicals.

However, only spray weed killer after the leaves have dried, and if it rains unexpectedly after you apply your herbicide, you may need to reapply the treatment a couple of times until you get your desired results.


The weather is the most important aspect in determining when is the optimum time to spray weeds, thus this will vary from season to season. Most herbicides operate best when applied during several days of dry weather, but not over extended periods of dry weather.

Heat stress will impair the weed’s ability to absorb the herbicide if it is excessively hot or dry. The same is true for winds: if it’s too windy, the spray will fly away from the target plants and impact the rest of your garden.

If you have a next-door neighbor, you should consider contacting them and discussing your weed-spraying plans. This is to prevent causing them or their property any discomfort.

The same thing should happen in your own home, warning everyone so that pets, children, or other potted plants are not in the area during or after herbicide application.