How Long To Wait To Water After Applying Weed Killer

Having a healthy lawn is the benefit of attentive care, but with good growing conditions comes the potential for unwanted plants popping up here and there.

When applying herbicide to take care of your lawn’s weeds, it needs to be coordinated with other annual lawn care activities, as well as the weather. Too wet of an environment from rain or watering will prevent weed killers from doing their job, but some herbicides prefer a moist soil environment.

Since there are several different kinds of herbicides, how soon you can water the grass after treatment will differ. The product instructions will be your best guide for the specific product you choose.

Water and Weed Killer

Herbicides target weeds at different times of the plant’s life and in different ways. Some require more time than others to dry, and some do well with moisture. However, for all kinds of herbicides, too much water right before or after application will dilute the weed killer, washing it away before it can have any effect.

Pre-Emergent Herbicide

Weed killers that focus on destroying roots before weeds can grow are called pre-emergent. These target the roots of specific types of plants that will leave your own grass’ roots unharmed. These are usually applied at the beginning of the growing seasons in spring and fall.

Post-Emergent Herbicide

Post-emergent herbicides are treatments that are applied on the weed’s leaves and stems after they show up. This way, the young plant’s tissues absorb the chemicals that wilt the leaves and stems. Unable to perform photosynthesis, the plant’s root system dies off as well.

Granular Weed Killer

Granular weed killers are small pellets of herbicide that are spread around the ground. They’re often included with weed and feed products that provide both herbicide and fertilizer. This mixed product can be challenging to apply since water will be needed for the fertilizer to soak into the soil, but too much water will wash away both the herbicide and the added nutrients.

For pre- and post-emergent granular herbicides that come with fertilizers, spreading the product on moist soil but dry leaves is a good way to balance the different kinds of products at application. Granular herbicides are a good choice for full-lawn coverage. 

Liquid Weed Killer

Liquid Weed Killer

Liquid herbicides are formulas meant for fast absorption by undesired weeds’ roots, stems, and leaves. Spraying weed killer is suitable for targeted, spot-treating your lawn but is also used for yard-wide application.

How Long Does Weed Killer Take To Dry?

Fast-acting liquid herbicides can take effect within hours after application, but it’s usually recommended to let the treatment dry a full day or two before watering your lawn next. Granular weed killer usually needs a long period of dryness, ten to fourteen days, to be sure the soil absorbs the herbicide and the roots of the plants.

Rain And Lawn Treatments

If it’s going to rain the day you go to apply the weed killer, you should avoid putting down herbicides until after the rain passes and the leaves dry off. Some herbicides need up to two weeks of dry weather for best effects, so taking a look at the weather forecast can help you avoid having your weed killer treatments diluted or washed away.

What Is The Best Time Of Day To Apply Fast-Acting Herbicide?

Since most liquid herbicides will dry within a day, it’s best to apply these in mid-morning, after any dew has dried, but before the sun’s heat will threaten to evaporate the liquid before it’s absorbed.

Which Kind Of Weed Killer Is Right For My Lawn?

When choosing an herbicide, make sure your choice of product is safe for grass. Some weed killers are made for gardens that don’t want grass present, and other weed killers will eliminate any and all vegetation it touches. Some weeds take specially targeted formulas, like crabgrass and other grassy weeds that aren’t effective against grass-safe herbicide formulas.

Most grass-safe weed killers will include a list of plants they target and which they are safe on. For example, Scotts Turf Builder Weed And Feed will focus on broadleaf weeds like dandelions and clover. At the same time, it’s safe for most types of grass, including zoysia, Kentucky bluegrass, fescue, and several others.

This product’s instructions say to apply to a damp lawn and to wait a day before watering again.

Another example is 24D, an herbicide ingredient in many liquid weed killers as a popular turf-safe choice for weed control. After application, it’s water safe after a few hours, but if you follow the rule of thumb, giving a full day or two to be absorbed will produce the most thorough results.

Coordinating Lawn Care

Lawn Care

A lot of effort goes into keeping up green lawns: applying fertilizer, pesticides, and herbicides can all be coordinated with other lawn care responsibilities like planting and mowing to have their biggest impacts at the right time of the season, but it will take a little planning to make sure they don’t interfere with each other.

Preparing your lawn to be treated with weed killer may begin a week before you apply it or longer if you’re waiting for the right weather forecast.

For pre-emergent treatments, mowing the yard and raking up thatch will help expose the soil to accept the herbicide. Wait a week after mowing for the grass blades to heal, so that weed killer doesn’t get in the open cuts of the grass blades.

Even though the formulas are usually safe for grass, the open cuts on the blades are sensitive and may affect the products. Giving the most time for herbicides to dry and take effect, waiting another two weeks after application to mow again will give the product time to work into the weeds and clear up.


Author: Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.