How Long does it Take for Atrazine to Work

If you have a problem with weeds in your lawn, Atrazine is a very popular and widely used herbicide that you can use on your lawn to control annual weeds and weeds with broad leaves.

It’s an affordable chemical and a pre-emergent herbicide that will help to prevent weeds from competing with your grass and crops during the growing season.

However, because of the potential for Atrazine to contaminate the water and the safety hazards involved with using it, it can only be handled by a licensed applicator. 

how long does it take for Atrazine to work? It takes a long time, about 15-20 days to kill the weeds on your lawn or garden because the toxin has to first get absorbed into the roots before traveling to the leaves. It’s then able to inhibit photosynthesis and this causes the weeds to starve to death.

What is Atrazine?

Atrazine is an herbicide that is mostly used to kill weeds. It’s effective as both a pre-and post-emergent herbicide for both home and agricultural purposes to control broadleaf and annual weeds.

In pure form, it’s an odorless, white powder that you can dissolve in water. It’s used on crops like sugarcane, macadamia nuts, corn, sorghum, pineapples, and evergreen trees, and also for controlling weeds before they invade your lawn.

Its use during the spring and summer months.

Is Atrazine safe?

Atrazine is an efficient and popular herbicide yet very controversial.

Although there’s no evidence that it’s harmful to humans, it can get absorbed into your body if you breathe it in, but it doesn’t build up or stay in your body, it leaves within 24-48 hours primarily through your urine and fewer amounts in your feces.

If you come in contact with atrazine-contaminated water or soil, some small amount can pass through your skin and get into your bloodstream.

Although it’s an efficient weed killer, there’s research that shows that its chemicals leach into the water sources and with time builds up to toxic levels that can be deadly to small animals like frogs, birds, and bees.

However, Atrazine doesn’t seem to build up in living organisms like fish, clams, or algae so it doesn’t seem to affect the food chain. It’s recommended you take safety precautions because direct exposure can still be dangerous.

When spraying your lawn wear protective gear, don’t allow pets around when spraying the weeds, and keep your kids and pets away from the treated areas until it’s completely dry.

How to use Atrazine

Although Atrazine is a very effective herbicide for your lawn, it’s a very controversial chemical that you need to know how to handle safely.

  • Preparation

Atrazine is bought in a concentrated form that you can’t use in that form on your grass. You’ll need to mix the chemical with water by carefully following the instructions on the label depending on your lawn dimensions.

Don’t mix Atrazine with another weed killer because it a surfactant so you don’t need to combine it with another product for it to be effective.

  • Weather conditions

Unlike other weed killers, you’ll need to check the weather conditions for the best time to spray this chemical on your lawn.

It’s best to spray Atrazine when the temperatures are between 65-90 degrees F., but if the temperatures go over 90 degrees, it won’t be effective in that heat.

You should also use it spray it on dry ground, so if it rained 2 or 3 days after you applied it on your lawn, you’ll need to reapply it again. Overwatering your lawn can make the weed killer less effective.

  • Application

Always remember to wear protective clothing when spraying Atrazine on your lawn because direct contact with this chemical can be harmful to your health.

This herbicide will get rid of all the weeds that are growing and even the seeds that haven’t germinated yet.

Once you apply it you don’t need to water your lawn immediately, wait 7-10 days after your first application. Atrazine is best applied when your lawn is slightly damp, but not very wet.

Once you apply it, it remains effective for several months, but you’ll need to spray it twice a year to maintain its effects and keep the weeds away from your lawn all year round.

It also ensures that you get rid of any weeds that you missed in your first application. The best time to spray Atrazine is in January before the weeds recover from the winter and in November when the crops have been harvested and a lot of seed is in the air.

How does Atrazine work?

Atrazine is a chemical that inhibits the process of photosynthesis in the leaves and roots of weeds. The herbicide is absorbed into the roots before it travels to the leaves of the plants.

Although there’s some absorption that happens directly through the leaves it’s not enough to kill the weeds, it’s not enough to kill the weeds until it’s absorbed through the roots first.

You should also note that Atrazine is also absorbed by other plants, but the plants break it down before it can affect their process of photosynthesis.

Methods of herbicide application for weeds



Suited for

Foliar spray

Dilute with water and spray over the foliage until the leaves are wet but not dripping

Grasses, scrubs, and dense vines

Basal barking

Mix an oil-soluble herbicide with diesel and spray around the trunk and stem of the weeds

Undesirable trees, thin-barked woody plants, and multi-stemmed shrubs and trees

Cut and swab

Cut the weed stem close to the ground then apply the herbicide on the cut surface by spraying or brushing

Vines and multi-stemmed shrubs

Stem scraper

Use a sharp knife to scrape a thin layer of bark from the stem and apply the herbicide on the exposed underlying green tissue

Vines with aerial tubers


Keeping your lawn nice and tidy is a hard job, especially when weeds keep invading your lawn. Using the right product like Atrazine will keep the weeds under control if you follow the instructions.


How long does it take Atrazine to dry?

Atrazine weed killer takes 4 hours after application to dry.

Does Atrazine need to be watered in?

Atrazine controls both growing weeds and weeds from seeds and water or rain within 2-3 days can reduce its effect on the weeds. However, you can water after 7-10 days of treatment.

Also read

How Much Atrazine per Gallon of Water

What Weeds Does Atrazine Kill?

Simazine vs Atrazine

Will Atrazine Kill Bermuda Grass?

References and Sources

Public Health Statement for Atrazine

Atrazine -US EPA United States Environmental Protection Agency

Atrazine – National Pesticide Information

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