How Long Does Roundup Take To Work

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Glyphosate [N-(phosphonomethyl) glycine] is the main ingredient in Roundup and similar herbicide products. 

Generally speaking, when you apply a product containing glyphosate, you can expect to see gradual yellowing and wilting of the offending plants’ leaves over the next few days, but in some cases, it may take as long as three weeks. 


Information found on Roundup’s website indicates that most of their products designed for use on weeds and unwanted grasses will show some results within a few hours. 

However, those designed against more stubborn plants (e.g., tough perennial weeds) may take as long as 12 hours to start working. 

Be sure to carefully read the labels of any glyphosate-containing product you are considering. For best results and safety, always follow directions closely.

Roundup & Glyphosate Q&A

1. How long has glyphosate been in use? 

The chemical was developed in the 1970s and has been widely used worldwide since 1974. In fact, it is the most frequently used herbicide across the globe. 

2. What does glyphosate kill? 

This chemical is a nonselective, systemic herbicide that will kill any green, living thing and present hazards to wildlife, pets, and people. 

3. How does glyphosate kill plants? 

When sprayed on a plant’s foliage, the chemical soaks in and enters its circulatory system to travel to the crown and roots. Once there, glyphosate pools at the plants’ base and blocks the supply of food to the plant. 

This causes the plant to shrivel within a few hours. However, complete plant death may not occur for several days or weeks. Therefore, in particularly resilient plants, complete eradication may take up to three weeks. 

4. How does glyphosate affect people, pets, and wildlife? 

Contact with glyphosate may cause immediate skin and eye irritation. In addition, ingesting or inhaling the spray will quickly irritate the throat and esophagus. This may be followed by difficulty swallowing, gastric distress, and gastrointestinal hemorrhage. 

The long-term effects of repeated exposure to this chemical have not yet been determined; however, lab animals and earthworms exposed to glyphosate in large concentrations over two years exhibit stunted growth and increase cancer rates. A link to cancer in humans has not been established.

5. Does weather impact the effectiveness of glyphosate? 

Heat speeds and supports the efficacy of the chemical, so it’s best to apply it when temperatures are greater than 60° degrees Fahrenheit. 

Rainfall will dilute the product and may potentially wash it into waterways, so avoid using glyphosate-containing products when rain is predicted within two days. 

Wind will carry the chemical to unintended destinations, so apply it carefully only to targeted plants and on still days. 

6. Why should you avoid getting glyphosate into the water system? 

This chemical, and the surfactants with which it is typically mixed, remain viable in water indefinitely. 

Its presence in waterways presents hazards to all manner of aquatic life, including but not limited to the following: 

  • Oysters and Clams
  • Aquatic plants
  • Amphibians
  • Crustaceans
  • Fish

Of course, any chemical that makes its way into waterways will also make its way into the aquatic life that eventually ends up on peoples’ plates.

Contaminated water also negatively impacts birds, wildlife, and livestock that drink the water. 

7. How long does glyphosate stay in the soil? 

The amount of time spilled or over-sprayed glyphosate remains in the soil varies depending upon the climate and the weather. 

Generally speaking, half of the herbicide will degrade in about 200 days. Its average half-life is approximately 50 days. 

8. Are there any alternatives to glyphosate?

For small applications, household white vinegar mixed with a few drops of dish soap as a surfactant can be an effective alternative to glyphosate. 

While this mixture is not as potent as glyphosate and may take repeated applications to eradicate unwanted plants completely, it does not pose threats to the environment, wildlife, pets, or people.

In some settings (e.g., concrete and brick surfaces), using boiling water or steaming can effectively eliminate unwanted plant growth. 

Combined with traditional gardening practices, such as old-fashioned weeding, these natural alternatives can effectively eradicate weeds and prevent their return when used consistently.

9. How can you use glyphosate safely?

Always read and follow packaging instructions carefully. Remember that the label is the law when using pesticides and herbicides. 

Wear protective gear when using Roundup and other products containing glyphosate. Protect your eyes, nose, mouth, and skin with goggles, a mask, long sleeves, pant legs, gloves, and closed-toed shoes or boots. 

If you get any product in your eyes or mouth or on your skin, flush the area with generous amounts of water and seek medical attention. 

10. When should you use Roundup and other glyphosate-containing herbicides? 

For huge stands of weeds, young trash trees, and very stubborn perennial weeds, careful, responsible use of these products may be the only way you can initially get results. 

Natural alternatives are safer for the environment; however, they only impact the green part of the plant. Stubborn weeds will continue to grow back from the roots.

Try a green alternative and find it is unsuccessful, focused, or targeted. Responsible use of chemical herbicides may be the only way you can get the problem under control. This doesn’t mean that glyphosate products are your only solution, though. 

A wise, orchestrated strategy of limited use of chemicals and more general use of natural alternatives allows you to eliminate unwanted plants while limiting damage to beneficial flora, fauna, and the environment. 

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