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Roundup Weedkiller Instructions

By Kimberly Richardson ; Updated September 21, 2017
Weeds are invasive, tenacious plants.
Sidewalk Dandelions image by Boris Ermant from Fotolia.com

It doesn't take long for the first days of warm weather to trigger the first wave of a weed invasion. They seem to pop up overnight, squatting between sidewalk cracks and lurking in flowerbeds. While hand-weeding is effective, applying a weedkiller with glyphosate will kill the entire plant, including roots that gloves and trowels often miss. Roundup is the most popular herbicide in the world, according to Mosanto, the company behind the glyphosate-based weedkiller. Like any weedkiller, Roundup must be used carefully, according to directions on the packaging. When used properly, killing a weed with Roundup will ensure that particular pest doesn't return to the yard.

Select the right day and time to spray. Plants must be green and growing for the glyphosate and surfactants in Roundup to be effective, with temperatures preferably above 60 degrees F. However, temperatures should not be above 85 degrees F, as the solution may vaporize at these higher temperatures and drift to nearby plants. Do not spray on windy or even breezy days. Spraying when rain is forecast is not recommended, but Roundup is waterproof after 10 minutes.

Roundup will kill tadpoles or other aquatic animals.
Dutch spring garden with a pond and art decoration, Keukenhof image by e_annen from Fotolia.com

Dress appropriately in long sleeves, gloves and full-length pants to avoid blowback or skin contact. Keep all pets from the yard, and cover any water gardens or ponds.

Always make sure the spray head is tightly screwed onto the bottle.
spray nozzle image by Bruce MacQueen from Fotolia.com

Turn the nozzle from the 'X' position, which is closed, to either spray or foam. Spray is more effective on wider areas, while the application of foam is easier to control when spraying among desirable plants.

Never allow any herbicide to remain on your skin.
washing hands image by Julia Britvich from Fotolia.com

Spray the unwanted plants or weeds, coating them until they are wet or covered with foam. Use cardboard or another stiff barrier to prevent nearby plants from overspray. If skin contact occurs, wash immediately with soap and water.

Immediately rinse any plants that were accidentally sprayed with Roundup. Roundup will be absorbed into the plant within 10 minutes; rinsing after this time frame will not save the plant from damage.

When finished, close the nozzle by returning it to the 'X' position. Store the bottle out of direct sunlight and protect it from freezing. Roundup has a shelf life of four years, so unused solution can be used over multiple seasons. Change out of any sprayed clothing and wash thoroughly; Angela O'Callagan, PhD., of the University of Nevada Extension recommends showering, since many herbicides can remain active for long periods of time. Empty containers can be recycled.


Things You Will Need

  • Roundup weed killer
  • Gloves
  • Long pants
  • Long-sleeved shirt


  • Roundup's advertising mentions weeds dying within hours under ideal conditions, but a weed may take a week or more to die, especially in cooler temperatures. Many tough weeds will require a second spraying.
  • Roundup is a non-selective herbicide; do not use it to kill weeds in lawns as it will also kill the surrounding grass.


  • In 2009, the EPA announced it will re-evaluate the possible side-effects of pesticides and herbicides, including Roundup's glyphosate. Bill Chameides, dean at Duke University's Nicholas School of the Environment, says that human cell damage by Roundup is greater than the damage caused by glyphosate alone. He also points out studies linking Roundup to various health issues. Take every precaution when using Roundup.
  • Glyphosate is also found in other brands of weed killer. Read labels carefully.

About the Author


Kimberly Richardson has been writing since 1995. She has written successful grants for local schools as well as articles for various websites, specializing in garden-related topics. Richardson holds a Bachelor of Arts in English and is enrolled in her local Master Gardener program.