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How long does Roundup last in the soil?

by Jackson White

Roundup has long been used as an effective chemical against weeds in farms and on grass lawns across the globe. However, several schools of thought have argued that overuse of this chemical can be harmful to your plants and soils. Is there any truth to it?

The success of Roundup as a weed killer is attributed to its ability to penetrate the weed’s leaves and kill it from the inside. This chemical is largely constituted of glyphosate which is the active ingredient in the herbicide. Ideally, this chemical is meant to be sprayed directly onto the leaves of the weeds. However, there is no way of stopping it from getting into the soil. So, how long does it stay in the soil? Roundup could remain in the soil for anything between 2 and 200 days, BUT it is largely inactive during a significant length of this period.

Once applied, the plants rapidly absorb it and die off within a few days as the glyphosate begins to work. This chemical works by inhibiting a growth protein, a characteristic that causes the plant to wither and die off. Roundup’s active component, glyphosate, is non-specific and affects all plants, and this is why you have to take care not to spray it on the plants you intend to keep. Its universal effect is what makes it one of the most popular herbicides in the globe.

So, does glyphosate have a significant effect on your soils and other elements?

Effect of Glyphosate on soils and other elements

Effect of glyphosate
Lasts a period of a few days to several months, does not affect seeds and plants after germination, cannot be absorbed by plants through the roots, biologically bound by soil
It is soluble in water, causes no adverse effects unless the water is consumed
Does not interact with air
May have long lasting effects when ingested, it is poorly digested by mammals
Poorly digested, stays in the body for an approximate 10 days, may have long lasting effects such as systemic inflammation, diabetes, heart disease and cancer
Aquatic life and amphibians
May affect the physiology of aquatic animals, increases sensitivity in amphibians

Roundup in the soil – What happens?

When you spray weeds with Roundup, it is almost given that a good amount of the chemical will make its way into the soil. This is because the application method, usually spraying, is difficult to control, and you can hardly determine where the droplets of the chemical will fall. So, what happens to it when it falls into the soil?

Roundup is ideally made to have a direct effect on plants, and it therefore, has little effect on the soil. In the event that it gets to the soil, it is broken down over time into carbon dioxide and nitrogen. However, often times, a good percentage of it remains intact, but it gets biologically bound to the soil. This binding makes it inaccessible to plants, and it, therefore, cannot be absorbed via the plants’ roots. Additionally, it does no harm to seeds that may already be existing in the soils, and they will germinate in spite of the chemical.

Additionally, Roundup acts as a post emergent herbicide, an indication that it would have no effect on emergent weeds days after it has been in the soil. As earlier mentioned, it can take 2 to 200 days for it to clear from the soil, and this period is largely dependent on the quantity of chemical in the soil, and its strength. Additionally, highly organic soils bear the capacity to absorb, break it down and bind it than less organic soils. On top of this, factors such as temperature, humidity and light intensity also affect the rate at which Roundup in the soil is broken down.

In case this chemical gets inadvertently sprayed on good crop or grass on your lawn, proceed to wash it thoroughly with clean water. Roundup (glyphosate) is highly soluble in water and it will be washed away and not damage your good plants. In this regard, avoid spraying it on your weeds during the rainy season. It could easily get washed away by rain water and have no effect on the weeds.

So, how long should you wait to plant new seeds after applying Roundup?

The waiting time between spraying Roundup and planting new seeds is determined by the plants you intend to grow. In the case of shrubs, trees and ornamental flowers, it is perfectly safe to plant them the very next day. If you want to plant edible crops and grass species, you should wait a minimum of three days before planting.

What about Roundup Ready Crops?

The manufacturer of Roundup, Monsanto, has in the recent past developed crops that have significant resistance to Roundup. They are referred to as Roundup Ready Crops, and they remain unaffected by this weed killer. With these, you would not have to worry about spreading the herbicide on them as you spray the weeds since they cannot be killed by the chemical.

Are there alternatives to Roundup that do not last too long in the soil?

If you have your reservations about eliminating weeds with Roundup which may stay in your soils a good deal of time, you can try alternative weed killing methods that would have no effect on your soil.

For instance, home remedies such as vinegar and dish soap solution works quite well on weeds and will have no effect on your soil. Additionally, you can use methods that also benefit your soils such as solarization which kills off the weeds and converts them into manure for your lawn and other plants.

Final thoughts

Even though Roundup has been a fast and effective weed killer for years, it comes with many adverse effects to the plants and living organisms in the soil. It stays a good deal of time in the soil, and although it remains unavailable to other plants, it would be a better idea to use methods that leave the soil in its original or even better state.


Are iron-based herbicides harmful to the soil?

A good number of them have been approved for use by the EPA. Make certain that your chosen herbicide is safe for plants and soils before purchase.

Is manual weed removal effective?

Yes, it is, but be sure to uproot the whole plant right from the roots.

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