Glyphosate Weed Killer : Friend or Foe?


Glyphosate Concentrate: Are there Hidden Dangers in Your Weed Killer?

Glyphosate in concentrated or ready to use form is the worlds most popular, arguably strongest & currently the most controversial weed killer.

Glyphosate is a herbicide that is used to kill weeds, grasses, and other unwanted vegetation. It is used in both agricultural and non-agricultural settings to control almost all kinds of weeds.

It was first discovered in the 1950's by Henry Martin who was looking for pharmaceutical properties and new drug discoveries, he realised it was of no use to himself and quickly discounted it, the discovery lay dormant for more than a decade, until...

Monsanto came calling and discovered it's weed killing properties. Glyphosate was popularised in the 1970s by Monsanto under the brand name of Roundup.

It was once described as a "once in a century discovery" this synthetic herbicide has made huge contributions to world food security due to the nature of GMO crops.

Can you still buy Glyphosate in the UK?

Yes! Glyphosate is the most popular weed killer in the UK.

It is sold under various brand names (Roundup, Gallup, Resolva, Doff - even Tesco!) almost every effective weed killer sold in the UK contains Glyphosate - check the label of your product and it will tell you the concentration of Glyphosate usually something like:  contains 90g/l Glyphosate.

Is it safe to use?

Yes! Glyphosate when used according the manufacturers instructions is perfectly safe to use around your garden or farm. Great care should always be used when using any kind of herbicide, even so called homemade weed killers can be toxic.

Why is it so controversial?

There have been several lawsuits aimed at Monsanto the creator of RoundUp & Glyphosate (which they lost). The plaintiffs developed non-Hodgkin lymphoma and the IARC classified Glyphosate as a possible carcinogen for humans (WHO did it with red meat too).

There is no strawman argument here, persistent and long term exposure to any herbicide is likely to be risky - the problem is the way companies market them and the way companies/people use them.

I don't want to downplay the risks associated with Glyphosate, long term & frequent exposure may result in harmful consequences for humans but irregular use around your garden to kill a few weeds? As long as the proper care is taken you and your pets will be fine.

Another factor that makes Roundup and Glyphosate so controversial is that it has made it into our food supplies and bodies. It is used widely in GMO crops: Seeds are genetically modified to be immune to it's plant killing properties and the Glyphosate is sprayed indiscriminately.

Cereals such as oats, soy, wheat and barley are often sprayed with Glyphosate just before harvesting as it dries them out evenly & quickly allowing for an earlier harvest - farmers can only harvest certain crops when the moisture level reaches a certain percentage.

Glyphosate has been found in beer, wine, breakfast cereals & even urine! It is everywhere! I must stress that the amounts found are miniscule so there is no need to worry but Governments & scientists have yet to look into the affects of long term exposure in small amounts.

Is it harmful to humans?

Pure Glyphosate has a low toxicity but different manufacturers use "surfactants" and other "secret" ingredients to up the effectiveness and allow the Glyphosate to penetrate plants more quickly: these additional ingredients may be more toxic than Glyphosate itself.

Common side affects of exposure to Glyphosate include:

  • Eye irritation if mist or product comes into contact with eyes.
  • Skin irritation if the product comes into contact with the skin.
  • Nose and throat irritation from breathing in the sprayed mist.

There have been fatalities reported due to intentional ingestion of Glyphosate based products. In cases of ingestion (swallowing) contact your local poison centre immediately and take the label or container of the product with you.

It is important that you store Glyphosate products correctly: Out of reach of children, in a cool, dry dark place and please read the label, strap on some gloves and protective eyewear.

Is Glyphosate a pet friendly weed killer?

Yes! Glyphosate is safe to use if you have pets. You should never use it in aquatic environments as it persists in water and is toxic to aquatic creatures. 

If using Glyphosate around household pets you should exclude them from the treated area until the solution has dried; this prevents the pets from stepping in it and spreading it elsewhere or accidentally ingesting it for example: by eating treated weeds.

What is stronger Roundup or Glyphosate?

RoundUp & Glyphosate are one and the same. RoundUp was created by Monsanto and bought out by Bayer Chemicals, the active ingredient that kills weeds in RoundUp is Glyphosate.

RoundUp popularised Glyphosate and it quickly overcame all other weed killers. The patent for Glyphosate expired in the year 2000 and it is now manufactured and sold under a whole lot of different brand names such as Doff, Resolva, Gallup, Rosate and so much more.

What concentration should I use?

Typically the higher the concentration the more effective and quickly the weed killer gets to work. Some higher concentrates are strictly for professional use in the UK.

Cheaper Glyphosate products such as Doff, Resolva & Pet Shield will contain upto 90g/l of Glyphosate. More expensive brands such as Gallup & Rosate contain upto 360g/l which is 4 times more than the cheaper brands - in weed killer as in life: you get what you pay for!

What happens if I use to much?

Every manufacturer of weed killers must include specific instructions. If you have a concentrated product, there will be exact measurement guidelines to ensure you use the product safely, correctly & it does the job it's supposed to - you have to read the label!

But what happens if you accidentally use more than the manufacturers guidelines? Will it kill your garden? Does it make the whole area a toxic waste dump? 

The first thing you should do before using Glyphosate to kill weeds is READ THE LABEL!

If you use to much Glyphosate you may:

  • Allow Glyphosate to seep into nearby waterways, this can be toxic to aquatic invertebrates and as Glyphosate persists in water it may contaminate local water sources.
  • If over used for longer periods of time you may induce Glyphosate resistant weeds, these weeds "evolve" to be resistant to Glyphosate making them harder to kill.
  • Whilst not harmful to humans when used as directed Glyphosate used in larger quantities can be toxic to human and animal life. Please READ THE LABEL!
  • Using too much can also contaminate your applicator (sprayer, watering can etc). If you use it next time on ornamental plants it will kill them as it's active in low doses.

How long does it stay in the soil?

One of the main reasons Glyphosate is so popular (besides it's excellent weed killing properties) is that it tightly binds to soil and is degraded by the bacteria in soil.

In practice this means that once your weeds are gone you can safely replant in the same area with no ill affects. For example: If your lawn is covered in weeds and you want to kill your grass & start over - you can do it, the new seeds will grow and the area isn't turned into toxic dump.

Glyphosate is systemic meaning it can only kill the weeds it is applied to. Once applied it is transplanted throughout the whole plant killing it from the inside out. However if applied directly to the soil surrounding weeds it will have no affect.

How much do I need for X litres of water?

Almost every Glyphosate concentrate product has different requirements for dilution. Not all weed killers are the same, typically specific instructions for dilution will be included on the label.

Lost or damaged the label? Text to small to read? We have included the dilution rate of some of the most popular Glyphosate weedkillers below:

Product Name


Dilution Rate

Gallup XL


24ml per Litre

Gallup Home & Garden


24ml per Litre

Roundup Optima


20ml per Litre

Doff Advanced


80ml per Litre

RoundUp Tree Stump


10ml per Litre

Weedol Ultra Tough


25ml per Litre

Resolva 2 Action 


15ml per Litre

Rootblast Concentrate


15ml Per Litre

Weedol Pathclear


18ml Per Litre

Resolva Xtra Tough


16ml Per Litre

Will Glyphosate kill my weeds permanently?

Yes. Pretty much any weed you apply Glyphosate to will completely die, never to return. There are some exceptions: Large woody or viney weeds such as Brambles, Ivy & Marestail may require repeated treatments (depending on how long they have been established).

But you used Glyphosate and you still have weeds?! How can that be! Glyphosate only kills weeds you apply it to, it will not stop new weeds from growing. If you don't resolve the underlying problems, new weeds will grow!

If you wanted to prevent weeds for a while, use a residual weeds killer - these will prevent germination of new weeds but again, they aren't permanent.

What kind of weeds won't it kill?

Some larger invasive species such as Brambles & Ivy may require multiple treatments but it will kill them if you keep at it. Japanese knotweed can be killed with Glyphosate but if it has been established for a while, it may not be possible.

Glyphosate doesn't kill moss or lichens, however there are many dedicated products for this.

Glyphosate won't kill mature trees but it can prevent tree stumps from regrowing.

If the world ever phases out Glyphosate it will be very difficult to replace. One of the major benefits of Glyphosate is that it kills a broad spectrum of weeds effectively.

The best way to apply Glyphosate?

Before applying any weed killer you should ALWAYS READ THE LABEL.

The best way to apply Glyphosate is to use a sprayer.

If you have just a few weeds: A handheld sprayer works, larger areas would benefit from a 5 litre pressure sprayer or larger capacity knapsack sprayer.

Sprayers allow you to quickly & accurately apply the weed killer without the risk of overspill.

We do not recommend you use a watering can:

Watering cans: Even with a fine rose are inefficient, not only do you waste product by pouring it into the soil you also run the risk of killing ornamental plants with the runoff from excess

Do not use a watering can to apply weed killer!

Have a designated sprayer for weed killers. Glyphosate is active even in small doses. Do not use the same sprayer for watering, cleaning or any other activity - it's not worth the risk.

How long does it take to kill weeds?

Glyphosate is not the fastest weed killer but that works to it's advantage.

Paraquat the weed killer that was widely used before Glyphosate killed weeds much quicker but this often resulted in the weeds dying before the chemical had a chance to penetrate the root system allowing them to regrow.

Glyphosate typically kills weeds within 10-30 days, it starts off slow. You'll notice the leaves start to yellow, you may even see your weeds grow a little but this is common. Within 2 weeks all the leaves should start to change colour and eventually the weeds will die.

There are some exceptions to this. Large deep rooted perennials such as Brambles, Ivy, Dock, Thistles may take slightly longer or require a repeat treatment depending on how long they have been established. Please refer to your product label for more information.

Closing thoughts

Glyphosate has hit the headlines in recent years due to lawsuits and of course it's use in GMO crops has long been vilified. The fact that it was patented by Monsanto who many think are the devil reincarnate, Glyphosate hasn't had an easy time of it.

At times of controversy many well intentioned people and companies do things that aren't backed by the science. France has banned use of Glyphosate and B&Q pulled it from their shelves but almost every government around the globe as well as a whole host of scientists still say it's safe.

Long term exposure to Glyphosate may have unintended side affects, there is some evidence that this is true but short term use by the average gardener is unlikely to be harmful.

It is commendable that you want to use less weed killer - we all should but for the time being Glyphosate is by the most effective tool we have available to combat weeds at home.

As they say: Be careful what you wish for! Who's to say the next weed killer that comes along will be any better? New herbicides often fall out of fashion after years of use due to unforeseen side affects. Glyphosate has been used widely for over 50 years & the controversy continues to grow.

Governments should crack down on Glyphosate use as a desiccant and lower the levels found in our food stuffs (animal food too) - this is easier said than done but it should be done!

Whatever happens, we know that Glyphosate will be hard to replace, if that time ever comes.


Does Glyphosate kill Japanese Knotweed?

Yes, glyphosate can be used to kill Japanese knotweed. Glyphosate is a broad-spectrum, non-selective herbicide that kills or slows the growth of many kinds of weeds and plants, including Japanese knotweed. It is typically applied as a foliar spray, meaning it is sprayed directly onto the leaves of the plant.

The main benefit of using glyphosate to kill Japanese knotweed is that it is an effective and relatively inexpensive method of controlling the weed. It is also relatively easy to use and can quickly reduce the size of the plant.

However, there are some disadvantages to using glyphosate. It can be difficult to completely eradicate Japanese knotweed using glyphosate, as even a small amount of the weed can quickly spread.

You may require a higher dosage of Glyphosate which may only be used by professionals in the UK: If in doubt, contact a specialist.

Does Glyphosate kill Marestail or Horsetail?

Yes, glyphosate is effective at killing marestail (horsetail). Glyphosate is a broad-spectrum systemic herbicide that is used to control a wide variety of weeds, including marestail.

It works by inhibiting the production of certain enzymes needed for plant growth.

Marestail has a waxy coating which can make it difficult for the Glyphosate to penetrate. It is advisable to rake over the Horsetail before applying.

Please note, Horsetail / Marestail may require several treatments over multiple seasons - this isn't a small job that can be done in one go.

What is the best alternative to Glyphosate?

The best alternative to glyphosate is to use other weed control methods such as mechanical, cultural and biological. Mechanical weed control includes hand-weeding, hoeing, tilling, and mowing. Cultural weed control includes crop rotation, mulching, cover crops, and interplanting. Biological weed control includes using beneficial insects and nematodes to control weeds.

Benefits of using these alternatives include:

Reduced environmental impact - Mechanical, cultural, and biological methods do not rely on chemical pesticides, so they do not pose a risk to the environment.

Cost savings - Mechanical, cultural, and biological methods are generally cheaper than chemical pesticides.

Longer-lasting weed control - Mechanical, cultural, and biological weed control methods can provide long-term weed control, whereas chemical pesticides may need to be applied multiple times.

Disadvantages of using these alternatives include:

Time-consuming - Mechanical, cultural, and biological methods can be more time-consuming than using chemical pesticides.

Limited effectiveness - Mechanical, cultural, and biological methods may not be as effective as chemical pesticides in controlling certain weeds.

Difficult to use - Mechanical, cultural, and biological methods may be difficult to use in certain situations, such as infestations of hard-to-control weeds or the requirement of expensive equipment.

Does RoundUp kill everything or just weeds?

RoundUp will kill everything (almost). Great care is required when using RoundUp it is non-selective meaning it will kill almost any kind of plant it comes into contact with (some exceptions apply).

Do not use RoundUp on windy days as it may drift onto ornamental plants / grasses you wish to keep.

Does RoundUp kill grass?

Yes RoundUp and other Glyphosate based weed killers are very, very effective at killing all kinds of grass. It is not advisable to use RoundUp on your lawn unless you very accurately spot spray the desired weeds.

Got questions about Glyphosate concentrated weed killers? Or Glyphosate in general?

Feel free to post your questions in the comments below & we'll be happy to answer.

About the author 


Hey there, I am founder and editor in chief here at Good Grow. I guess I've always known I was going to be a gardener. I'm on a mission to share my UK based weed control & lawn care tips with you all. If you have any queries please post in the comments below.

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