Glyphosate (Roundup) weed killer – should you use it?

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At two recent allotment committee meetings the subject of ‘weed killer use’ has come up for discussion; most of us are firmly against it but we know others prefer to use it like water on their plots to keep weeds down. I sit firmly on the side of those who prefer to be Glyphosate free – but why have I made that decision?

What is Glyphosate?
Glyphosate is a herbicide (weed killer) invented by a company called Monsanto. It inhibits an enzyme that is essential to plant growth; so, once sprayed onto a plant (along with some other chemicals), it’s absorbed through the leaves and spreads throughout the plant, shutting down the plant’s ability to continue growing and consequently it dies. Monsanto has invented several GM crops which are ‘Glyphosate-resistant’; enabling farmers to spray them safe in the knowledge that only the weeds around them will die. It’s meant to boost crop yield. Aside from the fact that Glyphosate regularly turns up in our bread [1], since 1996 Glyphosate has also found its way onto the shelves of our garden centres as ‘Roundup’.

Laziness at the allotment?
As far as I can tell, the main attraction of using a weed killer such as Glyphosate based Roundup is minimal effort (or as I call it laziness). When faced with an overgrown plot (which I accept can be very daunting) it’s obviously much easier to spray the whole site in an hour and wait a few weeks at home with the television than spend 6 months to a year laboriously double-digging to remove weeds by hand. If you’re suffering with a severe illness or disability you may have a legitimate excuse but otherwise I find that it’s the strenuous digging that I enjoy and it’s half the reason I have an allotment – it keeps me physically and mentally fit. You also really get to know your plot when you dig it by hand; you find areas of rich soil that you can relocate into a raised bed, you find coins, toads, rusty tent pegs and old matchbox cars and then there’s just the sheer satisfaction of looking back at what you’ve achieved with just a fork and spade!

Yes… but is Glyphosate safe to use on my allotment?
To all intents and purposes I don’t recommend anybody use Glyphosate on their allotment because the safety information being given to us (the public) is confusing and is not 100% conclusive either way:

  1. In March 2015 the International Agency for Research on Cancer (IARC) (an arm of the World Health Organisation) declared Glyphosate ‘probably carcinogenic to humans‘ [2].
    There is limited evidence in humans for the carcinogenicity of glyphosate. A positive association has been observed for non-Hodgkin lymphoma. There is sufficient evidence in experimental animals for the carcinogenicity of glyphosate.’ For reference the IARC classifies compounds on a scale of decreasing certainty:

    • group 1 is for agents that are definitely carcinogenic to humans;
    • 2A, probably carcinogenic to humans; (GLYPHOSATE SCORED 2A)
    • 2B, possibly carcinogenic to humans;
    • 3, not classifiable;
    • and 4, probably not carcinogenic to humans.
  2. The IARC reached this conclusion despite agreeing that a previous September 2012 scientific study [3] on the ‘long-term toxicity of a Roundup herbicide’ was statistically unreliable. The 2012 Séralini study found that in lab rats ‘By the beginning of the 24th month of testing, 50% to 80% of female animals had developed tumors in all treatment groups, with up to three tumors per animal, whereas only 30% of controls were affected’ This was a study that wasn’t expected to look at cancer outcomes it was to study liver and kidney toxicity from Glyphosate (and it found those too). Scientists debated these findings over several years, the article was retracted in 2013 but republished in 2014).
  3. A June 2013 scientific study [4] found that ‘Glyphosate induces human breast cancer cells growth via estrogen receptors.’ a study that is quoted by Breast Cancer UK who actively campaign for the removal of Glyphosate from the environment.
  4. A November 2016 scientific study [5] in lab rats found that ‘Chronic consumption of extremely low levels of a GBH formulation (Roundup), at admissible glyphosate-equivalent concentrations, are associated with marked alterations of the liver proteome and metabolome.’ i.e. Liver disease.

Now I’m no scientist myself, but if scientists tell me there may be a link between Glyphosate and liver and kidney disease and breast cancer, I’m not going to take any unnecessary risks with my health or that of my family. It’s bad enough that this stuff is in my bread and cereals without me adding even more of it into my diet myself. I would recommend that you take the time to study these reports yourself as there is a lot to digest (more than I can realistically put into a readable article).

Glyphosate can stay in your soil for up to 16 months (not just 2 weeks)
Quite why you’d want to grow your own fruit and vegetables in Glyphosate contaminated soil in the face of those scientific studies I don’t know. You may as well not bother and just carry on buying the chemically treated supermarket fruit and vegetables instead. If you do use Glyphosate on your allotment you should know that Glyphosate degradation is measured in ‘half lives’ – the period of time it takes for HALF of the Glyphosate to disappear from the originally sprayed area. A European Commission study of 2002 [6] found that ‘Under a wide range of climatic conditions found in the U.S., Canada, and Europe, the mean half-life for glyphosate degradation in field soil was reported to be 30 days, with a range from 1 to 130 days.‘ – i.e. it depends on things like rainfall levels to see how quickly the Glyphosate is washed away into neighbouring soil, rivers and the environment but it could take up to 4 months for just half of the Glyphosate to leave your allotment. Monsanto themselves [7] say that ‘detectable levels can be present even after 3 to 4 half-lives, but the concentration in soil will be very low and the residues will be tightly bound to soil particles‘… so it could take as much as a year to 16 months for the Glyphosate to leave your allotment’s soil completely. The produce you consume from a plot recently treated with Glyphosate could in all likelihood contain traces of Glyphosate.

Think of your neighbours, the environment (and those to come after you)
Last year my ageing neighbour sprayed the boundary between his allotment and mine with Roundup weed killer. As a consequence he sprayed my raspberry bushes which promptly died. Not only that but, as he’s slightly further up the hill than me, whenever it rained the Glyphosate would have washed its way down into my own soil. On arrival it could impact upon my earthworms and Mycorrhizal Fungi [8] (which I actively encourage and add to root balls of my pumpkins). Clearly we’re all free to make our own decisions about using weed killer but we do all have neighbours and a responsibility to our environment.

At our allotment association we are contemplating the idea of marking chemical free plots on a site map, and marking the individual plots with ‘chemical free signs’ with the aim of:

  1. Encouraging fellow plot holders not to spray chemicals like Glyphosate or to be considerate when doing so (not spraying on a windy day for example).
  2. Allowing new allotment holders to decide if they want to grow within a chemical free zone or if they’re happy to take on a plot that has been previously contaminated with a ‘possible carcinogen’.

Doubtless the use of Glyphosate will continue for some time whilst it is still available to purchase by the public but I am hopeful that with some education and eventual legislation we may see an end to its use in our gardens, parks and allotments.


1. Soil Association: Glyphosate in our bread
2. Nature journal / Widely used herbicide linked to cancer
3. Springer Republished study: long-term toxicity of a Roundup herbicide and a Roundup-tolerantgenetically modified maize
4. Food Chem Toxicology / Glyphosate induces human breast cancer cells growth via estrogen receptors.
5. Nature journal / Multiomics reveal non-alcoholic fatty liver disease in rats following chronic exposure to an ultra-low dose of Roundup herbicide
6 & 7. Monsanto Backgrounder / Glyphosate Half-life in Soil
8. Nature journal / Glyphosate herbicide affects belowground interactions between earthworms and symbiotic mycorrhizal fungi in a model ecosystem
9. Friends of the Earth – Health and environmental impacts of glyphosate:

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About Author

Matt Peskett is GrowLikeGrandad (if you want to know why read 'About the Editor). He has a few 'heavy clay' allotments and is Chairman of the Dorking Allotment Holders Association (DAHA). Matt also has a medium sized 'sandy soil' hillside garden (Italian terrace designed) and enjoys photography - especially nature. Matt takes inspiration from gardens like Hidcote and Great Dixter and enjoys watching anything on TV presented by Monty Don or Louis Theroux.


  1. Valerie Bebbington on

    My neighbour denied using weedkiller when I asked for its name as I thought it had blown into my garden where my cat ate the grass. The husband also repeated denial a few days later..quite aggressively..
    Apart from my cat, I also have grandchildren in my garden, and often a tame seagull..
    I now have one large dead plant, lots of patches of yellowed grass + since then, the 50/100 or so bees that used to visit have disappeared, and I am also reluctant to harvest any food I’ve grown..
    I’ve suspected my neighbour of weedkiller use in the past but never on this scale.. I have now a number of before + after pics as I often snap our seagull – and its worrying..
    Weedkiller is a toxin + should be notifiable to close neighbours as often its use is indiscriminate + considered harmless by users..

    Regards Valerie

  2. You’re not wrong about the laziness thing. I’m so lazy that I’ve just bought myself a powered weed sprayer so that spraying glyphosate all over my allotment doesn’t take too much effort.

    Also, the US Environmental Protection Agency states “No risks of concern to human health from current uses of glyphosate. Glyphosate products used according to label directions do not result in risks to children or adults.”

  3. Brian Thwaites on

    I have just been offered a fairly large allotment (I think 300M2 is large anyway) which is badly overgrown. and has been or some time. I am 66 with hip damage and there is no way I can clear it without chemical assistance.
    I while I do not trust anything Monsanto says or publishes about their products I may well have to use Roundup to exterminate the overgrown weeds on the whole plot. Having said that I recognise a duty to prevent as far as possible overspray onto adjacent plots. Fortunately there are fairly large hedges surrounding my plot which should limit that possibility as will spraying only on still days. Even then wherever possible I will use opaque none woven weed matting to kill off what I can before probably rotavating the growing beds.

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