Thursday 6 June 2013

6 Using glyphosate selectively

Unless you look very carefully you will not see sprayed weeds in my garden
I could not manage five acres of gardens without using glyphosate. I have explained in my previous posts how I have created diverse and naturalistic plantings of thousands of  healthy plants. I have also tried to show how my gardens provide rich habitats for wildlife. I know many of you do not agree with using glyphosate and I respect your view but for me it is an essential part of what I do.
I believe ‘Roundup’ is a most useful tool to create and maintain beautiful gardens  and the purpose of this series of posts is to share with fellow gardeners my experience of using  glyphosate over the last thirty years. So far I have described the ‘easy bits’ such as clearing an overgrown plot, clearing fence lines, spraying under coarse hedges, spraying pathways and drives and rough-grass edges inaccessible to mowers, spraying between widely spaced shrubs and under trees. All to varying degrees, are selective methods based on the directional action of the spray. Glyphosate does not know the difference between a plant and a weed. It potentially will kill them all!
There is a fine balance in the care needed when using glyphosate. I find to my horror some men just stand there and vaguely direct their spray in the hope that magically the weeds will be killed and the plants will not. Equally perplexing are those gardeners who faff around spraying a square meter in the time I spray a small garden! There is a happy medium!

It takes less than three minutes to spray my ‘acid border’
It is no secret why the horticultural press say little about using glyphosate among plants. Not only is it of no interest to most gardeners, in inexperienced hands it is an unfortunate way to damage and kill  plants. Too many things can go wrong! I am sure you have all seen ‘Roundup footprints’ across the lawn. I will go further. I do not want to persuade inexperienced gardeners to spray among delicate plants at all!  What I do want to do is to provide guidance for those who choose to spray to do it well.

Two of the main methods to achieve selectivity with glyphosate are the use of directional application and timing. An example of the latter is when bulbs are dormant you can safely spray above them, more about this principle in my next  glyphosate post!

There is no need to spray my herbaceous border now as the plants grow so close together but it would be ideal in winter
Although  counter-intuitive a professional knapsack sprayer with a long lance is the most accurate way to spray. It is important that the sprayer has a trigger to stop/start application and that the pressure can be adjusted by the pump handle to everything between a mere dribble and a full thrust of spray.
I found it completely inappropriate for ‘spot spraying’ the way our students were taught to spray by agricultural engineers who worked to professional specifications. They were taught to spray with almost continuous  liquid flow at constant pressure. (I once mistakenly bought a knapsack fitted with a constant pressure device and immediately threw the device away). Such methods are appropriate to agricultural situations where large uniform tracts need to be  sprayed accurately per unit area. The accuracy I am interested in is to kill the weeds and not the plants! 

Tips to achieve accurate directional spraying with a knapsack sprayer (spot spraying)
  • Only spray when there is no wind and it is absolutely still. Early in the morning is frequently best. Having said this many amateurs fear to spray in a light wind when their spray can be delivered safely at low pressure when the spray head is held low
  • Direct your spray down and/or angle it away from your garden plants.
  • The nearer the spray nozzle to the weed the greater the accuracy.
  • Vary the spray pressure with circumstances. For a few isolated weeds direct the nozzle close to the weed and give little more than a squirt. For larger weedy spaces hold the nozzle a little higher and pump a little harder.
  • Do not spray at too high a pressure. I usually achieve sufficient pressure with two to four thrusts on the handle - maintained by a single thrust as the pressure subsides. In truth, I find it difficult to describe what I do, it is so instinctive and varies with circumstances.
  • Do not attempt to control pressure with the trigger. It should be either, off or on!
  • Although it is wasteful and normally counter productive to spray to ‘run off’ I am quite happy for this to occur when spraying a rosette forming weed like epilobium in winter when ‘stem flow’ will direct it to the roots. Although leaving no horticulturally significant residue in the soil, glyphosate will be absorbed by basal roots for a little while.
  • Although it is normally alright for the bark of woody garden plants to be wetted any green plant tissue will absorb weedkiller.
  • Do not spray anywhere near soft actively growing plants. Unless you are exceptionally skilled the best weed control in your vegetable garden is with a hoe!
  • Normally use the glyphosate at the lowest recommended dilution.
  • Practice first. I once had a colleague who found his former employer expected him, on his own, to control weeds in a small park. He taught himself to spray accurately with pure water in his knapsack and carefully sprayed around upturned plant pots on a concrete surface. When he could wet the concrete and not the pots he rightly concluded that he was ready to spray!
  • Spray shields over the nozzle are often recommended and some gardeners swear by them. Personally I never use them. I prefer to see what I am doing!

Getting Roundup a bad name
Although to kill established perennial weeds they need to be allowed to make a full head of foliage, this is not the way to tackle ‘weeds from seed’  which should be sprayed when very small. Otherwise you get a mess like the above! The casual observer never sees sprayed weeds in any of my gardens.

Anyone unfamiliar with glyphosate spraying should read all these previous posts before attempting selective spraying.

If you read this post you might doubt my competence to spray.

This links to control of ‘weeds from seed’


  1. Those garden photos are beautiful a testimony to your methods. Fortunately with my small garden weeds aren;t a problem but we do use Weedol on the plot!

    1. Yes despite my comment about the veg garden, their is scope for herbicide in the veg garden out of the growing season and where there are large gaps

    2. We tend to use it for things like docks in fruit beds or on unplanted areas not where vegetables are growing. We had problems with herbicisde contaminated manure a few years ago and so are wary to start with.

  2. Roger, I think like most things in life, if weedkiller is used wisely it will be fine, but in the hands of a reckless amateur it can be lethal.

    1. I tread a fine line blogging about weedkillers Mark. I dread a complaint about someone having a disaster after following my advice!

  3. Great informative posts! I use Roundup on my paving and gravelled paths, and have had a bit of a headache how to spray close to the wooden border that goes all round the path. I have plants growing close to the wooden border in all the beds and their roots might very well stretch out under the gravelled path, so my question is; can Roundup applied to one plant on the surface get to the roots on another plant underground?
    I have a weed liner under the gravel, but right on the edge there often end up growing some weeds after all. Up until now I have resorted to pull them up or dig them up by hand.

  4. Roots grow a long way Helene, there will be plant roots under your path and your path weeds may well grow into your border. The whole of my spraying for the last 30years is based on the assumption that there is no root transfer between weeds and plants! For practical purposes there is no transfer. The transfer that worries me is when I have not been quite as accurate as I intended!
    There was a little speculative discussion on this blog several months ago whether glyphosate might transfer via mycorrhiza but I know of no research which demonstrate this. I claim that in general the health of my plants is excellent.

  5. Interesting post Roger - your garden is gorgeous. Private homeowners are not permitted to use any herbicide or pesticides in Ontario for cosmetic purposes. Our lawns and gardens certainly aren't looking as good as they used to. The old adage of good, fast, cheap - pick two - certainly applies, I'm spending more time weeding with poorer results. With the chemicals taken away, it certainly has changed the way I think about gardening.

    1. Wow and here I was thinking our own authorities restrictive. I did not associate 'big brother' with your country.
      If push came to shove I could manage without all pesticides other than glyphosate!
      Best of luck with your weeding Barbara

  6. Message for Molly!
    I received my usual e mail confirmation of your comment on this post. But it hasn't appeared. I have noticed that sometimes comments from an i pad do not always appear.
    Anyway best of luck with your 3 acre garden!

  7. Hi
    Have you noticed the reports of glyphosate being found in the urine of Europeans in 18 European states?

    I enjoy your blog very much. Thanks.

  8. lyphosate, the active ingredient in Monsanto’s Round-Up, is attracting a lot of negative attention these days, this attention is not without merit. Within the past 6 months alone, there have literally been dozens of studies published illustrating the hazardous impact glyphosate is having on the environment. From earthworms to humans, this herbicide, once considered safe, is proving to be quite the silent killer.

    1. Thanks Peter and Shallowal for making your points in a sensitive and none combative way. I might very well do a future post about my attitude to such issues and recent research.
      I try in my blog to show how when used properly glyphosate can be beneficial to the environment and wild life and that indeed in world agriculture the use of the minimum cultivation it facilitates is good for the environment and soil fertility. Until I find it shown to be otherwise, I certainly suggest that because of minimum cultivation there are far more earthworms on this planet than if glyphosate was not used and they were destroyed by cultivations.
      Sorry I am sounding flippant now which is not my intention. These are very important matters you raise

  9. You are most welcome Roger, my input has stemmed strangely enough from a very long story. Which all started from helping my mother (75) I helping in new ways so she can continue gardening. For the record I am not a gardener in the traditional sense. My skill set is more Hydroponic & Aquaponic based.
    I have introduced vertical gardening into my mums life and moved her away from chemical fertilizers to organic. In my research of pesticides & Fertilizer I have found alarming news and evidence which is being talked about globally. There are many natural options which i have found very interesting and new ways of doing things which really do not require any chemicals at all and actually provide higher yields than traditional gardening.

    Thank you for you Blog I really enjoy it.

  10. Thanks for the reply. I asked the question as I think you will reply with considerations I hadn't even thought of! Although I try to garden as organically as I can, I do use glyphosate around the edges! (but not in the veg patch!). I look forward to any of your thoughts!

    1. Hi again Peter,
      I am a little reluctant to enter any debate about this particular piece of research of which I have no special knowledge, but you ask for my thoughts and here they are
      I am disturbed that glyphosate has been found in human urine.
      Given the extremely wide use of glyphosate in just about every form of agriculture and horticulture across the world I am not surprised.
      Modern techniques of detecting minute traces of a chemical are hyper sensitive and levels of chemicals orders of magnitude below potentially toxic doses are frequently found in testing generally.
      I am sure I would be shocked at all the other minute levels of far more toxic materials in my own urine albeit that I go out of my way to live and eat healthily!
      This piece of research does not demonstrate any harm caused by the chemical.
      Approvals for chemicals such as glyphosate involve feeding very high doses of chemical to test animals ( procedures of which I am not comfortable with). Glyphosate has been shown to have remarkably low mammalian toxicity.
      The fact that it is found in urine does demonstrate the body is doing its job and is flushing it out - unlike DDT which was notorious for building up in fat tissues.
      I have no personal worries about my own health from this new information.
      I expect many hysterical reports of this new information, although I do not doubt the veracity of the research itself. (nor will I be entirely happy with the ‘spin’ that will be put on this story by promoters of glyphosate).
      I see nothing in this which at the present time will change my own attitude to using glyphosate.

  11. where can I buy glyphosate at a good price

    1. I have done a number of posts on glyphosate anon, If you use the search feature at the bottom of the blog and put in 'buying glyphosate' you will find my post that makes suggestions. The basic answer is buy the commercial product on the net and use it according to the dilutions I quote - search for that too!

  12. Hi. Love this blog, and have been drawing on your experience in trying to learn about how to keep up the beautiful garden that came with my new house.

    One question - plants that spread by rhizomes - if there are a few new shoots coming up a little away from the main plant, and you spray them - what is the likelihood of killing the main plant?


    1. Difficult to answer Ronan without knowing circumstances. I am fairly cavalier about spraying to reduce the size of herbaceous clumps of vigorous plants spreading too far and spray vigorous things like helianthus at the margins in Spring if they are spreading . Even yesterday I sprayed part of my clump of gardener's garters where it was invading a michaelmas daisy!
      However with more delicate plants there are dangers and rhizomes and stolons of some grasses and mint(!) are very sensitive to glyphosate and might be damaged from a distance. Raspberries too are sensitive to their suckers being sprayed at a distance

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  14. Your last picture is a give-away to those who mind that glyphosate has been used.
    With our park gardening group we try to be very discreet so at what stage is it ok to remove the dying weed do you have to wait until it is completely brown?
    Our weeds are mainly grass and chickweed also hoary cress which we usually paint with wallpaper paste thickened glyphosate as it will come up in the middle of other plants.

    1. That picture was in Costa Rica and particularly ugly!
      For the weeds you mention (assuming the grass is an annual one and perhaps the cress hairy bittercress?) I would if it is closely intermingling with soft vegetation just pull it out- especially as it sounds you are intending to do that anyway!

      The same weeds growing in spaces I would just carefully spray - the wallpaper paste is very fiddly - although excellent for spot treating difficult perennial weed.
      To actually answer your question, you could perhaps pull the weed out after three or four days.
      In the dry windy weather we are having at the moment hoeing is very good against small annual weeds.
      It's great to hear about your volunteering - I bet you all love it!


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