Friday 30 November 2012

Using glyphosate (4)

Using glyphosate to eliminate weeds from an overgrown plot before making a new garden

Knapsack sprayer
If you have not been reading my previous posts it may be best to press these links now.

Although I spray with glyphosate all year round provided that the weeds have an active green top, many perennial weeds have died down now and in late November it will be useless to spray. Best to wait until the weeds have made a strong head of growth in late spring. If you have still growing green weeds in a temporary open space it will be alright to spray. Similarly if you want to spray-off an old lawn or rough grass sward to make a new garden feature it can be done anytime. I despair when gardeners strip off old turf and throw it away. Far better to leave  all that wonderful dead root fibre in situ.

Glyphosate maths for dummies
If you are using an amateur product the label will explain clearly how much to use. I find many gardeners when using a commercial formulation are confused because instructions  are expressed in litres/hectare. If like me,you are worried about losing a decimal point in your calculation for a small plot, the maths becomes easy if you remember one litre per hectare converts to one ml. per ten  square meters. In point of fact such information is useless to me. For my own purposes it is the strength of the diluted spray that counts. Almost invariably I dilute commercial product (360 gm/ litre concentrate strength) at a rate of 20ml/litre i.e. 1:50 dilution. I only rarely exceed this. Please note for all pesticides there is a maximum permitted dose per unit area.

The village plot is owned by the village community. It was the site of alms houses demolished thirty years ago
Clearing Seaton Ross village plot
Five years ago the plot was a vigorous stand of ground elder, bindweed, couch and much more. It took a year  for my knap-sack spraying to almost clear the plot, another year to completely eliminate the ground elder. In that first year I sprayed four times.
  • My first spray in May was strength 20ml/litre. Subsequent sprays 15ml/litre.
  • I use my ‘directional’ spraying skills to spray at a fairly low pressure to evenly wet the leaves of the weeds just short of ‘run-off’.
  • In recent years I have come to prefer a cone nozzle (rather than the normal anvil type) on a partially extended lance. I do not walk in straight lines with my spray-head  held rigid. I more ‘duck and weave’ and for example I lowered the spray head almost to the ground to spray in a downward direction under and beyond the perimeter hedge.

Five years ago this hawthorn was being strangled by convolvulus (bindweed) and ground elder. It is now cut twice a year by Peggy (Mrs. Seaton Ross) and has been under-sown with fine fescue grass, also cut twice a year.

  • The village plot area is a fifth of a hectare. It took about an hour for my first spray and I used the contents of a full 15 litre sprayer. It’s a good idea for an inexperienced sprayer to practice at first using pure water!
  • It was nearly three months before I sprayed again. It is essential that regenerating weeds are given time to make some new top. It is useless to zap weed immediately it reappears!
  • As I expected by the time of the second spray there were new perennial weeds that had been shielded from spray by the previous weed canopy.
  • The death of the cover of perennial weeds lets sunshine penetrate to the soil below. This is a great opportunity for many  thousands of weed seeds that lie near the surface to germinate, their enforced dormancy broken. Much of the need  for subsequent spraying is to kill them before they self-seed.
  • In the second year of my program I started to slot-in expendable ornamental plants and scatter seeds in newly clear spaces. My spraying now becomes even more directed, more like the ‘spot spraying’ I do in my cemetery gardens. I do not spray bare soil.
  • By the end of the second season no perennial weeds were left.

These mildew resistant forget-me-nots will be a beautiful blue carpet next March. Early in the  project such plants would have been expendable if ground-elder had appeared in their midst.

An apology…
to those of you who do not use a professional knapsack sprayer. It is quite easy to clear a plot with a just a small hand sprayer. It’s just harder work, takes longer and is less accurate. For years my maintenance spraying in Bolton Percy churchyard was with a hand sprayer. If I felt particularly mean, I even used a recycled domestic sprayer!

2018 update I would not contemplate this now and emphasise buying a quality professional knapsack sprayer is the best investment anyone with a medium size garden can make - so much easier and far more accurate. One like the picture I have added to the top!


  1. I found glyphosphate effective for many weeds, including bind weed (needed two applications), but less so when we bought a house which had an infestation of mare's tail (I didn't even know what it was when I first saw it). In order to get rid of mare's tail (and lessen the likelihood of it coming back) I eventually used the a high strength brush-wood killer and one of two following methods
    1. Carefully rough up the mares tail a little (say between two blocks of wood) to break the waxy surface without snapping it off before appilcation of the weedkiler.
    2. Apply normally and then cover with something (say half a plastic bottle).
    These both overcome the problem that Mare's tail has a waxy coating which doesn't get penetrated well by the weedkiller before it dries.

    Using the top half of a drinks bottle is patricularly effetcive for spraying weeds in close contact with plants since you can put the bottle over the weed, unscrew the cap, spray the weed and then replace the cap.

    1. Very helpful comment Anon. I have used similar methods myself and in due course will be blogging about them. Mares tail is a notoriously difficult weed! It is great when folk put their own tips on the blog.
      I am preparing a post on using glyphosate selectively

    2. Mares Tail needs SBK or similar hormone spray. This will not damage grass. CEW


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