I stopped at a local Garden centre for a coffee last week and was astonished to see a Roundup promotion displayed under the banner ‘Rapid action weedkiller’. Was the manager ignorant of his product or subtly hiding the truth without actually lying. It then struck me that within the deception they hid a great truth.
You may very well remember a few years ago an advertisement for a paraquat based herbicide that favourably compared their product by quite rightly claiming it is much quicker than glyphosate. They showed parallel weedy strips of a long garden sprayed with these two very distinct - and actually incomparable products. Paraquat works by a contact action and if the sun is shining rapidly kills the leaves and green tissue. Glyphosate is translocated from the leaves to the roots and thereby kills the complete plant, but it does take much longer for the leaves to die. No doubt the advert actually showed a pure stand of annual weeds, a very unlikely occurrence in most gardens where a mixture of different types of weeds are more usually the problem. The advert showed paraquat killing all the weed by the next day, but in the glyphosate sprayed area there was no effect whatsoever several days later. This clever advertisement correctly confirmed that glyphosate is slow! It did not of course clarify that paraquat does not kill established perennial weeds. Its action is to kill the tops and it is sometimes described as the chemical hoe.
Before I explain the great insight inadvertently uncovered by my local Garden centre let me describe glyphosate’s actual speed. If sprayed in hot balmy Summer weather it might be possible to discern glyphosate has been sprayed after a couple of days. Perhaps after a week delicate small weeds might be dead. After a month the tops of tough perennial weeds might have demised. In colder conditions you can at least double these times. In a very cold Winter it might take more than two months! (And although glyphosate can be used in Winter as explained in this post, if weeds have lost their tops it has no effect whatsoever)
|A week of warm sunny weather after spraying a garden in France.|
Although young weeds will normally be completely dead with a single spray after the times given in the above examples, this is not true of established coarse vegetation. If you are very lucky and you are spraying glyphosate onto intact vigorous couch grass for example, you might kill it in one go. Much more likely where gardeners will have previously scrabbled around trying to mechanically remove roots and the herbicide-receptive green leaves have regenerated erratically it will take several applications over a season. Should you have a problem-weed such as ground elder you might have to respray half a dozen times over a couple of years. When I originally sprayed off the weeds in Bolton Percy Cemetery they had been undisturbed for twenty years and amongst all manor of noxious perennial weeds were horseradish roots thicker than your arm and two spits deep. It took me a couple of years before I started seriously planting.
Some vegetation is difficult to kill because it is well established, other vegetation does not die because it is herbicide resistant. Difficult weeds such as nettles need a stronger spray but within the regulations. It is thought that many weeds are less efficiently killed if the glyphosate is too strong.
The general pattern is for the tops of tough weeds to die and then for the plant to make new growth from the ground. It is no use zapping small new leaves because they will have insufficient surface area to absorb enough weedkiller. Wait several weeks before you respray.
Another reason for initial failure to kill weeds on an overgrown site is that low growing weeds are sheltered by taller vegetation. Some weeds have different patterns of leaf growth and dormancy and may not be receptive to spray. To the more experienced sprayer such variations are means of gaining selectivity between weeds, wild flowers and garden plants.
In what sense is glyphosate quick?
I gained my love of the soil when forking out couch grass rhizomes in my parents’ new garden when I was fourteen. (That is if you discount making mud pies with Christine when I was two!). You have never seen such a luxuriant stand of a single weed over the whole of a garden. The previous occupants had rotavated the garden once a year! What a superb method of inadvertent unwanted propagation.
In the first year by repeatedly forking-out, I eliminated the couch over a third of the garden. For the rest it was too much for me and I changed my strategy to very frequent deep hoeing of once-dug soil. The idea is that by persistent hoeing, perhaps every nine days, that the underground rhizome’s supply of carbohydrates and buds are exhausted! Both methods work well if you are sufficiently diligent.
Some years later my friend Brian acquired his first home and a very weedy garden. I told him about my method of eliminating couch. We moved away and I did not see him for another thirty years. I eventually re-established contact. “Remember your method of eliminating couch”, he declared, “I am still hoeing and it’s still there!”. None gardeners spend years failing to control perennial weed and it is not quick.
My parent’s were reluctant weekend gardeners before they moved to the couch garden. At that time I had no interest what-so-ever in matters horticultural! Some weekends they would feel impelled to sort out the garden! They would start at one end - always the same one - and would laboriously work their way round pulling out luxuriant weeds. If their energy levels permitted they would get completely around the garden over the weekend but this was rare. It was such a laborious task they waited as long as possible before starting again. Not only was their work unpleasant and daunting it took many hours and and over the years never ended. How quickly the yet-to-be invented glyphosate would have permanently eliminated perennial weed so that weeding would have become bliss.
Another sense in which ‘Roundup’ is quick is that the man-hours in applying the chemical to a garden are very few compared with traditional weeding. It might take a year or more to rid of difficult weeds but the actual time spent working, even if you start with an overgrown acre, is very small.
My own garden is about an acre and is very intricately planted. In Summer it takes me three hours to completely spray round and I might do so every fortnight. At other times of the year it might not be so frequent and in Winter I might get round with my knapsack sprayer in as little as an hour. I have created a rod for my own back in creating a large and intimate garden. Should I ever sell it I will have devalued my property by thousands of pounds. Prospective buyers would look at it and tell me it was a fabulous garden before they walked away. Using their own methods there would not be enough hours in the day to maintain it! For me glyphosate is quick.
|A rod for my own back|
|An exciting new canvas|
|Making Cathi’s garden quicker to mow and plant|
Sometimes in a garden there may only be a light cover of newly germinated weeds and one may wish to do some sowing or planting. Perhaps one might be using stale seedbed technique for sowing a new lawn. A day after spraying glyphosate the weed is still green but is ‘as good as dead’. There is no reason not to go ahead and plant or sow. With dense or well established weed this is impractical and there is a very small theoretical possibility that contact with dying weed might contaminate your plant. I frequently glyphosate-spray a section of my vegetable garden a few hours before sowing or planting
‘Roundup’ the story so far.
When I started my blog I wanted to share my experiences of using glyphosate for nye on forty years. Very little reliable information is available for amateurs and if you attend a college special course you will learn much about farming, engineering and regulations but nothing about actually how to use glyphosate in a garden!
As a purist I used to always use the word ‘glyphosate’ in my titles because it is the correct chemical name. I have now given in and accept the whole world now uses the word ‘Roundup’ as a generic term. Not only do I get more ‘hits’ for my own personal satisfaction but more gardeners now find me!
I do not wish to encourage inexperienced new gardeners to go ‘gung ho’ into using glyphosate in a lovely garden. They will have far too many disasters. Although I have much more to say about glyphosate I have now covered the basic techniques. To use glyphosate safely you need to read all of my glyphosate posts! Unfortunately my early titles do not all always disclose the article’s content. To find relevant posts insert ‘glyphosate’ or for more recent ones ‘roundup’ in my search box at the bottom of the blog. This finds them all!
The smaller search box at the top very left hand corner takes you directly to specific articles that Google deems a ‘best match’.
|I think it quick when I spray half an acre of the village plot in one hour|
|Worsbrough cemetery covers three acres. I spray alternate halves each succeeding month with my knapsack sprayer. I think a total of six hours is quick|
|Someone on Costa Rica knew that Roundup was the quickest way to clear this site|
More musings on glyphosate’s speed of action
There are too many variables for me to say how quickly glyphosate actually kills weeds. Apart from temperature and humidity there are factors such as accuracy of cover, dose, how long glyphosate remains on the leaf before it rains - and sometimes very light rain even enhances its action, sturdiness of plant, nature of the leaf surface and actual plant resistance. As mentioned it will not kill some weeds in one go. In these cases leaves and tops will usually yellow, go brown and die before new growth regenerates from the ground. It does not always work out quite like this. Some weeds might go an awful yellow and suddenly shrug off the herbicide effect, miraculously re-green and start to regrow. Last year I was very grateful of this effect when I carelessly sprayed a couple of gentians having thought they were darned epilobiums. Six months later they flowered as well as their unsprayed companions!
|The same species of gentian but not the same plant!|
|Dying large weeds look ugly and get ‘roundup’ a bad name. Where weeds have newly come from seed it is best in visual terms, to spray when they are still small.|
The advice on the caption does not apply when there are vigorous very well established perennial weeds when a very large leaf-area is needed for the spray to be effective.