How long between spraying Glyphosate and the Glyphosate "getting in place" to kill the plant.

My issue is this - I want to make productive use of an area overrun by very well established weeds - and only have 3 days in which to prepare the area and get my weedmat and plants in place. I can't really pull the plants out by hand - the roots are too well established and there are too many of them.

I know that glyphosate takes some time to actually kill the weeds, but I'm wondering if the glyphosate will penetrate the plant within 24 hours such that if I cut the foliage down to ground level (and cover with weed mat) it will "stay dead" and allow me to plant my new plants through holes in the weed mat without overrunning my tender seedlings ?

  • Are you planning on a food crop? Listen to Bamboo, this stuff will not get rid of weeds within 3 days, forget it. And you won't be able to replant for 3 weeks (ideally). There are far better ideas if you've got an area of weeds (and weed seeds, don't forget, that glyphosate does not kill). Quit worrying about weeds, they are there, will be there and can easily blow in. if you put down 'weed fabric' I will be pissed! That weed fabric was never meant for weeds, it was meant to keep gravel from sinking down into the soil profile. Weeds are not a deal breaker...far better control methods.
    – stormy
    Oct 22, 2016 at 23:04
  • Dig that ground up, add topsoil, make RAISED BEDS out of just double dug soil. Plant a cover crop for the fall winter and early spring that will negate weed growth, weed germination to be turned under for organic matter in your plant beds. Weeds are just fine for organic matter to feed your soil. And mulching thickly with DECOMPOSED organic matter (compost) is far better than any plastic...that fabric just makes me mad! Talk about screwing up your soil and micro, macro organisms that are necessary for plant growth!!!
    – stormy
    Oct 22, 2016 at 23:08
  • Just leave the weeds in situ and do a no dig bed. Leave the roundup where it belongs, in its container. Weed mats are not necessary and don't work. Jul 28, 2018 at 10:39

1 Answer 1


Glyphosate is systemic in action - that means it takes about three weeks to kill a plant, but with the added proviso that it's at its most effective as a weedkiller if applied when weeds are growing strongly rather than when they're slowing down because of the approach of Fall, or because the ground is dry and they're short of water. Well established weeds will very likely need more than one treatment, so I'm afraid glyphosate will be ineffective if used in the manner you describe, that is, spraying and then cutting down the topgrowth within 1-2 days, see here http://www.weedkiller2u.com/weedkiller-faqs

If you want to plant out so quickly, the only viable option is to dig out the weeds, complete with roots, level off and then plant.The other point is, if what you're planting are food plants, particularly root crops, there is strong evidence to suggest that, in some soils, vegetables such as carrots will retain glyphosate within their structure as they grow - it won't kill them, but it will be present in the vegetable on your plate, despite the claims of the manufacturers of Roundup that it somehow disappears completely once it hits the soil. In fact, it becomes technically inert, meaning it shouldn't kill new plants put in after application, but may end up in whatever you're growing, particularly if you replant so quickly after application - this is not necessarily important for ornamental plants, but is important if you're growing edibles.

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