# how long for 'Round-up' to work? **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2012, 12:22pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704 "2012-05-22T12:22:38Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [May 22, 2012, 12:22pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/1 "2012-05-22T12:22:38Z")
I sprayed some glyphosate on some weeds a couple of days ago. It doesn’t appear to have a great effect yet. I diluted it to 2.5% which was about the middle range of the chart given with the instructions. It wasn’t really clear what concentration I should use for my weeds, so I just picked something in the middle. WIll it take a week or longer to killl the weeds, or should I consider 2.5% isn’t enough and respray with higher concentration? ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 22, 2012, 1:21pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/2 "2012-05-22T13:21:44Z")
I’ve never diluted Round Up before, but I’ve always bought the kind in a spray bottle - are you using a concentrated version that the average weekend warrior won’t find at the hardware store? You should see weed death happening in a day or two, depending on the particular plant. Some plants with tough waxy leaves such as the ivy that was trying to burrow through my brick walls may need two or three applications a few days apart to see any effect. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [May 22, 2012, 1:25pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/3 "2012-05-22T13:25:58Z")
Give it a week. Glyphosate’s kinda slow, and more doesn’t speed it up appreciably. ---
**Author:** ![Kansas\_Beekeeper](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@Kansas\_Beekeeper](https://boards.straightdope.com/u/Kansas_Beekeeper)\ **Post date:** [May 22, 2012, 1:29pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/4 "2012-05-22T13:29:41Z")
I use 5%. It takes a week, or even a little longer with tough weeds. ---
**Author:** ![sidecar\_jon](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@sidecar\_jon](https://boards.straightdope.com/u/sidecar_jon)\ **Post date:** [May 22, 2012, 1:37pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/5 "2012-05-22T13:37:18Z")
I used it on brambles and they took a few weeks to expire, they look sick and wither rather than out and out keel over. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [May 22, 2012, 2:44pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/6 "2012-05-22T14:44:44Z")
2.5% is a strong dose for most weeds. poison ivy or trees may need stronger repeated doses. also the larger the plant (including root) the more doses it might take. it is an all depends on the plant and conditions. you should see the plant yellowing in 3 to 7 days. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [May 22, 2012, 4:08pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/7 "2012-05-22T16:08:16Z")
I usually see die-off in 5-7 days for most common weeds. I use, according to the directions, 2.5 ounces per gallon, which is 1.95%. > [@johnpost](#): > > poison ivy or trees… Ordinary Round-Up doesn’t do much on brush or woody plants. I think they make a variety for poison ivy, and Brush-B-Gon is supposed to do pretty well on those. I haven’t tried it myself. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [May 22, 2012, 4:11pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/8 "2012-05-22T16:11:19Z")
For me it works in 3 to 7 days when applied in warm, sunny weather. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [May 22, 2012, 4:30pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/9 "2012-05-22T16:30:54Z")
Grass will be dead and brown that afternoon. Ironically, actual weeds do take longer. I agree with what the others have said - a few days to a week to see effects. Some of the weeds I spray seem to simply not thrive rather than outright die; they don’t go away until something else grows on top or I whack them down. One thing I’ve noticed is that weeds with access to a lot of water (like the ones in the swampy green belt behind me) are much more resistant than those in dryer areas. For **gotpasswords** , the spray bottles of RoundUp that they sell at the store are already diluted to the usual strength. Most of the good stores will carry a small bottle of RoundUp concentrate - a couple ounces per gallon of water will give you about the same strength as the pre-mixed spray bottles (and at about a tenth of the price). ---
**Author:** ![Antigen](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Antigen](https://boards.straightdope.com/u/Antigen)\ **Post date:** [May 22, 2012, 4:40pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/10 "2012-05-22T16:40:40Z")
> [@CookingWithGas](#): > > Ordinary Round-Up doesn’t do much on brush or woody plants. I think they make a variety for poison ivy, and Brush-B-Gon is supposed to do pretty well on those. I haven’t tried it myself. I’ve used Brush-B-Gon on poison ivy - it’s the only thing I’ve found that works. It takes a week or more for the plants to die, but they do die. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 22, 2012, 4:57pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/11 "2012-05-22T16:57:03Z")
> [@Antigen](#): > > I’ve used Brush-B-Gon on poison ivy - it’s the only thing I’ve found that works. It takes a week or more for the plants to die, but they do die. Same here. Like the others, I don’t expect to see results from weed killer for a week. Even then, many of the plants slowly turn brown before withering away after another week or more. ---
**Author:** ![MeanJoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/meanjoe/32/5693_2.png) [@MeanJoe](https://boards.straightdope.com/u/MeanJoe)\ **Post date:** [May 22, 2012, 8:23pm UTC](https://boards.straightdope.com/t/how-long-for-round-up-to-work/622704/12 "2012-05-22T20:23:28Z")
Nothing more to add that hasn’t already been said - 7-10 days is what I usually see in my area and I use the concentrate and mix with water. A slow wilt after a few days to eventually a brown, crispy weed. As mentioned, grass tends to die very fast when I accidentally over-spray. (Whoops!) I also find it has to become a regular maintenance thing. Round-Up, Scott’s TurfBuilder, Preen, etc., to take a more broad strategy for fighting weeds and slowly reducing the percentage that return to trouble areas.