Best time of day or weather to spray weed control like Round up or Weed B Gon.

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I remember someone mentioning there was a better time to spray so that the green leaves absorb the liquid but I cannot seem to find it in the archives.
  34 answers
  • 360 Sod (Donna Dixson) 360 Sod (Donna Dixson) on Mar 19, 2012
    If you are spraying lone weeds (as in not on top of your lawn grass) Round up works better if the ambient temperatures are between 60 and 85 degrees F. Weed B Gone has a different active ingredient (2-4d) ,which you can spray over Bermuda grass at the current temperatures. It will activate faster at a lower temperature than the glyphosate(round up) active ingredient. When temperature go above 90 you are taking a risk using any weed killer because the air will move it around where you don't want it to go.

  • So time of day does not matter? Plants are not more likely to say absorb moisture through leaves in morning vs evening vs noon? Just asking. I've sprayed some a few times but trying to get the most "kill" for my effort. The temp info is great. Thanks!

    • Randy Cline Randy Cline on Jul 18, 2017
      Yes, Kevin, time of day does matter. The best time to spray is when weeds are on the uptake of water. This is early morning before the sun is up.

  • 3po3 3po3 on Mar 19, 2012
    Yeah, I have always read that it should be applied in moderate temperatures and less wind and rain.

  • We always recommend spraying weed killer after the morning dew has dissipated. That way you are not diluting the chemicals even more than they already are. The temperature is also important and we suggest the same as Four Season Nursery did above.

  • Robin W Robin W on Mar 20, 2012
    The best time of day to spray weed killer is NEVER! Pesticides are carcinogens and neurotoxins and do not belong where other living things are. Investigate alternative weed controllers, such as vinegar, boiling water or mulch.

  • John T John T on Mar 20, 2012
    ..there are some control products that use natural sources. Best time for broadleaf weeds is Fall when they are storing up nutrients for the winter.

  • Barbara R Barbara R on Mar 20, 2012
    Never! This stuff is not selective on plants that it kills and though it says otherwise, it can be toxic to pets and humans. Consider mixing a gallon of strong vinegar with 2 ounces of orange oil plus a squirt of dish detergent. This is a natural herbicide that may take more than one application but is much safer than chemical herbicides. It works best during the sunniest, hottest part of the day.

  • Donna Marie P Donna Marie P on Mar 20, 2012
    Vinegar works very well ... a great alternative to chemicals

  • Joan W Joan W on Mar 20, 2012
    Please be kind to the earth and don't use Round Up or similar products. With all the info online recently about the evils of these products and what Monsanto is doing, please research and be a responsible gardener.

    • John John on May 12, 2020

      how else can you control weeds in yards that are only occupied for brief periods of each week

  • Angela K Angela K on Mar 20, 2012
    @ Donna, do you use white vinegar, do you spray it on, & does it hurt grass or shrubs?

    • See 1 previous
    • Mike Arriaga Mike Arriaga on Apr 07, 2020

      To be clear, both the natural vinegar method and the roundup method are for killing EVERYTHING it makes contact with! Example: for use on weeds growing between cracks in concrete or in driveways or anywhere you want complete elimination. Both methods ARE NOT for spraying on your lawn fir weeds!!!!!!

  • Mary M Mary M on Mar 20, 2012
    what natural alternative do you suggest for killing poision ivy or poison oak?

  • Candy J Candy J on Mar 20, 2012
    Does it matter if it is white or brown vinegar? I really like this idea.

  • Bill B Bill B on Mar 20, 2012
    Spray after dew is gone, no rain or sprinkling for 24 hours,warm sunny temps if possible.

    • Randy Cline Randy Cline on Jul 18, 2017
      The best time to spray is when weeds are on the uptake of water. This is early morning before the sun is up, not after dew is gone.

  • Margy M Margy M on Mar 20, 2012
    I am going to try vinegar tomorrow, I have brown and white. May use both!

  • Darryl D Darryl D on Mar 20, 2012
    The "natural" alternative suggestions are making me want to gag.

  • Brenda A Brenda A on Mar 20, 2012
    Post from Pinterest- 34 oz. spray bottle-1/2 c. salt, squirt of dishwashing liquid,fill up the balance of bottle with PICKLING vinegar.SHAKE SHAKE Shake. KIlls weeds, but also grass and other vegetation. So best to use in areas that you want to eliminate everything.

    • Susan Susan on Jun 02, 2020

      Hello Brenda, I can not find Pickling vinegar. Will white vinegar work just as well?

      Thank you in advance

  • Terrry S Terrry S on Mar 20, 2012
    Kevin, looks like you are a lawyer so you may appreciate hearing that the law requires you to read the label and the label tells you the conditions under which you should spray. I'm not trying to be the weed control police or anything and of course we all know the cops aren't going to show up to bust you for not reading a label. But there is a liability issue you might appreciate. If the label tells you not to spray when it's windy, but you go ahead and spray on a windy day because you didn't know that & the pesticide spreads over to your neighbors prize roses and kills them (or worse yet, you do damage in an agricultural area or to ground water) you are liable. Knowledge is power and I really recommend reading the label for your own safety as well as the sake of everything around you. If the label on the container isn't readable they are all available on the net these days. Vinegar users also need to be careful. Just because it is natural doesn't mean it can't hurt you if you have sensitive skin. Do not use more than 5% acidity (normal household stuff). Vinegar is broad spectrum which means it kills whatever it comes in contact with, including shrubs & grass. Vinegar only kills topically. Spray it on a leaf, especially in the sun, and it will burn the area it contacts. It will not spread to the roots or to other leaves and kill them, but sometimes the death of the leaf will lead to starvation of the rest of the weed; sometimes not.

  • Angela K Angela K on Mar 20, 2012
    @Brenda,if I want to use in grassy areas or in beds, what should I use?

  • Betty Brady Betty Brady on Mar 20, 2012
    I would not use Round-up. Toxic to everything, including humans. Going green, like using vinegar is better for you and the environment.

  • Brenda A Brenda A on Mar 21, 2012
    @Angela K- BAD NEWS...Your Hands ! I put a book on cd and sit down and commune with nature ! LOL It is a pain but when done thoroughly at the beginning of the season, that takes care of it, for the most part. I always wait and put down my new mulch afterwards, then DONE! I have gravel paths around my flower beds. That is where I use it. Also where you would have pavers.

  • Barbara R Barbara R on Mar 21, 2012
    You can use the 5% or 9% white pickling vinegar found on grocery store shelves. It will probably be plant based. You can also find 20% strength which will probably be petroleum based but is still better to use than Round Up. Add 2 ounces (4 tablespoons) of orange oil plus a squirt of liquid dish detergent. (That helps it stick to the plant.) Use in the hottest part of the day.

  • Margy M Margy M on Mar 22, 2012
    I used a bottle each of white and brown vinegar in a garden sprayer yesterday. It was in the 80's here, and within two hours the weeds were turning yellow. Haven't looked yet this morning. So far so good though.

  • Margy M Margy M on Apr 19, 2012
    Well, the vinegar doesn't kill my tough hillbilly weeds, folks! It stunts their growth a few days but then they come back stronger than ever!

  • Candy J Candy J on Apr 20, 2012
    How would it work on my mulch? Now I have dang grass and weeds growing thru my mulch.

  • Mai185512 Mai185512 on Jun 15, 2013
    Don't plants have different biochemical processes during different times of the day, though? Wouldn't that affect how RoundUp works?

  • Cynthia Cynthia on Jun 20, 2013
    Spray only when it's full sun and not due to rain within 24 hrs. Roundup works fast. Be careful when spraying close to shrubs and flowers. Always best to just pull those.

  • Dale B Dale B on Jun 24, 2013
    I have tried the vinegar solutions and have had limited results. If you are killing tough weeds especially some that tend to be woody or have a waxy coat on the leaves, Roundup brings good results. It is impractical to try to use home remedies when you are doing large areas. Just be responsible and use as directed to prevent damaging surrounding plants.

  • Allen Marsh Allen Marsh on Jun 28, 2015
    How long after rain ends do you wait to apply?

  • Randy Cline Randy Cline on Jul 18, 2017
    Weed killers are absorbed through the leaves. Some of you seem to be forgetting biology class. Weed killers are best absorbed when weeds are on the uptake of water. This is early morning before the sun is up. When the sun is shining, plants are making their food. For those who don't remember, this is a litlle thing called photosynthesis. The person that said to spray after morning dew is gone is wrong. If you do, there is less chance that the weed killer will be absorbed

  • Stan Stan on Aug 23, 2018

    The only problem I have with the vinegar and other natural solutions is that I’ve got to eradicate everything in a three acre vineyard and can’t afford the amount of vinegar it would take to kill the plants or the lime it would require to return my soil to neutral ph from acidic. Maybe ok for yard and garden purposes. Not practical for fields, orchards and vineyards.

  • Nancy Nardone Nancy Nardone on Apr 08, 2020

    don't use round up It causes cancer.


  • Mary Mary on Aug 16, 2020

    Never ingest Roundup.

  • Dorsetdrover Dorsetdrover on Sep 18, 2020

    I have an area of gravel at least 50m square plus a number of paths, also gravel.

    That rules out vinegar on cost, so I always use Roundup, however even that does not give a permanent solution as seeds constantly get blown in from nearby fields, so It is a battle I will never win but I have a desire to slow it down.

    I am not bothered if whatever I use makes the gravelled area sterile as I would see that as a bonus.

    For info I have no groundwater within 2km and no neighbours either and my garden has a 2m wall all round it on most sides. When I spray I am well aware of avoiding drift as we have things we don't want to kill.

    I can remember when we used Gramoxone which killed everything but was quite dangerous so it was withdrawn, so my question is, can anyone recommend any sort of weedkiller that actually works permanently?

  • Femmaeve MacQueen-Rose Femmaeve MacQueen-Rose on Jan 16, 2021

    The best time is NEVER. Those chemicals are carcinogenic.

    If the weeds are growing out from under stones or wood, try putting some weed cloth beneath to keep weeds from growing through.

    For weeds in the lawn, hand weed, don't let weeds go to seed, and don't disturb the soil unless absolutely necessary or else be prepared to weed. Let the grass grow a little higher to shade out weed seedlings. Harvest the dandelions for tea. Leave the clover so it can fix nitrogen and feed your lawn.

    If the weeds are growing in the cracks of a sidewalk, pour hot vinegar in the cracks once a season. For weeds in the garden or garden beds, mulch mulch mulch. Have fun!