Vinegar for weed control

albabyDecember 5, 2012

First time posting in a while - still a relatively novice vegetable gardener down here in Miami, growing some selected veggies in a few raised bed gardens. And I've got a bit of a weed problem.

Not in the beds, which are pretty well mulched with hay - but in the mulch path between the beds. I guess enough weed seeds are getting blown into the mulch that they're rooting in the mulch itself (there's landscape fabric underneath). I pull 'em out by hand now, but it's a bit annoying to do that frequently.

A friend suggested zapping them with vinegar (with a small amount of soap added) - that will fry the weeds, and shouldn't get into the raised beds adjacent to them. Still, I'm finally starting to get some positive results out of my garden (except the tomatoes, blast them), and I don't want to fry my other veggies. Any thoughts on whether it's a good idea to try this?

Alan

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writersblock

It won't hurt anything, but it won't make a difference, either, most likely. I once tried to get the weeds that come up between the pavers on my patio with a mix of full strength vinegar and salt. They loved it.

    Bookmark   December 5, 2012 at 1:09PM
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bamboo_rabbit(9A Inverness FL)

Horticultural vinegar is deadly to weeds and even more deadly than roundup on some weeds. It is a much stronger concentration of acid than what you would have in your kitchen.

    Bookmark   December 5, 2012 at 6:04PM
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writersblock

Where would you get that, bamboo_rabbit? The household kind sure doesn't do anything.

    Bookmark   December 5, 2012 at 10:54PM
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bamboo_rabbit(9A Inverness FL)

You can get the horticultural vinegar online, Amazon..lots of places. You can also make your own by concentrating vinegar by freezing normal vinegar to lock up the water. Normal vinegar is about 5% you need 10% or higher. Roundup is easier but it isn't organic (rolls eyes) so some people want a natural solution.

    Bookmark   December 6, 2012 at 9:07AM
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writersblock

Thanks!

    Bookmark   December 6, 2012 at 9:25AM
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tomncath(St Pete Z10a Heat 10)

Normal vinegar is about 5% you need 10% or higher. Roundup is easier but it isn't organic (rolls eyes) so some people want a natural solution.

No rolling eyes here, caught my interest...gotta check this out BR. Thanks!

Tom

    Bookmark   December 6, 2012 at 7:07PM
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bamboo_rabbit(9A Inverness FL)

Your'e welcome Tom. I heard about and bought a "red weeder" recently and they had an article on their website about the vinegar.

    Bookmark   December 6, 2012 at 7:23PM
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writersblock

That red weeder looks really interesting. How do you like it?

    Bookmark   December 6, 2012 at 7:29PM
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bamboo_rabbit(9A Inverness FL)

I love it and you use probably 1/10th the amount of weedkiller with it.

    Bookmark   December 6, 2012 at 9:28PM
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albaby

Thanks for the comments, everyone. I'll concentrate up some of the household vinegar, and give it a go. I've been reluctant to use Round-up for fear of somehow damaging the actual veggie beds, which is why I was leaning towards the vinegar.

Alan

    Bookmark   December 6, 2012 at 9:59PM
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writersblock

Thanks again, BR.

    Bookmark   December 6, 2012 at 11:58PM
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tomncath(St Pete Z10a Heat 10)

I'd really like to try the 20% stuff but sure hate to pay for shipping. I called Shells Feed store in Tampa and Neeld-Gordon in St. Pete and they both acted like I was speaking in a foreign language, apparently this application is not well known.

Tom

    Bookmark   December 8, 2012 at 10:14AM
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albaby

Reporting my experience with the vinegar - success!

Taking up the comments above, I didn't just apply the ordinary household vinegar directly. Instead, I concentrated the acetic acid up to close to 20%. I simply took the vinegar and froze it solid, and then allowed it to melt until about a quarter of the volume had melted. Since acetic acid has a lower freezing point than water, the resulting mixture was far more concentrated than the original vinegar (and hopefully something along the order of 20%).

I applied to the weeds, and within about an hour and a half in the sun they were withered and brown - even the really established ones. I'm concentrated up another batch right now for use on the driveway pavers!

Alan

    Bookmark   December 9, 2012 at 2:32PM
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tomncath(St Pete Z10a Heat 10)

Thanks Alan, I'll give that a try. Cheapest I could find for the 20% was about $17 a gallon, including shipping, but that was for four gallons. :-(

Tom

    Bookmark   December 9, 2012 at 4:19PM
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tomncath(St Pete Z10a Heat 10)

Alan,

I hate to break this to you but I just ran the figures and best case scenario you boosted your acetic acid up to 6.6%.

5% acetic acid = 5gm/100ml
1 gallon = 3785ml
37.85 x 5gm = 189gm
3785ml x 75% vol. = 2839ml
189gm/2839ml = 6.6%

Still, if it worked it's worth a try....

Tom

This post was edited by tomncath on Mon, Dec 10, 12 at 7:33

    Bookmark   December 10, 2012 at 7:21AM
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albaby

Tom, I just wasn't very clear in my description. I let a quarter melt off by volume...and that's the part I keep, while tossing the ice that remains. The acetic acid melts first, so what's still frozen in the bottle is mostly ice - while the liquid contains almost all the acid. I end up with 1/4 the volume that I started with, but it should have most of the acid in it.

So you have:
3785ml x 25% vol. = 946 ml
189 gm/946 ml = 20%

Of course, I'm just doing this in the bottle in my home freezer and measuring by eye - but by reducing the volume out by 75%, I should be getting somewhere in that vicinity.

Alan

    Bookmark   December 10, 2012 at 7:47AM
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shuffles_gw

I am wondering if citric acid wouldn't work just as well? It is widely available. I think I'll give it a try. Tom, how much by weight in a quart of water would yield a 20% solution?

    Bookmark   December 10, 2012 at 7:52AM
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tomncath(St Pete Z10a Heat 10)

Tom, I just wasn't very clear in my description....

Cool Alan! I didn't look at the melting point of acetic acid, it's 60.8F. Much higher than water so you are right ;-) The next question is, is a gallon of 5% vinegar less 75% volume less than $17/4 = $4.25 for 1000ml of the concentrate? Probably, yes :-)

I am wondering if citric acid wouldn't work just as well?

Hi T, I'll crunch the numbers if you can give me the percentage of your citric acid? With a melting point of 307F it's obviously liquid and only needs to be diluted MAYBE, 20%? Perhaps we can come up with an environmentally safe acid-substitute weed killer but wouldn't you think some brainiacs out there have thought of this before us?

Tom

This post was edited by tomncath on Tue, Dec 11, 12 at 7:31

    Bookmark   December 10, 2012 at 7:00PM
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bamboo_rabbit(9A Inverness FL)

The problem with the acid as opposed to say roundup is that the acid only burns off the plant tops. Those weeds that can come back from the roots will which will require re-treatment.

    Bookmark   December 10, 2012 at 7:37PM
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L_in_FL(8B/9A Border, NW FL)

Probably a liability thing.

Case 1: Consumer splashes Roundup in his eyes, he rinses his eyes and they maybe sting a little from the soapy sticking agent. Or consumer sprays in windy conditions and gets droplets all over his skin. He doesn't experience any irritation.

Case 2: Consumer splashes strong acetic acid in his eyes, and suffers an eye injury. Or, consumer sprays in windy conditions and gets droplets all over his skin, and ends up red and blistered a few hours later. Lawsuit ensues.

So I figure if companies were going to distribute acids for weed killing, they'd probably dilute them to the point of uselessness anyway.

By the way, acetic acid is not that dangerous up to about 20% concentration, but it is strong enough to cause real damage (not just irritation) if you get over 25% concentration. Please be careful with your home concentrating. Citric acid is probably safer to handle, but I have no idea if it would be effective as a weed killer.

    Bookmark   December 10, 2012 at 7:44PM
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shuffles_gw

Tom, citric acid is sold as a crystalline powder that I think is close to 100% pure citric acic. I have a few pounds in a plastic bag. Would 12 ounces by weight in a quart of water be close to a 20% solution?

    Bookmark   December 11, 2012 at 7:22AM
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tomncath(St Pete Z10a Heat 10)

...but it is strong enough to cause real damage (not just irritation) if you get over 25% concentration....

True, I know someone who spilled glacial acetic acid (anhydrous - 89%) on his hands and the result was that his skin continuously sloughed off for over a decade. Caution is advised.

BR - thanks for the info, I'd still like to try it in my veggie garden vs. Roundup.

Alan - we need to push the envelope with this little experiment to see where the breakpoint is for time/money savings. I'm going to save 1/3 of a gallon (189/1260 = 15%), add an ounce of Simple Green to it as a surfactant and see what happens. I'll post before and after pictures and you should too.

Tom

This post was edited by tomncath on Tue, Dec 11, 12 at 7:50

    Bookmark   December 11, 2012 at 7:28AM
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tomncath(St Pete Z10a Heat 10)

...citric acid is sold as a crystalline powder that I think is close to 100% pure citric acic...Would 12 ounces by weight in a quart of water be close to a 20% solution?

Hi T, looks like we were posting at the same time. If it is anhydrous (100%), to get a 20% concentration you'd need 200grams per 1000ml (approximately a quart). In ounces that equates to approximately 7 ounces per liter/quart.

Tom

    Bookmark   December 11, 2012 at 7:46AM
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albaby

Tom,

Will do (though I have a very modest garden, so I don't really need to produce too much of this stuff). I'm also going to take L's caution well to heart - I'm going to start being a bit more precise in my measurements and make sure that I err towards a weaker acid. I'd rather have to reapply - or even have weeds - than injury.

Alan

    Bookmark   December 11, 2012 at 8:02AM
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tomncath(St Pete Z10a Heat 10)

I put a gallon of vinegar in the freezer last Saturday at 8:00 P.M. and was surprised when I removed it Sunday at 10:00 A.M., it was not totally frozen after 14 hours! I drained off 1500ml so IF I captured most of the acetic acid that would be 12.6% solution (189gm/1500ml). We expected rain early this week which didn't materialize, and now we're expecting rain tomorrow so I can't proceed with this experiment as spraying the plants shortly before rain would most likely not be an optimal outcome....Details to follow when I can do this right.

Tom

    Bookmark   December 20, 2012 at 7:41PM
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albaby

Tom,

Were you ever able to implement your test application? I'm curious how it worked for you. I had great results with spraying here, and I haven't had to reapply - so I don't have before and after pics yet.

Alan

    Bookmark   January 1, 2013 at 10:11AM
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tomncath(St Pete Z10a Heat 10)

No, other things going on....I wanted to try this weekend but looks like rain on and off since Thursday :-( I will report back to this post though as I intend to clip it if my results are positive.

Tom

    Bookmark   January 4, 2013 at 7:01PM
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