You are looking for 9% to 15% vinegar that is sold in some nurseries that carry organic gardening supplies. Sometimes it's referred to as agricultural vinegar. You probably won't find it at a chain store. Grocery stores usually don't have it. I've used 5% vinegar on tiny weeds. It works on those but I've had no luck using it on established plants. I'm not super fussy about weeds. The only thing I take after with a vengeance is stray Bermuda grass.
It should tell you the concentration of acid in the vinegar on the bottle. My regular white vinegar is 5% and the balsamic is 6%. I think 5% is standard for white vinegar.
I live in Texas and HEB grocery carries both 5 and 9% in gallon size. I would imagine any grocerer could special order the 9% if you make a request. But I agree with other posters, the 5% will probably work fine.
Five percent has always worked for me to kill weeds. I use it around my veggie garden to keep the weeds from growing into the fence. I have to fence it or the rabbits chew everything off.
The 4 or 5 % vinegar sold in gallons at the grocers does work. Give it a chance and perhaps a second hit, maybe even a third hit. Do not dilute. Sometimes up to a week of waiting. It even killed my bamboo because i was persistent. Bamboo was cut short and i soaked the roots. I have killed thistle, dandelions and other pesty weeds. Few years ago i knew no different and used Roundup. I have no more tree frogs, just bugs. Several of my dogs got cancer. Not sure the cancer was caused by the roundup but it is not healthy for them or me. Never again.
The dark colored vinegar is stronger than the white which is stabilized at 5% but if you put vinegar full strength to kill weeds you will also kill the trees roots that go under it. be careful with vinegar.
I have no idea if it would work or not, but could you simmer some vinegar to reduce the volume, thereby increasing its concentration?
With canning time coming up check the concentration of the vinegars. Some are sold as vinegar and some as Pickling Vinegar which is usually higher in acetic acid.
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