Here is the vinegar weed killer we’ve been experimenting with.
It appears to do a good job of killing the plant, but if it is particularly mature, and thus has a long and robust tap root, then looks are deceiving: a new stem and flower will eventually grow out from among the dead leaves. In these cases you’ll need to spray again — and of course eventually you’ll want to dig out all those carcasses.
We don’t yet know if it will be successful in the long term, but here is the recipe we’re trying:
- 1 gallon of 8% to 10% vinegar
- 1/4 cup salt
- 1 tablespoon Dawn dishwashing liquid
A common ratio promoted on internet forums is one gallon of household (5%) vinegar plus one cup of salt plus one tablespoon of dish soap. But that’s a lot of salt. The vinegar and dish soap should biodegrade in a few days with minimal lasting impact to the soil, but the salt will remain, so I’ve been using a higher concentration of vinegar and less salt.
There’s some controversy whether any salt is needed at all, but the majority opinion online is that it makes a more effective solution. I hope that for surgical spot treatment, a bit of salt here and there won’t damage the soil much. I imagine that our septic leach lines emit a greater quantity of salt from our water-softened tap water.
The vinegar and salt are intended to desiccate the plant and disrupt its biology. The dish soap is a surfactant to help the solution adhere to the plant and cut through oily or waxy cellular walls. We get jugs of 30% vinegar from Rick’s Hardware and dilute it.
There are disadvantages to this DIY formula. It’s non-selective and kills anything it contacts above the soil. It seems to permanently kill young, shallow plants, but it might require multiple treatments before deep dandelion roots loose their motivation to resprout.
The weed battles have just begun. I haven’t ruled out hiring a crop duster.
References:
Pro: USDA, “Spray Weeds With Vinegar?,” https://www.ars.usda.gov/news-events/news/research-news/2002/spray-weeds-with-vinegar/
Con: LawnStarter, “Vinegar as a Weed Killer: You’re Probably Doing It Wrong.” https://www.lawnstarter.com/blog/lawn-care-2/vinegar-as-a-weed-killer-youre-probably-doing-it-wrong/