I can’t tell you how often I am asked (or hear others ask) what works for weeds. This is a tough question to answer. What do you mean by “works”?
If you are meaning what will make them go away and never come back, the answer is nothing. Even in Carthage, where the Romans salted the earth so many centuries ago to obliterate any chance of culture forming there again, there is now fertile earth that supports, amongst many plant life, weeds.
But perhaps you mean just for your lifetime, or even just a year? Salting the earth might work for your lifetime, but for just a year, I’d say nothing “works”. Nothing organic, nothing that they sell at the hardware store or garden center, nothing will get them all for very long. Chemicals break down, and anything legal today is designed to break down fairly quickly to minimize it’s risk of getting into our water or doing long term damage to the soil (note: it still does those things, just to a lesser degree than, say, DDT). So if you spray something, it might kill the plants, but there may be seeds still in your yard that will outlast the chemical you sprayed, and will sprout and grow. Or new seeds will be blown in, or carried in by birds, mice, squirrels, etc.
Honestly, though, I’m skeptical that most chemical solutions, whether store bought (like RoundUp) or home made (like the dish soap and vinegar concoction everyone seems so fond of online) actually kill weeds. Having used them a few times in my life, I’m pretty sure all they do is wilt the leaves. So before long, they spring back, along with all those seeds in mentioned above. Meanwhile, we’re getting harmful chemicals into our water and air through spraying, and we’re killing off the micro biome in the soil that allows plants to get nutrients from the soil (which eventually end up in us and other animals that eat those plants), decompose dead things, and support any kind of life that hasn’t specifically evolved to thrive in sterile soil (in other words, weeds). The eventual outcome of spraying, yes, even vinegar, is the creation of soil in which only weeds can grow, and if the weeds have no competition for space from other plants, they will grow, aggressively. At that point, though, it’s probably good that the weeds grow. They’re the only thing that will bring life back to the dead soil.
Given this experience, and my knowledge of what these chemicals do to our water and the soil microbiome, my preferred methods of weeding are digging and torching. Digging is the most effective. When you get the majority of a root up out of the ground, you know that weed is dead and gone forever. Yes, it may have left seeds, but it won’t survive to make any more. If you don’t get the whole root, there’s still a chance that weed is dead, and even if it grows back, you’ve seriously stunted it’s ability to make seeds, meaning it might reproduce less this season than it would have had you not dug it.
Torching works much like spraying, but is way less toxic. And it’s kind of fun. I don’t think it gets the root very well in most cases, but it’s no worse than sprays, and way better for our soil and water.
I am not sentimental about weeds. You won’t hear me describing dandelions as wildflowers, or keeping lambs ear growing because it can be medicinal. I learned my lesson about letting purslane have a place in my garden, and I advise people to pull anything they don’t recognize in their garden. But I also have taken a realistic viewpoint on weeds, and stopped looking for some magic fix for them. Weeds will always be there, always keep coming, and I have to accept and make peace with the fact that I will always need to meet them to do battle against them in my yard. This is the nature of life, and frankly I would be scared and worried if something stopped their constant assault. The loss of weeds, plants that evolved with civilization to thrive in the destruction we reap upon all other life, would be a pretty big dead canary in our metaphorical coal mine. Weeds are our promise that life can find a way in even the most dismal conditions, and to find a way to squelch that permanently would spell certain doom for more delicate creatures, like ourselves.