What is a DIY good weed killer?

pour straight vinegar onto weeds in center/crown enuf to soak plant to get to roots do in full hot direct sun no rain for at least 3 days, do not add salt it will kill everything including soil & no grass will regrow; buy it by the gallon it's cheaper; then use preemergent on lawn to stop any new weeds from germinating; remove any weed seed heads before they disperse their seeds ;overseed lawn so grass chokes out weeds

yes...wetting & pulling is best but people are lazy. We tend to be comfortable with products we cook with and use in the kitchen. But it’s good to be cautious even with supposedly safe homemade remedies.

Boiling water really is organic. If you pour it piping hot on small weeds, it will likely kill them, and possibly harm whatever is growing around them. Many organic websites recommend it for killing small weeds that are growing in cracks in sidewalks or driveways.

Bigger weeds like dandelions that have taproots and are perennial may shrivel but they usually bounce back from such treatment.

Miracle cures?

The Dawn dish soap remedy pops up constantly as a miracle weed cure on Facebook pages devoted to gardening. There’s some logic behind the concoction. The dish soap helps the mix stick and spread on leaves. Salt can be toxic to plants. And vinegar has been used to fight weeds, though usually horticultural vinegar, which has about four times the acetic acid of the vinegar we use in the kitchen. At 20 percent acetic acid, horticultural vinegar is dangerous enough that users are supposed to wear long sleeves, gloves and goggles to protect themselves from burns and splashes.

The dish soap mix is a contact herbicide that works by drying out the leaves of the plant. Like Roundup, the mix doesn’t distinguish between good plants and bad plants, so if you decide to use it, watch where you spray it.

But like boiling water, this mix may kill only small weeds. Although results on bigger weeds look good at first when leaves show damage, perennial weeds and big weeds will likely bounce back. Roundup will take those weeds out, because it’s a systemic product that, unlike the soap mix, will kill the root of the weed.

There’s really nothing organic about the dish soap mix, either. All three main ingredients are chemicals, and one weed scientist who has written about it argues that toxicity levels in vinegar and salt may be higher than in glyphosate. (You can read his analysis here: weedcontrol-freaks.com/2014/06/salt-vinegar-and-glyphosate/)

The wild card in mixing your own “safe” weed killer is that people tend to get dangerously creative. I recently saw an online suggestion to add a cup of bleach to the dish soap mix, something that could not only create a toxic gas but that will permanently damage soil.

Lastly, the creeping Charlie question. The borax recipe came from research in Iowa and was embraced by homeowners because creeping Charlie is so hard to kill. While it’s still floating out there as an option, it’s no longer recommended by the University of Minnesota Extension. Borax, too, is a chemical. Use it more than twice to fight creeping Charlie, and it will kill your grass as well — lingering in the soil, and creating a dead zone where nothing else will grow.

So what’s a gardener who’s looking for organic solutions to do? There’s always good old muscle power, applied every couple of weeks aided by dandelion diggers and trowels. A stiff rake can remove a lot of creeping Charlie.

And there’s education. Magic solutions usually aren’t half as good as they sound, and sometimes they can do considerable harm. Do your research before you use any chemical — homemade or not — in the garden.