You can learn a lot on the Internet. Here’s some of the garden wisdom I’ve gleaned lately on how to control pesky weeds with supposedly organic solutions:
• To kill weeds, use a mix of Dawn dish soap, Epsom salts and vinegar.
• Boiling water will kill weeds.
• To get rid of creeping Charlie, use borax (as in 20-Mule Team Borax) instead of conventional lawn chemicals.
All of these remedies are pitched as safe alternatives to chemicals like Roundup, the glyphosate-based chemical that kills anything green. But are they really safer?
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.
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.
Mary Jane Smetanka is a Master Gardener and Minneapolis freelance writer.