I heard something about this idea from Canada, where many herbicides have been banned for use on lawns. I was surprised to find some results in my iron treatments to stimulate darker green in grass. Another member asked if it killed dandelions. I discovered that, true, the iron solution killed dandelions. At the very least, it caused their collapse and turned them black. I used 8 ounces of 15 percent iron as ferrous sulfate per quart, intending to cover about 1000 sqft with the quart.