Weed control seems to be the biggest reason that people use chemicals in their yards and herbicides certainly are needed to combat poison ivy or certain invasives like Japanese Knot Weed. I've never had a patio made from pavers before, and when all sorts of weeds came up between the cracks this spring, I decided to try a very simple organic solution to kill them. . . vinegar! The first article I read about it suggested a solution of 1 cup vinegar to 16 oz of water which is what I used in the above dandelion experiment. The pictures show the dandelion prior to spraying and then 2 days later. I had planned on taking another pic in two more days but the weed was basically gone! I also tried using the solution on some dandelions in the lawn but it did brown the grass. The dandelion grew back and I have resprayed, this time using 100% vinegar. Each time you attack a weed it will regrow weaker and eventually die. The really nice thing about the vinegar is that I don't have to wear protective clothes so I tend to do it more often. I've also read that you can use boiling water. Oh, the vinegar does not seem to affect garlic mustard, the bane of my existence right now.
Combatting weeds in the lawn requires a long-term strategy: a top dressing of compost starts microbial action in the soil, mowing your grass at the highest possible setting shades the soil which helps keep it moist and discourages weed seed germination, letting your grass clippings remain on the lawn actually serves as fertilizer because those microbes break them down and produce nitrogen, spreading corn gluten meal also inhibits weed germination and is another source of nitrogen, and watering infrequently but deeply promotes deep root growth and a thicker lawn. More in depth information provided by the ML Environmental Commission can be found here. I've been using organic methods at my previous homes for over 15 years. My experience is that your yard won't have an overnight transformation--it'll take about three years until your lawn can fight weeds and insects on its own, but your family, pets and our environment will be healthier for your effort.
