For years chemical weed killer has been a part of nearly everyone's lawn care routine. From pre-emergent crabgrass control, to weed-n-feed, to broadleaf weed killer, to advanced chemical herbicides that manage to kill everything but the lawn, to the ubiquitous RoundUp - killer of all plants. These harsh chemicals have become a way of life with entire neighborhoods smelling like 2,4-D after a visit by the lawn service. However, there is a green movement afoot. A growing number of people do not want to apply chemical pesticides to their lawn or contribute to their negative effect on the environment. In fact, pesticide laws and regulations are evolving to reflect the inherent dangers of chemical pesticides. So what is the responsible way to deal with lawn weeds?
An ounce of prevention
Organic weed control is not about treating weeds so much as it is about preventing them. A healthy soil leads to a healthy lawn which is not favorable to weed growth. Weeds are opportunists and usually an indication of an underlying problem. The presence of certain weeds can be signifiers of a deficiency in the soil or other issues which once solved will ease weed pressure. A thriving lawn is able outcompete weeds and avoid weed infestations. When weeds do make themselves present, it becomes about tolerance and maintaining a manageable threshold, then - if all else fails, treating the weeds with either an organic weed killer or removal by hand or other mechanical means. This philosophy is basically integrated pest management and when practiced, is an effective way to deal with pests.
There are more organic products on the market than ever and as demand increases, so does the effort to find organic alternatives to conventional weed control. Non-selective organic herbicides can contain such plant derived concentrates like clove oil and citric acid or acetic acid (vinegar). They are generally as effective as their chemical counterparts but are organically derived and far less hazardous to people, pets and the environment. There are no organic alternatives to weed-n-feed type products and other selective weed killers as of yet but organic science is progressing rapidly. Corn gluten meal can be used as a pre-emergent herbicide for springtime crabgrass prevention but is required in such large amounts that it is not cost effective or particularly good for the soil.
Sometimes the old ways are the best. A weed killing recipe could get handed down from generation to generation and make it possible to eradicate weeds without ever applying store bought chemicals. The most common home brew is some combination of vinegar, salt, and/or soap. Generally one gallon of vinegar, one cup of salt, and one tablespoon of soap. There are numerous variations on the recipe but the resulting concoction is usually a pretty good non-selective weed killer. The acetic acid of the vinegar goes to work disrupting the cells of the plant while the salt desiccates the tissue and the soap aids in sticking to the plant. It's effectiveness can be improved with stronger vinegar concentrations - most store bought vinegar is 5% acetic acid but concentrations of up to 20% can be found. Plants with hairs or waxy coatings may not be eradicated by the vinegar concoction ultimately making it not 100% effective.
Another popular home remedy is Ultra Dawn dish soap and water used as a moss killer. Simply mix 4 ounces of Ultra Dawn dish soap with 1 gallon of water in a sprayer and apply to the moss, it will turn brown and die in a week or so. Moss can be tricky to get rid of, generally the conditions causing it's presence need to be altered, but with an old recipe like dish soap and water it can be dealt with safely and cheaply.
Currently green weed killers are not quite as effective as their chemical based counterparts but organic science driven by consumer demand could bring new, more effective alternatives. The concept of green weed killers is kind of misleading anyway as organic weed control is a more holistic approach than just spraying your problems away. When the goal is a healthy soil, weeds tend to not be much of a concern as the soil biology is ramping up and providing ideal conditions for a lush, thriving lawn.