Lawns can be managed organically and many weed problems eliminated through cultural practices. Management practices that affect weed growth include mowing at 2 ½ to 3 inches, fertilizing more heavily in the autumn, frequent shallow irrigation, reseeding thinned lawn areas and using nonchemical weed treatments. Some weed species are desirable because they provide nutrients to soil.
Organic Soil Care
Soil is improved organically by using fertilizers derived from natural sources such as animal manures, fish waste and seaweeds. Natural fertilizers are available at garden centers. Backyard compost is a beneficial lawn soil amendment that is easily made from kitchen scraps and garden clippings. Compost is sieved to create a fine-textured lawn improvement amendment.
Traditional weed killer is toxic to pet and human health. Traditional chemical fertilizers deteriorate soil fertility by disrupting its natural biological functioning. Organic fertilizers are applied less frequently but the timing is important. Apply spring and fall for a constant cycle of release of nutrients. Improved soil supports healthy plants that are able to resist disease and harmful insect infestation.
"Lawn grass grown on healthy topsoil and managed organically has fewer weed problems," according to an Ohio State University Extension report on organic lawn care. Clover left to grow in the lawn is beneficial because it holds nitrogen in the soil; nitrogen is the most essential nutrient for plant growth. Dandelions are kept under control by cutting out the root in early spring after they have leafed out.
Corn Gluten Herbicide
Corn gluten is a pre-emergent herbicide that is effective against crabgrass, foxtails, barnyardgrass, dandelion, lambsquarter, pigweed, purslane and smartweed. Corn gluten herbicide is a corn syrup by-product that also contains growth-producing nitrogen. Its effect is cumulative because it progressively eliminates weed seeds. Apply corn gluten after the last spring frost and again in autumn.
Herbicidal soaps are fatty-acid-based nonselective herbicides. They penetrate plant tissue and disrupt cellular structure. The weed eventually dehydrates and dies. Herbicidal soap is effective against small annual and biannual weeds such as chickweed, spotted spurge and crabgrass. It is less effective on perennial weeds and plants with a large taproot such as thistle. It is effective only on direct contact with the plant.