The Perfect Earth Project’s Edwin von Gal and Sean O’Neill, a former pesticide control specialist for the New York State Department of Environmental Conservation, recommend the following five steps for maintaining a healthy lawn without chemicals:
Healthy soil provides a sort of natural immune system for the lawn, keeping it naturally resistant to pests and disease. Keep the soil rich in organic matter.
Replace frequent watering with infrequent, deep watering as needed to produce deeply rooted, disease-resistant turf. Overwatering creates its own problems that end up being treated with chemicals, as well as attracting mosquitoes and making lawns mushy.
Leave grass longer to promote photosynthesis and healthier, deeper roots, as well as to naturally shade out weeds. Mow with a sharp blade at 3 to 4 inches—and more frequently in spring, less frequently in summer. Use a mulching mower and leave clippings to return nutrients to the soil.
Fertilize in the fall with slow-acting compost. Grasses are cool-season plants. Fertilizing in spring pushes them to grow greener more quickly and leaves it weaker and more vulnerable to fungus and insect infestations that often are treated with pesticides and fungicides, which in turn can kill helpful living things, like nematodes that control grubs.
Rake and over-seed in fall when weed seeds are dormant and grass seeds are most viable. The fall-germinated grass will fill bare spots and make it more difficult for weeds to find a footing in the spring, in turn making herbicides unnecessary.