The best way to keep your lawn free of weeds is to fertilize, water, and mow it properly. You can also make your lawn more resilient to weeds (and drought) by allowing it to grow longer. A healthy lawn will resist weeds without your having to apply chemical herbicides.
But if you're going to use herbicides to deal with broadleaf plantain, crabgrass, dandelions (shown), oxalis, and countless other weeds, you'll need to apply it properly. To identify common lawn weeds, use our interactive guide. Keep in mind that spot application of herbicides will require the use of less chemicals, which could save you money and be better for the environment.
Herbicides are classified according to their use or mode of action:
Nonselective herbicides like Roundup kill all kinds of plants.
Selective herbicides like Ortho Weed-B-Gon Max Weed Killer for Lawns Concentrate kill some plants but not others. In your lawn, selective herbicides kill dicots (which include many common lawn weeds), plants with branching veins in variously shaped leaves.
Postemergent herbicides such as Roundup and Weed-B-Gon kill growing weeds and may be either selective or not.
Preemergent herbicides prevent some weed seeds from even germinating. They are typically used in early spring to prevent crabgrass. Most often these herbicides are combined with a fertilizer, as in Scotts Turf Builder Halts Crabgrass Preventer.
To learn how to safely and properly use granular herbicides and concentrated liquid sprays, read our expert advice.