Weeds can detract from the elegance of a well-manicured lawn. Poorly maintained lawns are prone to weed infestations. Weeds typically have deeper penetrating roots than grass does. This allows them access to a consistent water supply during drier months of the year. As the grass becomes water-stressed, the weeds are able to slowly take over and keep spreading throughout the lawn. By keeping the grass healthy, you can keep the weeds in check. Herbicide also works for knocking weeds back when they get out of control.
Mow your grass at the recommended cutting height. For cool-season grasses like ryegrass, Kentucky bluegrass and fescues, mow at a height of 2 1/2 to 3 1/2 inches. Mow every 5 to 7 days to prevent removing more than one-third of the grass blade in a single mowing. Tall grass will shade out the weeds and help form a thick, lush turf.
Fertilize your lawn with 3 to 4 lbs of nitrogen per 1000 square feet each year over three to four applications. Use a broadcast spreader to spread the fertilizer, and follow the instructions on the fertilizer bag. Applications should be in late May, late June, late August (optional) and early October.
Water your lawn so that it receives at least 1 inch of water per week during the growing season. Set a pan out in your lawn, and run the sprinklers to see how long it takes to fill the pan with 1 inch of water. This is how long you need to run the sprinklers each week to provide the necessary water to your lawn.
Spray your lawn with a herbicide that contains the chemical 2,4-D. Spray the entire lawn until all the grass blades and weeds are covered. Repeat the process in two weeks if the weeds didn't sufficiently die.
Provide more light to areas that are in heavy shade. Prune off and thin out tree limbs to allow more sunlight to reach the ground. Grass does not like growing in heavy shade, but moss and some weeds do. By changing the lighting conditions, you'll enable the grass to get an upper hand over the weeds and moss.
Mulch areas where you can't increase the amount of light with a 2-to-3-inch layer of wood mulch. The mulch will prevent weeds from growing and make the area look less unsightly.