Weeds in your lawn compete with grass for nutrients and water. As a result of their aggressive nature, the weeds usually win, making the best option starting over from bare soil. While spreading grass seed is the most inexpensive way to start new grass, laying sod strips proves the better option because invasive weeds can choke out grass seedlings before they have a chance to establish a healthy lawn. Sod grass is already well established in its thin layer of soil and can smother any weed seeds that might germinate.
Push a sharp spade straight down in the soil to cut through the weed roots and into the soil below. Cut about 12 inches outside the perimeter of the weed patch to ensure you remove all of the problem weeds. Pull the weeds and the root layer out of the ground, leaving only bare soil. If desired, use the spade to cut the weed patch into several narrow strips so you can roll the weeds and roots up like you would roll a carpet.
Loosen the soil to a depth of about 8 inches, using a rototiller or hand digging tools such as a shovel, mattock and hoe. Pick out any root or plant pieces as you dig through the soil; some weeds can resprout from even the smallest root piece.
Spread the soil evenly, using the back side of a bow rake, creating an even surface for laying the sod strips. Water the soil just enough to prevent dust as you install the sod.
Lay the first piece of sod along one side of the bare soil. Sod often comes in squares or rectangles that you piece together like a puzzle, but it might come in rolls that you unroll across the soil. Use a sharp masonry trowel or carpet knife to cut sod strips into smaller, more manageable pieces. Sod also requires cutting to fit irregular spaces or when a small piece is needed at the ends of the rows. Butt separate pieces close together so there are no gaps.
Lay a second row of sod directly against the first row, with the joints of separate pieces staggered with the joints of the previous row. The joint where two pieces of sod meet should be at the center of a sod piece in the second row. Continue laying rows of sod until you fill in the entire area. Place a piece of plywood on the new sod and kneel on it as you work your way to the other side so you don't crush the sod.
Roll a lawn roller over the sod immediately to press the roots down into the soil below and push out air pockets.
Water the new sod deeply so water drains through the turf and into the soil below. Water the sod frequently to keep the grass moist, but not wet, for about two weeks until the roots establish in the soil below.