Can You Lay Sod Over Existing Grass?

Adding fresh grass to your lawn can be done by seed or sod, and both methods have their advantages. Sod consists of carpet-like rolls of grass that you attach to your land; the sod will dig its roots into the ground and create a new lawn. You can lay sod over grass that is already in place, but you must evaluate your lawn’s condition and needs before deciding to do so.

The biggest advantage of laying your sod over your old grass is that it cuts down on the amount of work that needs to be done to the lawn before sodding. If you decide to remove the grass, you will need to excavate the entire area over which you will lay the sod. You can also choose to till the old grass into the soil before laying new sod, but this also requires extra work -- and potentially extra money if you have to rent a soil tiller. Laying the sod over old grass also enables you to take advantage of the grass if it is growing healthily; some of the grass may grow up through the new sod to create a thicker look.

If you lay the sod directly over the grass, you will be adding an extra 2 to 3 inches of height to your yard. That may be OK if you are redoing an entire landscape, but to only cover a bare patch here and there, it will create bumps in your lawn. If your lawn is covered with weeds, the weeds can sprout through the new sod and create the same problems you were having before. Also, your sod will have to push down through the layer of existing grass before it can reach the soil; laying it over the old grass will delay the establishment of new roots and, in some cases, may cause the sod to dry out before it has a chance to attach.

If you have the time, money or labor to spare, you will be better off removing the old grass. Excavate the area where you will lay the sod to accommodate the thickness of the sod. For example, if your sod is 2 inches thick, dig out 2 inches of grass and soil from the area to create a smooth, flat surface. When the grass is removed, till the soil to a depth of about 10 inches, fertilize the area with a high-phosphorous fertilizer and water the soil to make it moist. The food and water in the soil will encourage the sod’s roots to grow down quickly.

Fill in any gaps between sod pieces with some of the soil you removed or with fresh planting soil. Never use soil that contained any kind of fungus or disease from other plants. Roll over the new sod with a lawn roller half filled with water to create a firm connection between the sod and the soil below. Water the sod to a depth of 6 to 8 inches every day for at least six weeks to encourage the roots to spread out. You will be able to fertilize and mow the new sod within seven weeks of planting.