How to Prepare Subgrade to Install Grass Sod

Testing and Tilling

• 1

  Test the pH level of the subgrade soil to determine what kind of fertilizer you need. A test lets you know the nutrient content of the soil and whether it is acidic, neutral or basic. Send samples to the nearest extension office for analysis or test the soil yourself with an at-home kit.

• 2

  Break up the soil with a rototiller. Make sure the blades are set to 8 inches deep. An initial pass with the rototiller loosens up debris and enables fertilizer to spread more evenly.

• 3

  Remove any debris that could potentially interfere with the establishment of the sod's root system. Pick out stones, twigs and weeds.

Measure the Slope

• 4

  Tie a string to a stake then place the stake at the base of your house. Make sure the string is at ground level.

• 5

  Pull the string 50 feet away from the base. Pull the string taut. Tie it to another stake and tamp the stake into the subgrade soil.

• 6

  Make the string level. Set a carpenter's rule on the string. Raise or lower the stake until you can see the bubble in the brackets of the carpenter's level.

• 7

  Measure the distance between the ground and the spot where the string attaches to the stake. If the drop is more than 3 inches, the slope is sufficient. If the drop is less than 3 inches, you need to regrade.

Establish the Rough Grade

• 8

  Use a shovel and wheelbarrow to move soil from high spots to low spots. You may have to add 4 to 6 inches of topsoil to create a uniform surface.

• 9

  Level the soil. Use a landscaper's rake to break up the remaining dirt clods. Then use the rake's flat edge to smooth out the surface.

• 10

  Install drainage pipes or ditches as necessary. Both pipes and ditches divert water away from wet areas to other areas that absorb water better.

• 11

  Apply fertilizer and amendments (materials that improve soil conditions) as recommended by the soil test. For example, if the soil test indicates the soil has phosphorus and potassium deficiencies, spread a 10-10-10 fertilizer, or a product with equal portions of nitrogen, phosphorus and potassium. Add lime to raise the pH or sulfur to lower the pH. Allow the fertilizer and amendments to settle into the subgrade soil for a week before you prepare the finish grade and install grass sod.