Soil settling

Soil settling is the ground sinking in over time. Where a stump was ground, wood and roots remain underground. As they rot, they shrink and leave gaps, and the soil above drops into them.

Purdue Extension says there will be significant settling of the ground below the stump as it decays and loses its structural fiber. It suggests adding soil to the stump area, with a little extra mounded up to make up for some decay.

Settling can leave a dip in the lawn months or years later. You can top it up with topsoil and reseed or lay sod. Lightly firming backfill as you place it helps too. See does the hole sink after stump grinding.