Planting Grass Over Ground-Stumps

There are many stumps that were backfilled with a mix of chain saw chips and the old dirt, mainly the first, after being ground down below surface. The areas vary from 1/2 foot to almost 2 ft across for the mature trees that were removed.

Should there be a wait time before planting grass? I've head the new wood can change the PH of the soil. Some have told me 'waiting' can take 2 years til something grows.

Sod vs seed - same argument as always? Though whatever it is will have to settle ...

Our lawn treatment company said to just let the areas age, maybe plant in the spring. The spots are spongey when stepped on.

You will have the spongy problem until the chips start to decompose & compact. Wet the area down, not soggy, run a whacker over it, add some top soil and seed or sod. Gradually a low spot will develope.

How big is the area and how deep is the soil mix?

Wood chips will lower the soil ph and make it more acidic but that doesnt necessarily mean the soil ph is off. Maybe the soil ph was high to begin with. You definitely don't need to wait 2 years to grow there. Lime can be added to adjust ph levels upward if necessary. The only way to tell is do a soil test. A ph of 6.0-7.0 is optimum and 5.5-7.5 is acceptable. PH levels mainly affect a plants ability to absorb nutrients.

Filling an area with wood chips is like trying to fill with compost. The stuff eventually breaks down and you have a depression. If you just want to get grass to grow, plant a TTTF/KBG mix @ 90/10. The TTTF will establish pretty fast and the KBG will spread and fill in areas later on. This is a common mix for cool-season grasses. Whether it makes it through summer heat is another issue due to the way you filled the stump areas. Your roots will always be succeptable to heat or cold and probably drought damage if too much sawdust was used.

Also, it's almost too late in the season to plant seed. The roots might not be developed enough by winter. Wait until early spring and use starter fert. high in phosphorus (2nd number on bag) for good root development.

Why not just dig 4" out and fill with top soil.

Which is what I've been considering. Tamp it down and place sod.

Or you can do what I did. Took out a dead silver maple, ground the stump and planted a new sweet gum. Planted it high cause I knew the area was going to sink.

3 years later I got a nice sweet gum in a mound in the center of a depression. I keep telling myself I am going to bring home a PU load of topsoil and fill it in, but haven't so far. Can't even mow around it with the zero turn cause it scalps the high spots around the edges. Have to get out the push mower.

Lazy I reckon.

Just plant some 'shrooms there... Seems like they always pop up over old stumps

Yes, the wood chips (down in the soil, not on top, like mulch is used) will rob the area of nitrogen and cause a manganese build-up in the soil. But it will also be as suggested that the wood will decompose over time, thus sink. If you are able, and the area has need of blending in soon as a nice, lush lawn, you will need to pull out as much of the organic material as possible and fill in with suitable soils that match the surrounding soil's ph level. Then, depending upon what area of the county you're in, you can then either sow seed (fall for fescue, early summer for Bermuda, or other warm weather grasses) with a starter fertilizer, or you can by sod to match what you have in the yard. I prefer sowing seed and working the seed in to get good soil contact and watering it properly for the first several weeks, depending on the species.