If you only put a thin layer of soil down, the old weeds and grass will through your soil. ... (Grass and weeds will grow through soil 2 or 3 inches thick quite easily.) Once you add more than 3 or 4 inches of soil, the amount of weeds and grass that will grow through starts to drop off dramatically.

Will grass grow in just topsoil?

Grass only puts down shallow roots in a thin a layer of topsoil, which can result in sparse growth and nutrient deficiencies. ... Grass roots grow between 4 and 6 inches long, so a layer of topsoil that's 6 inches deep provides enough room for the roots to grow.

How long does it take for grass to grow from topsoil?

Seeing too much or too little of the seeds can indicate that the soil is not aerated enough or that it has been aerated too deeply. It typically takes about three weeks for grass seeds to sprout.