Lawn needs major help
When we moved into our new home 12 years ago, the builder had not planted any grass in the back yard - there was muddy red clay between scattered ugly weeds. (Had been farmland prior.) We spread mushroom soil everywhere (~4" thick) and planted turf-type fescue seed. That part of the lawn has been so fantastic that weeds can't even get a foothold among the healthy blades of grass! However, we didn't do anything to the back half of the back yard, since there was enough vegetation there to cover up the mud. Since then we have tried several times to improve that part of the yard, which is 90-95% weeds. We even had it all sprayed with Roundup, topsoil brought in, and re-seeded. Still >90% weeds (all kinds). Wondering if we can just cover back there with mushroom soil and plant seed in that, like we did before. Questions: how deep would the mushroom soil have to be to smother/kill the existing weeds? Or would that idea not even work, since the weed seeds would be down there in the soil? If it could potentially work, should we apply lime and fertilizer to the existing soil first, according to soil test recommendations? Or just let that go, since we'd be putting down a new top layer? P.S. We are just 1/2 mile over the MD line!
Chester County Pennsylvania lawn
The following link discusses lawn renovation. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG102%20Lawn%20Estab... It is possible that the top soil that you brought in had weed seeds in it. You might consider hitting the area to be renovated with glyphosate and then putting down mushroom soil. If you put down a couple of inches you will not have to put down fertilizer and lime. There are some weeds that might be vigorous enough to come up through four inches of mushroom soil if you do not hit them with glyphosate first. http://plantscience.psu.edu/research/centers/turf/extension/factsheets/mushroom-soil vw