I ripped out some bushes last fall and reseeded the area. The grass came in ok but the area where I took out the bushes, tilled the soil and reseeded sunk lower than the existing grass. So now I have a ridge in my lawn where the new grass meets the old grass that you can feel when walking and it's quite noticeable. I was wondering if I can just lay topsoil over the existing grass in the lower area to bring up the level and reseed or do I have to take up the grass first then lay new topsoil? Thanks.
Put down topsoil and reseed. Make sure to walk on the topsoil to compact/level it first. Then loosen up with pitchfork, seed/starter fert/lime. You can use existing sod in any bare areas you have or throw in the compost bin.