Does using a mulching mower kill your lawn?

If you have the height set to low it can cause the lawn to brown up. Lack of water will do the same, as well as too much water. All a mulching mower does is keep the cut gr inside the mower for a few more wacks with the cutting bade before it falls out. Thus you end up with very small pieces of cut gr versus long pieces. The short ones can fall down between the gr and become food for the grass. If you wait until the grass is very high then you end up with almost a mulch on top of the grass which isn't good. So cut your grass more often, raise the blade so what's left is 3 inches high.