my theory has always been not to mulch leaves into a newly seeded lawn (grown about 8 weeks before leaves fall and are mulched), because as the leaf mulch decomposes back into soil (compost technically), I'm concerned that the new grass roots and crowns are so small that it might get taken out in the process of the leaves composting back into soil. As many of you know, you can mulch like a 3 foot pile of leaves over a mature established lawn and it won't hurt the lawn, come next spring you'll see none has been killed. Mature grass has a hardier root and crown. But I really do not like removing leaves, so I'm trying to figure out if it's true or not that mulching over a new lawn will kill it. This plot is as best I have for example this year as a newly seeded area even though it was about %65 mature grass seeded a couple years ago, but the other %35 was patches/crabgrass and seeded around Sept 14th this year. All Turf Type Tall Fescue. Then the leaves fell and about 8 weeks later were mulched. I should be able to tell if in Spring I see any patches of no grass even though I don't have a test plot of %100 new grass grown this September. pic of grass blades is how it looks before leaves were dumped on it (it's about %35 new grass). As I mulched the leaves, I blew them closer and closer into a more dense pile. And then there are two pics showing the grass after all leaves were mulched, and 1 pic of a close up of the leaf mulch in the grass blades. Will see what happens in Spring, and I'll give it some spring to bounce back instead of assuming as soon as the weather cracks that there should be grass because the crown may very well still be alive and I will give it a chance to see if it sends new blades up.