Will leaving fallen leaves on the lawn during winter damage the grass?

Question

I have a lot of leaves on my lawn (in Oklahoma). Will it hurt the grass if I leave the leaves there over the winter?

Answer 1

Yes, if they get matted down - just like covering the grass with anything else would - by reducing sunlight and air circulation.

At least in cooler climates (I'm in New Hampshire), maple and oak leaves will compete with grass for nitrogen - microbes consume it in the leaf decay process. This is why composters like me mix in nitrogen-rich grass clippings - to speed up decomposition. A few trees, like honey locusts, are legumes and are believed to have more nitrogen in their fallen leaves.

Oak leaves are especially acidic, but on the other hand they don't mat as much as e.g. maple leaves because oak leaves curl stiffly and have a more complex shape.

Some folks have good results with shredding leaves and leaving them on. Not me. I suspect this may work well (or at least better) if you fertilize a lot, which I don't.

Grass still grows in the winter, except when it's very cold - just a lot slower.

Answer 2

If you mow over the leaves with a lawn mower and chop them up, they will go between the blades of grass and decompose into the soil. The grass clippings and leaves chopped up make a good carbon/nitrogen ratio for composting. If your leaves are a quickly decomposing type like cherry, a thin layer will not damage the grass during winter, but oak leaves will mat down and deprive the grass of light and oxygen.