Can You Leave Pine Needles on the Lawn Over Winter?

A light dusting of pine needles won't harm your grass, but a thick mat will smother it by blocking light and trapping moisture. If you only have a sparse layer, you can leave them be. For heavier accumulations, run a mulching mower over the needles to shred them finely—they'll decompose over winter and actually enrich the soil.

I rely on my mulching mower for this exact reason: it pulverizes leaves and needles so they never form a dense mat. If you don't have a mulching mower, rake up the excess and compost it, or use it as mulch in garden beds where it won't threaten turf.