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Grass clippings, being mostly water and very rich in nitrogen, are problematic in compost bins because they tend to compact, increasing the chance of becoming soggy and emitting a strong ammonia-like odor. Follow these tips for composting this valuable "green", thereby minimizing odor and matting, and increasing quick decomposition:
Tip #1: Compost in thin layers, intermixed in a 2-to-1 ratio with "brown" materials such as dry leaves or plant debris (saving/bagging Fall's leaves is perfect for Spring/Summer grasscomposting). Always put a thick layer of course brown material at bottom of bin for aeration.
Tip #2: Let grass clippings dry out for a couple of days before composting.
Tip #3: If your bin is stuffed full of grass clippings, turn the pile (use a compost aerator tool) every few days for very fast results. Especially do this to bring air into matted, smelly piles.