How long does it take for coffee grounds to decompose?

Coffee grounds should be considered "green material" when added to a compost pile. They are also a good source of nitrogen for the compost. Because of the size and consistency they breakdown fast in the compost pile, faster than other materials so the speed should not be of much concern. Actually, coffee grounds can be spread directly around established plants. Worms seem to love them as food and they quickly incorporate the grounds into the soil so this is a bonus for the plants and soil.