Laurel Valley Soils are the king of compost. Located in the capital of mushroom growing country in southeast Pennsylvania . They collect spent mushroom soil from mushroom growers and work and put it through a really effective composting process. The result is a nice screened compost that is still loaded with nutrients (the mushroom growers get rid of it befor it is totally spent). They have a greens grade that can easily be spread with topdressing machinery.