Yesterday I redid two of my seven compost piles. The fresh ingredients (shredded leaves, coffee grounds and green veggie wastes)went into the middle. I used a top layer of fairly done material from another pile, one or two inches high. My usual cover is either a piece of used carpeting, or two or three layers of burlap, if available. If the pile is very wet, no cover is used. When rain is expected; the cover is a piece of thick plastic.

The heavy plastic comes from the dumpster at work, the carpeting comes from the neighbors trash pickup, the coffee grounds from Starbucks, the greens from a Chinese grocery store. The burlap has to be purchased, as does the hardware cloth that makes up my bin.

It is normal for a compost pile to have undigested material on the top and sides since those areas are not favored by the bacteria the digest it. The bacteria much prefer the middle of the pile which is why some people turn and mix their compost.