simultaneously turns and sprays water, mechanically oxygenating and
remoistening a massive windrow every few days. Even poorly-financed
municipal composting systems have tractors with scoop loaders to
turn their piles frequently. At home the practical limit is probably
a heap six or seven feet wide at the base, initially about five feet
high (it will rapidly slump a foot or so once heating begins), and
as long as one has material for.

Though we might like to make our compost piles so large that
maintaining sufficient airflow becomes the major problem we face,
the home composter rarely has enough materials on hand to build a
huge heap all at once. A single lawn mowing doesn't supply that many
clippings; my own kitchen compost bucket is larger and fills faster
than anyone else's I know of but still only amounts to a few gallons
a week except during August when we're making jam, canning
vegetables, and juicing. Garden weeds are collected a wheelbarrow at
a time. Leaves are seasonal. In the East the annual vegetable garden
clean-up happens after the fall frost. So almost inevitably, you
will be building a heap gradually.

That's probably why most garden books illustrate compost heaps as
though they were layer cakes: a base layer of brush, twigs, and
coarse stuff to allow air to enter, then alternating thin layers of
grass clippings, leaves, weeds, garbage, grass, weeds, garbage, and
a sprinkling of soil, repeated until the heap is five feet tall. It
can take months to build a compost pile this way because heating and
decomposition begin before the pile is finished and it sags as it is
built. I recommend several practices when gradually forming a heap.

Keep a large stack of dry, coarse vegetation next to a building