engines of production." Anyone who has not read his visionary book,
_Tree Crops, _should. Though written in 1929, this classic book is
currently in print.

Once each year, leaves are available in large quantity, but aren't
the easiest material to compost. Rich in minerals but low in
nitrogen, they are generally slow to decompose and tend to pack into
an airless mass. However, if mixed with manure or other
high-nitrogen amendment and enough firm material to prevent
compaction, leaves rot as well as any other substance. Running dry
leaves through a shredder or grinding them with a lawnmower greatly
accelerates their decomposition. Of all the materials I've ever put
through a garden grinder, dry leaves are the easiest and run the
fastest.

Once chopped, leaves occupy much less volume. My neighbor, John, a
very serious gardener like me, keeps several large garbage cans
filled with pulverized dry leaves for use as mulch when needed. Were
I a northern gardener I'd store shredded dry leaves in plastic bags
over the winter to mix into compost piles when spring grass
clippings and other more potent materials were available. Some
people fear using urban leaves because they may contain automotive
pollutants such as oil and rubber components. Such worries are
probably groundless. Dave Campbell who ran the City of Portland
(Oregon) Bureau of Maintenance leaf composting program said he has
run tests for heavy metals and pesticide residues on every windrow
of compost he has made.

"Almost all our tests so far have shown less than the background
level for heavy metals, and no traces of pesticides [including]