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Compost Guide - Composting Fundamentals
What NOT to Compost
Whether because of toxins, plant or human diseases, or weed troubles,
there are some things that shouldn't be put into compost piles. Avoid
composting the following materials:
CHEMICALLY-TREATED WOOD PRODUCTSSawdust is often
available from constructions sites, friends, or your own building
projects. If you are considering composting sawdust, be sure of the
origin of the sawdust. Sawdust from chemically-treated wood products
can be bad stuff to compost. For example, take
pressure-treated wood (sometimes called CCA), which usually has a
greenish tint to it (I have also seen it in other colors). It
contains arsenic, a highly toxic element, as well as chromium and
copper. There is evidence to suggest that arsenic is leached into the
soil from these products when they are used to make compost bins or
raised beds, so composting the sawdust would certainly be a mistake.
You may wish to read the 'Letters' section of Organic Gardening, April
1994 and July/August 1992, for more information. Avoid other
chemically-treated wood products and sawdust as well, such as wood
treated with creosote or 'penta' preservative.
DISEASED PLANTSMany plant disease organisms are killed by
consistent hot composting, but it's difficult to make sure that every
speck of the diseased material gets fully composted. It's best not to
compost diseased plant material at all, to avoid reinfecting next
year's garden.
HUMAN WASTESHuman feces can contain disease organisms that
will make people very sick. Composting human feces safely requires
that the compost pile reach high (thermophilic) temperatures over a
period of time. It isn't necessarily that difficult to reach these
temperatures in a home compost pile, but the potential health costs of
improper composting are high. Composting of human feces should not be
attempted, except by experienced 'hot pile' composters who are well
informed of the temperatures and times required to kill pathogens, and
who are willing to take 100% responsibility for the process and
product. If you would like to learn more about composting humanure, I
recommend The Humanure Handbook, listed in the resources
section of the Rot Web.
MEAT, BONES, AND FATTY FOOD WASTESThese materials are very
attractive to pests (in an urban setting, this could mean rats...).
In addition, fatty food wastes can be very slow to break down, because
the fat can exclude the air that composting microbes need to do their
work.
PERNICIOUS WEEDSMorning glory/bindweed, sheep sorrel, ivy,
several kinds of grasses, and some other plants can resprout from
their roots and/or stems in the compost pile. Just when you thought
you had them all chopped up, you'd actually helped them to multiply!
Don't compost these weeds unless they are completely dead and dry (you
may want to leave them in a sunny place for a couple of weeks before
composting). Remember also that composting weeds that have gone to
seed will create weeds in next year's garden, unless a very hot pile
temperature can be maintained to kill the seeds.
PET WASTESDog and cat feces may carry diseases that can
infect humans. It is best NEVER to use them in compost piles. Some
people do bury them 8" deep in the soil, but ONLY in areas where food
crops are never grown.
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