GRASS/LAWN CLIPPINGS

Actually, it's usually easier to leave grass clippings in the lawn,
where they will decompose and benefit the soil directly. However,
they can be composted, too. Be cautious to add grass clippings in
very thin layers, or thoroughly mix them in with other compost
ingredients, as they otherwise tend to become slimy and matted
down, excluding air from the pile. Fresh grass clippings are high in
nitrogen, making them a 'green' compost ingredient.
 

HAY

Farmers are often very happy to get rid of spoiled hay bales that
have been out in the rain, and will give them away or sell them at a
low price. Grass hay will probably contain a lot of seed, which can
resprout in your garden. Alfalfa hay will compost very readily. The
greener the hay, the more nitrogen it contains. Be sure that any hay
you plan to compost is well-moistened prior to addition to the pile.
 

KITCHEN WASTES

Fruit and vegetable peels/rinds, tea bags, coffee grounds,
eggshells, and similar materials are great stuff to compost. They
tend to be high in nitrogen (this puts them in the 'greens' category),
and are usually quite soft and moist. As such, kitchen wastes need
to be mixed in with drier/bulkier materials to allow complete air
penetration. Many people compost their kitchen wastes in
enclosed worm bins or bury them 8" deep in the soil, to keep from
attracting pests to an outdoor compost pile (check with your local
government to see if it has regulations about this -- some forbid
open piles containing food wastes because of the pest issue).
Avoid composting meat scraps, fatty food wastes, milk products,
and bones -- these materials are very attractive to pests.
 

LEAVES

If you live in an area where autumn leaves are still thrown away as
garbage, cash in on the bounty each year by acquiring your
neighbors' leaves! Generally, leaves are an excellent compost
ingredient. They can mat down and exclude air, though, so be sure
that any clumps are thoroughly broken up, or that the leaves are
only used in very thin layers. Ash and poplar/cottonwood leaves
can raise soil pH if used in compost -- this may not be beneficial if
your soil is already alkaline, as many soils are in the West
(especially in semiarid and arid climates). Dead, dry leaves are in
the 'browns' category, while living green leaves contain abundant
nitrogen and are considered 'greens'.
 

MANURE

Horse, cow, sheep, and poultry manures are often available for
free from local ranches, farms, and stables. They can burn plants if
applied when fresh, so be sure they get well composted. Manures
typically contain quite a bit of nitrogen (the fresher the manure, the
more nitrogen it contains) and are considered a 'green' ingredient.
Some manures may contain weed seeds. Fresh manures can get a
compost pile to heat up quickly, and will accelerate the
decomposition of woody materials, autumn leaves, and other
'browns'.
 

STRAW

Dry straw is a good material for helping to keep a compost pile
aerated, because it tends to create lots of passageways for air to
get into the pile. Be sure to wet the straw, as it is very slow to
decompose otherwise. Straw is definitely a 'brown' and also
requires mixture with 'greens' to break down quickly. Many
stables use straw as a bedding material for horses -- straw that has
undergone this treatment is mixed in with horse manure and breaks
down more quickly.
 

WEEDS AND OTHER GARDEN WASTES

Many types of weeds and old garden plants can be composted.
Avoid weeds that have begun to go to seed, as seeds may survive
all but the hottest compost piles. Some types of weeds are
'pernicious weeds' and will resprout in the compost pile -- avoid
using these unless they are thoroughly dead. Green weeds are (you
guessed it) a 'green', while dead brown weeds are a 'brown'.
 

WOOD CHIPS AND SAWDUST

Wood products belong in the 'browns' category, because they are
fairly low in nitrogen. Some sawdusts, especially from
broadleaved/deciduous tress, will break down quickly in an active
compost pile. Others, especially from coniferous trees, will take
longer to decay. Stir sawdust thoroughly into the pile or use very
thin layers. Coarse wood chips will very slowly decay, and are
probably better used as mulch unless you have lots of time to wait.
Be sure not to compost chips or sawdust from any sort of
chemically-treated wood -- you could be adding toxics like
arsenic to your pile if you do.

What NOT to Compost
Do not add the following items:

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 PRODUCTS

Sawdust 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 PLANTS

Many 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 WASTES

Human 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 WASTES

These 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 WEEDS

Morning 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 WASTES

Dog 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.