University of Vermont Extension
Department of Plant and Soil Science
COMPOST HAPPENS, OR DOES IT?
Dr. Leonard Perry, Extension
University of Vermont
A compost pile only makes desirable
compost for the garden if conditions are proper. There are certain signs to watch for that
your compost bin may need some help.
If your compost has a rotten smell,
this may mean your compost is too wet or too compacted. In either case, sufficient air isn’t getting
to the microorganisms that are what make materials decompose into the final
compost. To add more air, turn the pile
with a garden fork or similar tool. You
can add a dry, porous material such as sawdust or straw if the pile seems too
wet. Another option is to break a larger pile into smaller ones.
On the other hand, if you smell
ammonia, this indicates there is too much nitrogen and not enough carbon. These same microorganisms use carbon for
food, and nitrogen to make proteins.
Without these, or with the improper balance, the microorganisms wont do
their job effectively. So if you smell
ammonia, add more high carbon material such as straw and less high nitrogen
materials such as grass clippings and vegetable scraps.
You should aim for about 30 parts carbon
to one part nitrogen, by weight, although this doesn’t have to be
exact. Coarse, woody material such as twigs, leaves
and paper are usually high in carbon.
Moist, dense material such as manures are high in nitrogen. A
rule of thumb some use is that brown
indicates carbon, and green indicates nitrogen.
Lush, green grass clippings are a great source of nitrogen, even
if you fertilize your lawn. However, in general,
it is best to mow regularly leaving clippings on the lawn.
A problem I have in our colder northern
climate is the compost pile not heating up properly. Composting microorganisms do their job in the
range of 95 to 160 degrees F. Too low and
they work slowly if at all. Ideal in the
interior of compost piles is about 120 to 130 degrees F. Temperatures can be measured with compost
thermometers—basically a dial on a long rod—obtained at complete garden supply
stores or online.
If over weeks or months your compost just
isn’t progressing, or the season is cool, consider if your pile is too
small. Large piles hold heat in the
interior better. Not enough moisture, poor
air circulation, and lack of nitrogen also are reasons the compost pile might
not be heating up properly. In addition
to tips already mentioned, try insulating the pile with straw to hold in heat
Another reason compost might be
progressing slowly, if at all, is that the acidity is too acid or
alkaline. These same microorganisms
prefer a neutral to slightly acid environment.
Many materials you add to compost are acidic, hence the reason a
sprinkling of lime often is recommended.
Too much lime, or too many wood ashes which serve the same purpose, and
the pile will be too alkaline (high pH).
You can check this with inexpensive soil test kits from garden
stores. Add more materials if the pH is
Got pests? Raccoons, chipmunks, and even rats are
attracted to meat scraps or fatty good wastes in the pile. Don’t add
these types of waste. Also, don’t add weeds from your garden, if
they have gone to seed, nor diseased plant parts. These will cause
future garden problems.
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