Agriculture Reference
In-Depth Information
Air
Oxygen is important because we're making aerobic compost. We want to select for aer-
obic microbes because they're the most beneficial. It's not that anaerobic microbes are in-
herently bad, it's just that the way their metabolism works, they often give off gases that
are toxic to plants. So the oxygen content should be at least 5% and preferably above 10%,
although I don't actually keep track of it that scientifically.
Interestingly, the original Indore method perfected by Sir Albert Howard in India in the
beginning of the 20
th
century, the foundation for how we compost today, was largely anaer-
obic because the pile was not turned very often. Most compost piles spend some of their
time anaerobic. In fact, properly made anaerobic compost has some advantages, such as
less nutrient loss, and therefore has some strong proponents. Still, most composters are go-
ing to try to promote aerobic conditions some of the time.
There are two basic methods to ensure there's enough air, and you can use either or both.
The first is to put a layer of brush, branches and sticks on the ground under the pile that is
at least a few inches high. Along with this, if I'm not looking for a finely screened com-
post, I'll include up to 10% twigs in the pile. They won't break down, but they will help
with aeration. Depending on the end use, I may screen those out afterwords, or not.
The second method is to turn the pile over once in a while. You can turn it into a second
bin or bring it out of the bin and back in again. For the fastest decomposition, this is done
whenever the pile starts to cool down from it's hot phase, usually every three to seven days.
Even turning a pile once each season is helpful. In fact, when I'm not in a hurry, this is
what I do because while an unturned or little-turned compost pile takes longer to finish, it
retains more nutrients. If you don't want to go through the trouble of turning the pile, using
a pitchfork or other tool to introduce some air can help.
If you don't want to turn, but need your compost to be done more quickly, you can put
perforated pipe into the pile both horizontally and vertically, or even just put some poles
vertically into the pile that you can pull out after the pile is made. You can use ABS pipe if
you're concerned about toxic PVC. The fastest way to get it done, however, is to turn it
regularly. A “hot” compost pile can be largely done in four weeks. Most weed seeds and
pathogens can be killed in this time. Many nutrients may be lost, but if you have enough
materials, you can make a huge amount of compost in a year using this method. Of course,
it's a lot of work turning the pile and it does contribute many more greenhouse gas emis-
sions.
Some gardeners want fast compost, but don't want to turn the pile often. I don't blame
them. In this case, you can spend more time ensuring aeration right from the beginning, us-
ing the method above and even building the pile one foot off the ground with a sturdy floor
of wood and mesh.
