Cohousing-L Mailing List: Re: Compost

[Douglas G. Larson (ddhle]

I would be happy to share experiences and photos. I was certified as a Soil
Foodweb advisor in 2006 and we have been actively doing hot composting here
at Songaia Cohousing for 4 years. 


Our hot composting site is a 5-bin system that one of our residents designed
and built 4 years ago. 

The first bin is simply a collection bin for garden waste. It has wire fence
sides to contain it and is open in the front. 

The 2nd bin is wood on 3 sides and open in the front. We use this as a prep
bin, i.e. we use a power chipper to chip everything from the collection bin
into this.

Then we have 3 processing bins, each about 1.5 cubic yards. They are wooden
sides each with a lid. The front of each are 2x4's stacked in a slotted
grove so removal of the front is easy. The 2x4 fronts as well as the other 3
sides have spacers so air can get into the bin. 

If you read books on composting you will find that all of them state that
the bin should be a minimum of 1 cubic yard, i.e. 3-ft x 3-ft x 3-ft. But
when we built our bins I asked that they be 1.5 cubic yards. The larger
volume makes it slightly easier to build heat but not so big that labor
becomes unmanageable. So our bins are about 4-ft x 4-ft x 4-ft. 


As you are probably aware, there are 3 composting methods - 

Hot composting - also known as thermophilic composting where a pile is built
and quickly comes to a high heat (around 120 to 150 degrees F). This
requires frequent monitoring and turning. It is the most labor intensive of
the three methods but can produce finished compost in about 2 months. 

Static composting - This is where you build a big pile and don't do much to
it. You might turn it once or twice during its process but otherwise it
requires little work. This method takes from 8 months to a year to produce
finished compost. 

Worm composting - also known as vermicomposting. This is where worms do most
of the work. This method works best on food waste and requires special worms
and special bins designed for this purpose. If left unattended or filled
incorrectly the whole batch of worms can die, leaving you with a mess to
clean up. But if done correctly it will produce finished worm compost
continuously. You simply remove the finished compost from the bottom and
keep adding food waste and shredded paper to the top. 



Our hot compost bins are set in concrete footings that hold the wood frame
but the bottom of each bin is simply open to the earth. While our bins do
have lids, designed to prevent rats from entering we do have rats that dig
under ground into the bins. The rats are a bit annoying but otherwise
haven't been a huge problem. 

I have some comments on your requirements for your new bins - 

Rat proof -  this will be a bit difficult to achieve but probably doable if
you have concrete floors and bins designed to allow air in but not small
animals. 

Odor free - The presence or absence of odor is due mostly to how you build
and maintain your piles. Compost, even during the processing stages, while
not odorless, doesn't stink. The stink is due to the pile becoming
anaerobic, i.e. not enough oxygen in the pile. Under these conditions
anaerobic bacteria and fungi are taking over and they produce exudates that
produces the stink (e.g. alcohols and other nasty smelling substances). The
substances that produce the stink are not only unpleasant but they are not
good for your plants if the material is spread on the garden. 

Three things will promote anaerobic conditions 
  1)  Too much high nitrogen content. All food waste and scraps are high
nitrogen. 
       Grass is another example of high nitrogen item. When your C-N ratio
tips too far 
       to the nitrogen side, this promotes anaerobic conditions. 

  2)  Not enough air in the pile. This happens when the material is too
finely chopped 
       and so fits together very tightly leaving less room for air to enter.
You do want to 
       chip the yard waste and some of the food waste because it will break
down 
       faster. Five percent, by volume, of a newly built pile should contain
sticks and 
       twigs about the diameter of a pencil. This helps create air pockets
in the pile. You 
       can also insert 1 or more air pipes as you build the pile. 

  3)  There is too much water in the pile which tends to prevent air from
entering. All 
       piles do require the presence of water but too much water isn't a
good thing and 
       promotes anaerobic conditions.  

In our piles we use a 4-inch diameter perforated plastic drain pipe that we
insert in the middle of each new pile. The pile sticks up above the top of
the pile and facilitates air circulation. It works quire well for us. In
addition the walls of our bins have openings that allow air to enter. 
Our piles do sometimes become anaerobic and stinky when we have put in too
much green material but we then turn more often which brings in more oxygen
and reduces or eliminates the stink. 

Aesthetic -  This is largely a personal preference but well built bins can
be attractive. 


Efficient and effective for residents - This is a somewhat complex mix of
bin design and maintenance practices. The larger your bins are the more
labor will be required to turn and maintain them. The bins need to be
situated with plenty of space to walk around and work when building the
piles and when turning them. 


Here at Songaia we compost our kitchen scraps as well as our yard waste.
Both are in abundance. For the food scraps we keep 4 plastic waste cans (33
gallon size) with lids outside of our dining room. We don't allow meat or
dairy in our food waste but otherwise everything goes into these waste cans.
The composters take these waste cans and cart them down to the compost bins
when its time to compost. The yard waste is already there in our collection
bins. We have a water faucet next to our compost bins for easy access to
water. 

We have 3 compost thermometers that we insert into each bin. Its an easy way
to monitor the temperature. These are available online at several places.
But some of them are not very good thermometers. I have found that the
Tel-Tru brand compost thermometer is excellent. The price depends on how
long of a stem you get. We use 18-inch stems and Tel-Tru sells these for
about $40. They have a longer stems as well as larger dials that sell for
more.   http://www.teltru.com 


The temperature in a hot compost pile should reach 120 to 150 degrees F and
stay there for at least 5 consecutive days. A pile hotter than 155 should be
turned immediately so a thermometer helps with that decision. 

We have a chipper we use to chip everything, yard waste and food waste
alike. It makes building the piles easier and more manageable. These
machines are expensive (starting around $400 and going up to over $1200) but
they are indispensible if you are composting a moderate to high volume of
material. They are also very noisy. We wear hearing protection every time we
use them. The Elvex company sells very good ear protection at very good
prices. http://www.elvex.com/ 


I will take some photos and send them to you later. 



Douglas Larson,
Songaia Cohousing - Bothell, Washington