Monday, August 2, 2010

A Little Compost Math

I have been noticing lately that my homemade tumble composter has been getting harder and harder to turn, even though it has remained about the same level of full since I made it. One of the constants of compost is reduction. Assuming you do it right, it will continue to shrink in volume. Part of this is because the raw materials have so much space in them and they pack down as they decompose. However, a bigger part is that a very large amount of the mass, around 50% is converted to carbon dioxide or other gasses as a part of the decomposition process. As the carbon is lost, the minerals and nutrients get distilled down to a concentrated, nutritious form.

It occurred to me that I have been constantly filling this single 55 gallon drum since January. I started it with enough dry leaves to fill it one and a half times. I actually had to fill it and then wait to cram the rest in. I have added at least three baskets full of weeds, each a third to a half the volume of the compost bin. I added the remains of a previous compost pile that weren’t quite done cooking. Then there is the constant supply of kitchen waste. So I decided to do a little math to see just how much kitchen waste I have generated.

First of all, there is my kitchen compost bin. It is 11”x6.5”x10”, which gives me a total volume of about 0.41 cubic feet. I assume it was an average of about ¾ full when I took it out, so three trips would be a cubic foot. I figure I took it out about three times a week on average, so I generated about one cubic foot of compost a week. My compost bin is 55 gallons, which converts to about 7.5 cubic feet. That means I generated enough kitchen waste to fill it completely every 2 months or so, and have done so since January, so the kitchen waste alone has been enough to fill it about 3.5 times. Add to that the one and a half full worth of dry leaves and another filling or so for weeds and other materials, and I have filled it with enough material to fill it completely about 6 times. Yet it remains only about three quarters full, just as it has almost constantly since I put the first load of leaves in and wetted them down.

My compost is now getting heavy, which means it is getting dense. Perhaps it is time to stop filling it and let it finish cooking so my garden can have an infusion of nutrients and biological activity. I know I am itching to make some compost tea for sure.

And yes, I do this for fun. Did I mention I am a garden geek?


  1. Thats why I have two.
    Also, if you have potatoes, they can handle really rough compost, just mentioning that as sometimes I take my scraps right to the potato bins.
    One confession: I am not always very upset when some produce goes bad in the fridge -unless I grew it.
    I see it as potential.

  2. This is my first time i visit here. I found so many entertaining stuff in your blog, especially its discussion. From the tons of comments on your articles, I guess I am not the only one having all the enjoyment here! Keep up the good work.