Last update: January 27, 2017
Hot composting is far more common than cold composting. While hot composting is a fine place to start as a beginning composter, it is important to remember that it is—on a global scale—less sustainable.
The question still remains: Why cold compost?
More compost out for the materials you put in.
Hot composting usually only yields about 25% to 33% cured compost per unit of built material volume. In contrast, Ecology Action (EA) has found that cold compost can yield about 35% cured compost per unit of built material.
To make that more concrete, let’s say that you grew a beautiful patch of sunflowers this year, and you save your garden waste and kitchen scraps to combine with this to make compost. You can’t decide whether to use a cold composting or hot composting method, so you decide to give both a try. The recipe for the hot pile is in our first compost blog, ‘Composting: The Easy Way to Healthy Veggies’. The recipe for the cold pile is at the end of this article. You split your harvested sunflower stalks between the two piles (built, of course, the same 3′ x 3′ x 3′ size) and you add in the appropriate amounts of immature material (including any kitchen scraps) and soil to each pile. Then you wait and watch. You’d notice that the hot pile’s temperature is at its peak for about three weeks and then drops, and the cold pile is hot at a similar peak for only about one week and then drops. But that’s not all you’d see.
In EA’s research (three trials during the main growing season), it was found that after about three to four months, the hot compost piles were ready for use. (The pile was unturned during the three months.) The cold piles took a bit longer, averaging a curing time of about three months and two or more weeks.
But, at the end of about three to four months, you’d also notice that your hot compost pile produced less cured compost than your cold compost pile. Your hot pile, for the amount of materials you put into the pile, would only give you 25% (or possibly up to 33%) the amount of cured compost by volume. But your cold compost pile could return about 35% of what you put in. All in all, this means more cured organic matter for growing a living soil.
Many people ask why this should matter. If we are looking at large-scale sustainability, it is important to look at utility and usability. That means, as much as possible, making sure that the soil is healthiest by using our garden waste most effectively. Rather than buying compost that takes from other people’s resources, using our own compostables to their utmost.
Now to clarify some aspects of hot composting and cold composting:
Hot composting kills all the bad guys?
False. Hot composting only kills 25% of insect larvae, weed seeds, pathogens. To kill all of these, the compost would need to get to 178°F., instead of averaging a much lower temperature. To do this would burn up a lot more carbon and result in less cured organic matter.
Cold composting takes a lot longer?
False. As mentioned before, depending on the climate, cold composting doesn’t take much longer than hot composting.
Cold composting requires more work?
It requires less work.
Hot composting, as normally practiced, may take some extra work if the pile is turned. All compost piles require separating out the less-decomposed material at the end. The cold pile is left alone for a few months, and watered to continue its moldering process; it has some more undecomposed material.
One method creates more humus in the compost?
Humus is a complex topic (that we will explore in later blog posts), but the basic knowledge each gardener should know is this: Humus is both living and dead microbial life, and is a stable type of carbon in the soil. It is important to retain water in soil, and it provides structure in soil, allowing the soil to hold air.
In a sense, humus is key to the life in our soils. Thus, one of the great aims of GROW BIOINTENSIVE gardening is to maximize the health in our soil, which means a compost pile producing the most humus possible.
Basically, depending on how carefully you build and monitor your compost piles, you can maximize your humus in your piles. (Stay tuned for our later post on this technique.) So both hot and cold composting can create humus but cold composting can produce more per unit of built material.
So here’s the takeaway: Cold composting allows you to reap more cured compost, and you also get more humus.
This diagram shows the structure of each layer of a GB Cold compost pile, C/N 60/1 ratio, as it is built up from the ground:
|TOP (more layers are built on top as needed, and a full 5-Gal. bucket of soil is used to “cap” the top of the pile.)
|,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,||Thin layer of Soil — one quarter of a 5-Gal. bucket|
||||||||||||||||||||||||||||||||||||||||||Immature material: spread evenly over the layer — 0.5, 5-Gal. bucket|
|==================||Mature material: spread evenly over the layer — 2.5, 5-Gal. buckets|
|%%%%%%%%%%%%||A 4” thick layer of mature woody material as the base|
|BOTTOM (ground level)||Loosen soil about 12″ deep.|
For more details, see Compost Sections in:
The Farmer’s Mini-Handbook, Margo Royer-Miller, Ecology Action, 2010. Free, downloadable at: http://www.growbiointensive.org/Self_Teaching.html
(A good hot composting resource.)
The Sustainable Vegetable Garden, John Jeavons and Carol Cox, Ten Speed Press, 1999. Available from Ecology Action’s non-profit Mail Order Service, www.bountifulgardens.org
(A good hot composting resource.)
How to Grow More Vegetables—and Fruits, Nuts, Berries, Grains and Other Crops Than You Ever Thought Possible On Less Land Than You Can Imagine, John Jeavons, Ten Speed Press, 2012. Available from Ecology Action’s non-profit Mail Order Service, www.bountifulgardens.org.
(A good hot and cold composting resource.)
To learn more about Ecology Action’s research on compost, see:
“GROW BIOINTENSIVE Composting and Growing Compost Materials”, Ecology Action Staff, Ecology Action, 2004. Available from Ecology Action’s non-profit Mail Order Service, www.bountifulgardens.org
If you found this information helpful, consider supporting our education programs in local schools by making a contribution:
By sending a check made out to Ecology Action, to Ecology Action, 5798 Ridgewood Rd., Willits, CA 95490. Note on the check that it is for: Common Ground Garden Local School Education.