The Manic Gardener - An Organic Gardening Blog: Hot compost, anyone?

October 26, 2009

Hot compost, anyone?

Should you drop by to visit, some bitterly cold night, and find my house locked, and should you be so lacking in good sense or hard cash that you don’t just head for a hotel on Main Street a mile away, I invite you to climb into my latest compost pile. Granted, it’s both damp and dirty, but it’s several cuts above Luke Skywalker’s accommodations, the night he spent in the belly of the beast. And it’s guaranteed to keep you warm. In fact, you might get burnt: the temperature is over 140°F.

This, my latest and greatest pile, consists almost exclusively of pine duff, leaves, and apples--along with a generous supply of corn gluten meal for nitrogen. By “greatest” here I refer not merely to its physical dimensions, though those are not insignificant--the fork on the right gives some idea of its size--but to its unlikely and resounding success, given that it was built in cool weather of material generally not considered compost-friendly.

What you see above is actually the second incarnation. The first went up two weekends ago--on Sunday, October 18th, to be precise--as an experiment. The pile hit the “hot” zone (over a hundred and thirty) within days, and cooked along at 155° for the rest of the week. (I kept a pretty close eye on it to be sure it didn’t go above 160°F (71°C), at which point even beneficial organisms begin to die off.)

When the temperature dropped all the way down to 145°, I decided it was time to move on to stage two. One’s usually advised not to turn a hot pile until it drops below 100°, but cool weather was on the way, and as I wanted to incorporate a lot of new material (another no-no), I thought I’d best take advantage of the heat already in the pile.

So yesterday I filed my wheelbarrow with brown apples in one neighbor’s yard, overfilled it with sodden leaves from the street, and mixed these ingredients into the pile as I forked it over. (That makes the task sound deceptively easy, which isn't how it felt.) By the time I finished, the air temp was about 34°--and just above freezing is not prime composting weather--but the thermometer in the pile read almost 70°.

Since I added no more corn gluten meal, I thought the carbon content might overwhelm the available nitrogen--but somehow suspected otherwise. Also, though I’ve not been able to track down a nitrogen content for apples themselves, table scraps in general have about 10-15% nitrogen. I also added no more water, but some of the leaves were wet, and the apples, of course, contain a lot of water, which I assumed (gulp) would become gradually available.

What with all the risks I’d taken--cool weather, no more nitrogen or liquid--it seemed possible that I’d just killed off a great pile, so I approached it this morning in some trepidation. Here’s what I found:

145 degrees