| 23 November 2009 |
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Our Fall Compost Pile Last month our Landscape Maintenance class did some composting. For many it was their very first compost pile, others were veteran composters. Here's what we did, and what we learned along the way: We set up the pile using a very generalized method with a bit of a twist . . . layered brown material (dried leaves, small woody branches, dried grasses, wood chips) and green material (any fresh leaves, stems, roots, vegetables, plant-based kitchen waste) with 2 parts brown to 1 part green. This translates to a C:N ration of around 25:1 (most organic matter in green material is carbon, so 2 parts brown to 1 part green ends up making the pile have 25 times as much carbon as nitrogen). Layers (starting 3' x 3' square) were built from the ground up, in this order.
You can add a composter starter (purchased) but we've found that's not usually necessary. Your plant material and local soil or compost layer have enough microbes to kick-start populations of these critters in your compost pile. Now the twist we used, was done after the pile was built . . . we mixed all layers like tossing a salad. The layers are just a way to keep track of how much brown, green, and soil you put in a pile, to make sure the ratios stay about right. But the layers themselves aren't necessary for actual composting to occur. A fully mixed pile actually will work a bit faster, since the microbes in the soil or compost you added are in closer proximity to organic (green and brown) material to munch on. This 'tosssing' and then turning every other day can actually make finished compost in as little as 2-3 weeks.
What Happened After we finished our compost pile we took its temperature . . . 110 degrees, that was already up 40 degrees from the air temperature which was 70 degrees. Everything looked good, right? Next day we found it was up to 160 degrees and quickly went beyond that to 180 degrees. Ouch! That is way too hot for a compost pile, so hot that all the microbes will get fried and no composting will occur. You want about 130-140 ideally. So what went wrong? It appeared that we added to much green material. Too much nitrogen can overheat a pile quickly. So we added lots more brown material, retossed it, rewetted it and let it be for another day. Two days later, still 160 . . . this was not a compost pile, but a bacteria incinerator! I almost felt guilty. So, we quickly added more brown and kept it wet to bring the temp down. Two days later no change. Finally, I decided to check the accuracy of the thermometer (always good to check your instrumentation that you base decisions upon . . .duh) and found that it had been twisted and stuck with the needle in the max temperature position. I removed the composting thermometer, let it cool, then recalibrated it to the air temperature, then stuck it back in the pile. Aaaahhhhh . . . a nice 140 degrees. The morals of this story are:
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