Trench Composting Your Kitchen Waste

From spring to fall, my veggie garden beds stay so busy growing good things to eat that there is little opportunity to practice the easiest form of composting gloppy kitchen waste, which is to bury it right in the garden. But by the time autumn leaves start fluttering to the ground, I have plenty of vacant space for composting in holes or trenches, which is a good thing! The trimmings from drying and canning apples and pears is more than my enclosed composter can handle, and leaving aromatic fruit in outdoor heaps is asking for trouble from raccoons, deer and other unwanted creatures. So, I bury it.

There is a method to my madness, but it is different from "trench composting", an organised plan in which parallel trenches are filled with organic waste in rotation, so that beds and pathways flip-flop back and forth as each is used as a compost trench. Trench composting would not work in my permanent terraced beds, but what does work is to identify under-achieving beds in the fall, and use them for underground composting during the winter.

Like magic, I have found that fruit and kitchen waste buried about 10 inches (25 cm) deep in October disappears completely by April, when my soil is dry enough to dig. The first year I tried this, I doubted it would work, so I also fermented a big bucket of apple waste, Bokashi style, and did a side-by-side comparison of the rotting progress of fermented vs. raw fruit waste. To my surprise, the raw fruit trimmings decomposed as fast as the fermented stuff, with barely a trace of a core to be found the following spring.

Cathole Composting

When co-author Deb Martin and I were writing The Complete Compost Gardening Guide, we came up with the phrase "cathole composting" for burying and covering over caches of organic waste, just like cats do with theirs. It works amazingly well, and many people use it as a routine composting method. One friend keeps a spade in the bed being composted, and moves it down the row as holes are dug and filled with compostable kitchen waste. Another guy I know covers his holes with a concrete paver, because he uses cathole composting to dispose of fish heads and needs to make sure they are securely buried.

Whenever I am not satisfied with the performance of a bed, I can usually turn things around by peppering it with cathole compost holes filled with autumn food preservation waste, and then covering it with a biodegradable mulch of chopped leaves. I use holes rather than trenches because more soil is exposed to the gazillions of microbes that turn food waste into soil organic matter. When the holes are spaced about 18 inches (45 cm) apart, the columns of soil between them become havens for decomposers from big earthworms to the tiniest bacteria. When the bed is tucked in with a thick blanket of mulch, the stage is set for slow soil-improvement miracles.

More Ways to Compost Underground

Kitchen waste that comes in small pieces, for example coffee grounds or the slurry left behind by your juicer or food mill, disappears so fast when buried that many gardeners dig it into beds that are being actively used to grow plants, including the soil beneath berries and fruit trees. Chunkier materials like broccoli stalks and apple cores take longer to decompose, so it is better to bury them in resting beds, well-covered in deep holes or trenches.

Or, you can make a proper compost pit, as I often do in spring when planting peppers. I dig out a hole and layer in kitchen waste, grass clippings and pulled weeds, then cover it with mulch. I plant three or four capsicum plants around the filled compost pit, which also serves as a moisture reservoir in dry weather. Some gardeners make layered compost pits in fall, and plant tomatoes or pumpkins in the enriched holes in spring.

The most inspirational story on underground compost comes from Bangladesh, where the simple technique of growing edible gourds in holes filled with bags of compost has helped many families survive after floods left their fields buried in sand. I can't help but cheer when something as simple as buried compost saves the day.

By Barbara Pleasant