Trench Composting

A lot of what we do at the Veggie Garden when we start up in spring is weeding. Taking advantage of all this green material, we do trench composting, burying the weeds deep below our veggie beds.

Trench composting is simple: You dig a trench – or any shape hole – 18 to 24 inches deep in an empty space of your garden, add roughly four to six inches of compostable materials, such as kitchen scraps, spent garden plants, small prunings, thinnings, and weeds, and bury them with the soil you dug out of the trench or hole.

The next step is … that’s it! No turning, no watering, no worrying about the ratio between green and brown materials. But you need to wait at least three weeks to use the bed and longer if growing plants with long roots. Most trench composting articles say you can put meat and dairy scraps and even pet waste that you can’t in traditional composting, but some gardeners prefer to avoid them, believing they will attract pests. Flies are not a problem with trench composting because the items are deeply buried, but if you have dogs, raccoons or other digging critters, better skip these ingredients.

Farm animal manures, like those from poultry, rabbits, cows, horses, and sheep, can certainly be trench composted, but be sure to not plant where they are buried for four or more months to avoid any potential pathogen exposure.

So, as we start the Veggie Garden in the middle of March, we sort out the weeds (those that have gone to seed and horsetail are bad – do not bury), let them wilt in pots, then bury them as we turn over the beds.

In the pictures, Veggie Garden volunteers are trenching in the bean bed, which will be used about four weeks later. In this way, less material goes to green waste, and as the weeds decompose, they add humus (a substance that is left over after plants and animals have undergone a long process of decomposition done by earthworms, bacteria, fungi, and other microorganisms) and nutrients to the growing vegetables. Win-win.

– Vanessa Choo, Veggie Garden Coordinator