Bastard Trenching

Bastard trenching is actually an alteration of trenching that is practiced during the first few years of digging a new area as a method to keep from mixing the layers of soil before each is evenly improved by deep loosening and the addition of large amounts of organic matter. Gardeners who mean to trench their garden take care not to mix their layers of soil for two reasons:

First, until the soil has been thoroughly loosened to provide sufficient pore space for air transfer deep in the soil, the soil below a foot deep contains anaerobic microbes instead of the aerobic microbes present in the upper foot. The thought is that inverting these layers puts aerobic microbes where they no longer have the air they need and anaerobic microbes where they’re exposed to air, killing large numbers of both. In truth, it won’t kill all of either, but it may take longer for the aerobic microbes to repopulate the upper areas. And these gardeners want to do everything possible to encourage, not impede, their soil microbes.

Second, until the soil has been improved with sufficient added organic matter, sending the topsoil, rich in organic matter, to the depths and replacing it with unimproved subsoil does little to help plants. If they grow big enough, they’ll reach the now-deeper topsoil, but they’ll struggle starting out in the unimproved subsoil, while the rich topsoil is out of reach of young plants when they desperately need it.

Thus, gardeners who will eventually trench their gardens use bastard trenching to avoid mixing their layers of soil for the first several years until all of the soil in the top two feet is evenly aerated and enriched with organic matter.

Bastard trenching accomplishes keeping the layers separate with two slight but ingenious changes: First, the soil that is dug from the one-to-two-foot-deep layer in the initial trench is set aside separately from the soil from the top foot, and each pile of soil is added back on the far side of the bed at its original depth. Second, an additional one-foot-deep trench is dug adjacent to the first, creating a shelf-like configuration that allows the layers to be moved over separately as soil and trenches are leapfrogged down the garden.

After several years of bastard trenching, gardeners can trench without worrying about mixing the top two feet of soil since their soil is essential uniform at all depths. It’s a great method and a simple alteration to avoid mixing layers before all of the soil is significantly improved. It was only called bastard trenching because it wasn’t the “true” trenching that could be done once the soil was evenly and thoroughly improved through loosening and adding organic matter to three feet deep.

Over time, it seems the “bastard” part of this became misunderstood and applied by some to those gardeners who only trenched two feet deep, as some today call double digging “bastard trenching.” Double digging, however, is actually just a more recent, if a foot shallower, version of trenching.