By Diane Kennedy.
Hügelkultur (hoo-gull culture) has ancient origins in the mountains of Germany, where warmth is treasured and rain is frequent. There they stack logs and branches into a mound, pack dirt around each piece of wood, cover it with straw and then plant on it. Planting season comes weeks earlier on the warm, frost-free mound. The old wood acts like a sponge absorbing rainwater and slowly releasing it into the surrounding drying dirt. As the wood decays it feeds microbial communities in the soil.
In Southern California we have the exact opposite climate issues, low rainfall and lots of heat. Here we practice hügelkultur in reverse: we bury the wood in the ground.
Old logs are the best materials for hügelkultur; that stack of logs which is now an excellent squirrel and Black Widow home has true value in the soil. If you have existing plants and trees, bury old wood outside of their driplines. If you are planting, break up sticks and scatter them around the bottom of the planting hole. If the wood is sourced from your own property you will also be ‘planting’ site-specific beneficial microbes. Wood left above ground releases carbon into the atmosphere, but once buried the carbon is made available to plants. It is important to cover each piece of organic material with dirt: don’t just cover a mound of sticks with dirt. You only need an inch or so of dirt on top.
Not all of us are blessed with large dead tree stumps. You can bury anything that will decompose and it will eventually rot and help fertilize the ground. Old lumber, if it isn’t pressure-treated or painted with oil paint, is great to bury. Palm fronds and trunks are excellent. Green softwood cuttings will cause a slight nitrogen burn until they ‘die’ so bury them where you won’t plant for a season. The same for eucalyptus peppertrees (Schinus), walnut, and others that produce a compound (allelopathy) that retards the growth of many plant species in their vicinity. Mostly the retardant is in the form of volatile organic compounds and will dissipate over time. Diseased and infested wood should be avoided.
Use hügelkultur in conjunction with earthworks to hold water in the soil. Swales are level-bottomed ditches that run perpendicular to the water flow. They run the same as topographical lines, so that they capture water. You can dig a swale on a small scale with a shovel above your trees, and place wood so that it is buried on the downward side of the swale. Plant just below that. Water will run into the swale and sink into the soil, be absorbed by the aging wood, and then will be available for the roots of the plant over time, along with nutrients from the wood.
Hügelkultur your pots. Line the inside with cardboard to insulate the roots from heat, break up some brown sticks and throw them in with the potting mix. The sticks help water and fertilize your plant.
Hügelkultur is a great way to sequester carbon, improve sandy or clay soil, keep wood out of the landfill, repurpose cut trees and shrubs, add long-term natural fertilizer to the soil, feed your microbes, hold water in the soil, and make squirrels frustrated. When you cut a tree or shrub, you will be harvesting branches and leaves for the health of your garden rather than sending the best fertilizer you’ll ever need to the dump. See what wood is laying around your yard, and bury it.