This hapless fellow is becoming compost the conventional way, in a bin. But his stem will probably still be intact long after he has become humus. For woody materials like stems and branches, mound composting may be a better solution.

Fall is a great time to begin the permaculture practice of hugelkultur, which reminds us that, with gardening anyway, everything worth doing has been done before, even if it’s new to us.

By Sharon Parker
When we moved into a modest bungalow on Fifth Avenue some 20 years ago, we picked what appeared to be the best location for a garden, and were pleased to discover that the spot boasted a rich humus that nurtured a vigorous crop of vegetables, even before we turned our first batch of compost and added it to the beds. Occasionally, to our amusement, we would push a shovel into the ground and turn up a steak bone or other such remnant of somebody’s dinner.

So we weren’t too surprised when one of our old-timer neighborhors told us that Mrs. Nelson, who lived in the house from 1927, when it was built, until about 1980, used to bury her garbage in the backyard. Apart from the occasional beef or pork bone, the only evidence of this long-ago practice was the health of the soil that invigorated our vegetable garden decades later.

I’ve recently gained some new perspective on this practice, called deep composting by some of its advocates today, or mound composting, or, most often, by the German term hugelkultur, which means mound culture. In contrast to regular composting, where we pile our compostable scraps in a heap, to be added to the soil after they’ve broken down, with hugelkultur, the raw material is submerged right where you’re going to plant, with soil mounded on top of it. Notably, this method deals with woody materials that take years to break down, and yields benefits over a longer time span. (But it's probably a bad idea to bury meat and other animal matter, even if it worked for Mrs. Nelson.)

This echoes, in a way, no-till gardening, in which you cover existing sod with multiple layers of newspapers (or leaves), then pile dirt or finished compost on top of that. The smothered sod breaks down under the soil by the time the roots of newly planted vegetables or other annuals reach that far down. To make the whole process a little tidier, frame the bed with boards to make a bottomless “box” about a foot or so deep. Do this in the fall and the soil will be in fine shape by the time you are ready to plant your garden in the spring. Burying the green grass in this way also adds nitrogen to the soil, something fallen leaves alone won’t do, since nitrogen comes from green materials, not brown.

But hugelkultur takes this a step further, using woody plant materials such as branch trimmings from your shrubs and trees, sunflower stalks and squash vines from the garden, or corncobs and broccoli stems from the kitchen (at our house, we call the latter “broccoli bones” and give them to the dog, who happily disposes of them for us). Even heavy logs can be buried, such as the ones at the bottom of the firewood pile that sat too long on the ground and have begun to rot already. Especially those, in fact. But avoid rot-resistant wood like cedar, and allelopathic wood, like black walnut, for reasons that should be obvious, I hope.

Modeled after the natural process of decomposition that takes place in the woods, hugelkultur has caught on with folks in the permaculture movement. Consider how a fallen tree trunk rots, becoming host to lichen, moss, mushrooms and soon more green growing things. Such mini ecosystems last for many years; they foster valuable mycorrhizal relationships between plants, soil and fungi to facilitate the exchange of nutrients, and promote healthy moisture levels.

With mound composting, you bury those tough-to-compost stems, cobs and branches under mounds of softer compostables and soil, either by first digging a trench for the woody stuff or by mounding up raised beds on top of them (or a combination of both, I suppose). The chunkiness of the buried materials also create air pockets, which, as it turns out, are a good thing for roots, according to several hugelkulture advocates.

Woody materials may draw nitrogen from the soil at the beginning of their decomposition process, so you may want to either add some nitrogen fertilizer (organic alfalfa meal would be an excellent choice), or include plenty of green matter such as weeds and grass clippings to get things off to a productive start. Although Toby Hemenway, author of Gaia’s Garden, doesn’t think this is a problem. “I suspect that the wood decomposes so slowly that very little nitrogen is bound up by the microbes gnawing at the logs,” he writes.

It will still take years for the woody stuff to decompose, so you don’t want to do this where you’ll be digging down to plant trees or shrubs next spring; but it apparently makes an excellent bed for potatoes, squash and other vining vegetables. Several sources say berries of various kinds thrive in the mounds, too.

(Potatoes being a root crop, you might wonder about the difficulty of digging into the hugelkultur mound to harvest them -- but the best way to grow potatoes is by laying them on top of the soil and piling compost over them, continuing to mound compost and soil around the stems as they grow, so that the potatoes form along the stems-turned-roots in the compost; which means you’re not going to be digging into the mess of submerged branches at harvest time.)

And hugelkultur practitioners claim that these beds heat up in the spring because of the energy generated by the subterranean decomposition taking place, offering gardeners a head start on the season.

At any rate, I know my husband will be happy if I stop tossing the spirea trimmings and squash vines into the compost -- he complains about them getting entangled in the pitchfork when he turns the pile. I always figure I’m going to sift them out when I want to use the compost, tossing them back in the pile to keep it aerated; and I never bother to turn the pile anyway. But now, instead, I’ll start a hugelkultur mound for those tough-to-compost materials, thus balancing my compulsion to compost (almost) everything and his need for a bit more expediency. Mrs. Nelson would surely approve.

Elements of Gardening is an occasional garden column by Sharon Parker on the Observer Web site.

Further Reading
A good description of hugelkultur, with photographs of a mound being constructed, is offered by a gardening enthusiast who goes by the name Rich Soil.

Gaia’s Garden: A Guide to Home-Scale Permaculture Toby Hemenway (Chelsea Green, 2009)