3. Woody ways to build soil

Extracts from Bill Mollison

Hugelkultur
In the carefully tended forests of central Europe, no scrap of wood is ever wasted. Branches and brushy prunings are used in a gardening technique called  hugelkultur, or mound culture. To create a hugelkultur, pile up branches or brush a foot or two deep in a mound 4 to 8 feet long. Stomp on the pile to compact it a bit. Then toss compostable materials—grass clippings, sod, straw into the pile. Sprinkle some compost on the mound, and top with an inch or so of soil. Then plant the hugelkultur with seeds or starts. Potatoes really love hugelkultur. I can start potatoes in these mounds a month earlier than in garden beds. Squashes, melons, and other vines do well here too.

The decomposing organic matter in hugelkultur beds raises the temperature just enough to boost plant growth. Another advantage: As the woody brush rots, it releases nutrients slowly, and also holds quite a bit of water. You don’t need to fertilize or irrigate hugelkultur very often.

The Dead Wood Swale
Perhaps you’ve observed that rotting wood can hold a large amount of moisture. Late in a rainless Northwest summer, I’ve plunged my arm up to the elbow into a rotten log and brought out a fistful of damp pulp. By acting like sponges, downed logs may serve as critical moisture reservoirs for water-dependent species such as fungi and soil animals. Some naturalists theorize that roots and fungal mycelia may translocate water from these woody moisture caches to plants and fungi many feet away.

Rotting wood’s talent for holding water is another of nature’s tricks that can be applied in the garden. We can invert the hugelkultur idea and bury wood beneath our plants. Permaculturist Tom Ward digs trenches about 18 inches deep, tosses in woody trunks or rotten firewood, and then backfills the trenches with soil. On top of this, he plants blueberries. Tom told me, “I’m imitating how, in ponds and bogs, blueberries often root on floating logs. In my garden, all that wood is like a huge sponge sunk into the ground. “The wood soaks up and holds soil moisture, and roots infiltrate this font of wetness and drink from it during drought.

Nearly any plant—not just blueberries will grow well on a buried wood swale. Some people worry that the wood will lock up nitrogen, and thus they toss a nitrogen source into the swale (green compost materials or slow-release fertilizer) but I suspect that the wood decomposes so slowly that very little nitrogen is bound up by the microbes gnawing at the logs.

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