Wednesday, February 8, 2012

Hillside Hugelkultur and Swaling, pt 1 : Concepts and planning

"Are you looking for firewood? Y'know that stuff won't burn right, it's all soggy and rotted!"
"That's okay, I'm deliberately collecting rotten stuff."

- The generalized form of a conversation I hold every time folks find me loading their waterlogged curbside junkwood, sacks of yard waste, and so forth into my vehicle.

     As a result of permaculture training this past summer, the concept of hugelkultur firmly lodged itself in my gardening outlook as a beautiful blend of most everything I like in terraforming - low impact, high yield, zero cost, immediately practical, and conducive to long-term positive change. Although the link I embedded gives a long and excellent overview of the topic, the shorter version is this: lay down a bunch of rotting wood, dump soil on top, plant things. The rotting wood, once "charged" with water, provides a slow and constant source of water, minerals, fungi, bacteria, microorganisms, soil insects, and so forth to the soil and roots around it, acting as a giant goody-sink that plants can draw on for years as it slowly decays. It also helps to effectively sequester the carbon bound up in the wood, as much of it gets turned into soilborne organisms and soil, rather than reverting to atmospheric carbon dioxide, its much quicker fate if it just breaks down on the surface, or gets burned.
     By some calculations, the amount of carbon sequestered in soils worldwide, as abiotic carbon, soil organisms, slow-rotting material, etc - weighs in at 2.7 trillion tons, whereas all of the living matter on Earth makes up only 575 billion tons, most of it locked up in trees. As it turns out, deforestation ends up being a greater problem due to soil erosion, and its consequential loss of soil-bound carbon, than due to direct loss of the trees. This makes hugelkultur completely awesome both to jumpstart rapid nutrient-fortifying, carbon-banking, sassypants-delicious soil farming, and also because the mounding system hugelkultur lends itself to allows for easy earthworks, as you can lay the mounds down in lines to divert, capture, and better utilize water flow in an area. This ties back into the manifold benefits of large-scale carbon banking in the soil, a major one of which is increased soil capacity for water storage (just think of how moist, alive with life, and earth-smelling a handful of rich black loam is when you scoop it off the floor of an old forest, and compare that picture with a handful of beach sand - the major difference comes down to total carbon present.)
     However, talk is cheap. So on to implementation!

Genesis point
This shows my starting point. This small hillside in the front yard faces northeast. It's growing nothing, as you see, but patchy grass; the soil has no depth, there is nothing to hold the water runoff, and it spends most of the day baking in the sun, except when it's shadowed by the cedar tree at the top which helps pull water and nutrients away from anything trying to grow. So, an excellent place for serious soil building, as well as a spot just aching for earthworks to better use the rain and snowmelt this spot currently just sheds. For reference, it's about 20 feet long, and six feet up the hill, at a slope of about 40 degrees.

Dead dead dead dirt.
So, we begin with the thinking and data collection. I already mapped out the basic landforms and local climate, and a shovel test keeps with expectations - the "soil" is a half-inch of dry crumbly stuff, on top of clayey stuff underneath. Unlike much of the yard, this doesn't show signs of having been loved and utilized at length in the past, it just looks like crappy, paper-thin yard dirt. My plan, therefore, is to build up hugelkultur mounds to start building organic depth in the soil (and building something deserving the name "soil"), while also shaping the mounds to act as runoff-blocking ridges. The ridges create small swales (low lying, moist areas) behind them, and the swale's water will be soaked up by the mounds, as their wood innards can absorb, and will need initially, large amounts of water to "charge". Careful shaping of the mounds also ensures proper runoff channels in case of torrential rains. So, goals here:
  1. Build soil
  2. Catch & utilize runoff
  3. Minimal financial investment
  4. Don't abuse landlord's amazing willingness to let me dig up the yard
Goal #4, in particular, dictates digging down more than piling up, so that the height of the mounds will be less obvious, less obtrusive, and less likely to get immediately bulldozed as soon as we move out. My next post will start, therefore, with the digging of graves trenches.

No comments:

Post a Comment