Hugelkultures: the raised bed of Permaculture

As most readers of this site already know, Permaculture mimics creation, copying the work of God, the greatest designer. Here are two more natural patterns for us to follow.

In old forests, rotting, mossy logs slowly crumbling into the earth are a common sight. Small trees often root right on top of them, and surrounding vegetation and fungi tap them for water. Even late in a dry summer, rotting wood is still moist. They also trap soil, keeping it from sliding away, and nurture a vast community of beneficial life. Rotten logs enabled the ecosystem of Mount Saint Helens to quickly rebound after lava flows and mudslides.

Old growth forests tend to have a pit and mound topography. This is caused as large trees fall, turning up their root balls. They then rot away, leaving a mound of rich, well drained topsoil and crumbly wood, and a moist, shady pit with mineral subsoil exposed at the bottom. Both pit and mound have a sunny side and a shady side. This diversity of terrain creates a diversity of wildflowers on the forest floor, as many as fourteen species to the square yard. The diversity of plants then promotes a diversity of insects and a more stable system.

We can mimic these two patterns by building a hugelkulture. To build one, a shallow trench is dug, and the topsoil and sod are set aside. Then a mound of woody debris; brush, logs, rotten firewood, etc. is piled into the hole or trench. Manure, straw and other organic matter is placed on top, and then the soil is placed over all. They can be built in any shape, but are generally formed in long ridges, between three and seven feet high, running east-west, so that they each have on North and one South face.

The advantages are numerous.

  • The mounded shape is able to fit in more plants than a flat bed with a similar footprint would be able to do, effectively increasing surface area. (This is imitating another natural principle; in creation, surface area is often maximized to utilize resources, in this case garden space, effectively. The human lungs have an interior surface area the size of a basketball court.
  •  The spaces between the sticks, and the raised position of the bed, insure well aerated soil, and prevent flooding damage to crops.
  •  The rotting sticks hold a huge volume of water, so the plant’s roots can always access sufficient quantities of both water and air.
  •  The wood holds on to nutrients and keeps them from leaching away.
  •  The decay process provides a gentle heat which stimulates plant growth.
  •  This strategy maximizes organic matter.
  •  The wood feeds fungi and other beneficial organisms, which are often lacking in traditional gardens.
  •  The south face warms up early and has a much warmer microclimate then the surrounding area. This allows production of crops which need a lot of heat, and are typically difficult to grow in Colorado, such as melons and sweet potatoes. At the same time, the north side stays cool and shady, and helps lettuce and similar crops avoid bolting in the heat of summer. (This is similar to the diversity of wildflowers mentioned above.)
  •  If laid on contour, the hugelkultures catch water running down a slope.

We will be building a number of hugelkultures, both in the annual vegetable gardens and in the orchards.