PWP Leads Innovation in Building Healthy Soil

Pasadena Water and Power is piloting a centuries-old, European horticultural technique - Hügelkultur - for its ability to reduce or eliminate irrigation in municipal landscape settings. PWP was awarded a grant from the Bureau of Reclamation to build hügels at several City sites and educate residents how we can use a nature based technology to build healthy soil and save water in our landscapes.

What is Hügelkultur?

Hügelkultur is a no-dig technique that utilizes both fresh and decaying logs, debris and other compostable biomass in a raised and mounded bed on which plants, trees, and shrubs can be planted. Hügelkultur needs whole trunk wood with bark in order to be most effective, as the logs decompose slowly and steadily, rather than all at once (which is what happens if you only use smaller biomass like twigs and bark chips).

Hügelkultur mimics natural woodland and floodplain processes where woody debris and other biomass falls to the ground, over time becomes sponge-like—soaking up rainfall and slowly releasing moisture, nutrients and fostering biodiversity in the surrounding soil—and thus making the moisture and life supporting processes available to the surrounding flora.

Of interest to PWP is Hügelkultur’s ability to retain significant amounts of moisture. Moisture retention is accomplished through four complementary processes:

  1. Rainwater capture. The mounded hügels have increased surface area to capture more rainwater. Capture can be maximized with the concurrent usage of bioswales and berms to channel and infiltrate rainwater.
  2. The hügel’s “sponge.” The slowly decomposing biomass in the hügel acts as a sponge that retains water over a long period of time.
  3. Ongoing condensation occurs due to the temperature differential created by the thermal mass of dense logs within the hügel and the moisture bearing night air.
  4. Hügels are an ideal medium in which mycorrhizal fungi can flourish, infiltrating the entire bed of piled logs, converting their carbon into nourishment for plants growing above, and distributing moisture horizontally to the plants and trees surrounding the hügel.

These processes, especially the proliferation of mycorrhizae, significantly improve soil health, further contributing to hügels’ ability to produce robust plants, shrubs, trees, and landscape with minimal (or no) irrigation and to thrive when planted with native plants.

Local Examples

One of the hügels at Sheldon Reservoir Landscape.

PWP has completed two hügels at the Sheldon Reservoir Landscape, at the corner of Coniston Road and Arroyo Boulevard.  The next site for hügels will be in the Arroyo Seco adjacent to the Gabrielino Trail.  Following will be the implementation of hügels at the northern end of the Sierra Madre median.

(Left) A local resident's hügel in their front yard; (Right) A hügel featured on Urban Homestead's property.

Check out this video of the building of Hügels at Sheldon Reservoir!