Hügelkultur is a horticulturual technique where a mound constructed from decaying wood debris and other compostable biomass plant materials is later (or immediately) planted as a raised bed. Adopted by permaculture advocates, it is suggested the technique helps to improve soil fertility, water retention, and soil warming, thus benefiting plants grown on or near such mounds.
The term is first published in a 1962 German gardening booklet by Herrman Andrä. Inspired by observation of the diversity and success of plants growing in a pile of woody debris, "mound culture" is suggested (as opposed to "flatland culture"). This was also posited as an easy way to utilise woody debris without burning, which was illegal. Andrä appears to have been influenced by Rudolf Steiner's biodynamic agriculture. Steiner developed his biodynamic philosophy through meditation and clairvoyance, and rejected scientific inquiry on the grounds that his methods were “true and correct unto themselves.” Andrä quotes a 1924 lecture on biodynamics by Steiner, which describes mixing of soil with composting or decaying material in earthen hillocks. Joined by author Hans Beba, another German gardener, "Hill Culture - the horticultural method of the future" was revised and republished several times in the 1970s and 1980s.
The technique was later adopted and developed by Sepp Holzer, an Austrian permaculture advocate. More recent permaculture advocates such as Paul Wheaton and Geoff Lawton strongly promote Hügelkultur beds as a perfect permaculture design.
In its basic form, mounds are constructed by piling logs, branches, plant waste, compost and additional soil directly on the ground. The pile has the form of a pyramid. The sides of the two slopes both have a grade of between 65 and 80 degrees. The beds are usually about 3 feet (0.91 m) by 6 feet (1.8 m) in area and about 3 feet (0.91 m) high. However, this height reduces as decomposition progresses.
When positioned on sloped terrain, the beds need to be put at an angle to the hillside (rather than having them parallel to it). This makes sure the beds do not receive unequal amounts of water. In most cases, it is useful to have the beds positioned against the prevailing wind direction.
The raised bed can form light-duty swales, circles and mazes. Mounds may also be made from alternating layers of wood, sod, compost, straw, and soil. Although their construction is straightforward, planning is necessary to prevent steep slopes that would result in erosion.
In his book Desert or Paradise: Restoring Endangered Landscapes Using Water Management, Including Lake and Pond Construction, Holzer describes a method of constructing hügelkultur which incorporates rubbish such as cardboard, clothes and kitchen waste. He recommends building mounds that are 1 meter (3.3 ft) wide and any length. Mounds are built in a 0.7 meters (2.3 ft) trench in sandy soil, and without a trench if the ground is wet.
Anything can be grown on the raised beds, but if the bed will decompose/release its nutrients quickly (so long as it is not made of bulky materials like tree trunks), more demanding crops such as pumpkins, courgettes, cucumbers, cabbages, tomatoes, sweet corn, celery, or potatoes are grown in the first year, after which the bed is used for less demanding crops like beans, peas, and strawberries.
The original German publications described the mounds as having a lifespan of 5-6 years, after which they had to be rebuilt from scratch.
As of 2017 there are no peer-reviewed scientific studies available regarding the efficacy of the technique. A few university student projects investigate Hügelkultur but have not been published in scientific journals.
One small scale and short term student project investigated the hugelkultur method as a potential use for yard trimmings waste, and also if lima beans, kale and okra planted on a hugelkultur mound showed any signs of nutrient deficiency compared to a non-raised control bed. It was found that over 11 tons of yard trimmings were used in the mound, and no evidence of macronutrient deficiency could be detected in the crops in the short term. Indeed, despite concerns that incorporation of large quantities of high carbon woody matter would lead to nitrogen immobilization and hence nitrogen deficiency in the crop, a higher level of nitrogen was found in the raised bed. However the micronutrient iron was lower relative to the control bed. The author speculated that no nitrogen deficiency occurred since the roots of the plants did not penetrate past the superficial layers of the mound into the deeper wood-containing region.
A student thesis investigated the water holding capacity of Hugelkultur beds and whether the technique could be useful to prevent karst rocky desertification in China. Over 3 months of measurements, water concentration in hugel mounds remained high. Samples from hugel sites contained almost twice as much water as those from flat control plots. It was suggested that 1 Hectare of hugels has 3-10 times more water than a flat plot affected by karst rocky desertification.
Many publications and websites advocate the technique based on personal experience of the authors. Some have criticised the technique as lacking genuine scientific principles, and running counter to the ecological principles of soil building with litterfall.
Hügelkultur is said to replicate the natural process of decomposition that occurs on forest floors, however in natural ecosystems wood would be present at the soil surface. Trees that fall in a forest often become nurse logs decaying and providing ecological facilitation to seedlings. As the wood decays, its porosity increases, allowing it to store water like a sponge. The water is slowly released back into the environment, benefiting nearby plants.
Hügelkultur beds are said to be ideal for areas where the underlying soil is of poor quality or compacted. They tend to be easier to maintain due to their relative height above the ground.
Decomposition speed of organic material depends on the carbon to nitrogen ratio of the material, among other factors. Wood breaks down relatively slowly because it has one of the highest carbon to nitrogen ratios of all organic matter that is used in composting. If the wood is not processed into smaller pieces with larger surface area to speed up chemical reactions, breakdown is even slower. The decomposition process may in the short term take more nitrogen from the soil through microbial activity (nitrogen immobilization), if not enough nitrogen is available. Thus in the short term the fertility of the soil may be decreased before eventually, perhaps after 1-2 years, the nitrogen level is increased past the original level. Traditionally therefore, it is said to be advantageous to balance "browns" (e.g. woodchippings) with "greens" (e.g. leaves) for efficient compositing, and to allow compost to become well-rotted before applying it a bed to prevent competition between soil bacteria and plants for nitrogen, reducing yield.
Criticisms and controversy
Hügelkultur mounds as solid earthworks
Although hügelkulture beds can safely retain water in light-duty applications (for example, conserving the moisture of rain that falls on the bed), creating heavy-duty rainwater retention areas behind hügelkulture beds on contour, to catch surface runoff from surrounding areas, can be dangerous. Some designers conflate the hügelkultur bed's appearance with that of solid earthworks, but hügelkultur beds cannot predictably control large amounts of stormwater in the way that solid earthworks can. Whereas embankment dams or the hillsides of swales can be relied on to hold back many thousands of gallons of water for weeks to allow it to seep into the ground, and berms can slow runoff, hügelkultur beds are different in two ways: earthworks have no buoyant core (whereas hügelkultur mounds contain logs), and the soil that they are made of is compacted. If fresh or dried timber is used in the bed, it may become buoyant in the water-saturated substrate, bursting from the soil covering and releasing all the sitting water through a breach. This can be an issue for years, until the wood is sufficiently rotten and infused with water. Another consideration is that hügelkultur beds will degrade, shrinking over time into much lower mounds of soft, rich soil. This means that the retention area will have less depth as time goes on, but it also means that the uncompacted soil will remain a threat to breaching even if the logs become saturated.
There is a recorded instance of a breach occurring in a new project. Upon the first rainstorm, the retention areas behind the hügelkultur beds filled with water and broke through. The released water carried the freshly-buried logs and dirt downhill, smashing a hole in a building being used as a church and filling the space with mud. No injuries were reported.
Some permaculturists have taken mild positions against the "hügel swales" still being promoted by other permaculturists, citing the danger and cross-purposes of hügelkultur beds and swales.
Overfertilization, contamination of soil and water habitats
Over-fertilized plants are said to have less flavor, and too much nitrogen can be consumed by eating certain plants which have been over-fertilised (e.g. spinach). Advocates state that overfertilization is a risk in the first year if woodchips are used, which will break down too fast. Instead raised beds made with whole logs release nutrients slowly over a period of years. It has been suggested that excessive use of decomposing organic matter in hügelkultur could leach out and contaminate and disrupt soil and water habitats.
- Miles, Melissa (August 3, 2010). "The Art and Science of Making a Hugelkultur Bed – Transforming Woody Debris into a Garden Resource". The Permaculture Research Institute. Retrieved May 2, 2014.
- "The Many Benefits of Hugelkultur". Permaculture Magazine. October 17, 2013. Retrieved May 2, 2014.
- Lauterbach, Margaret (February 2, 2012). "Margaret Lauterbach: Clippings fuel fertile 'hugel' mounds". Boise, ID. Idaho Statesman. Retrieved May 3, 2014.
- Martin, Claire (April 11, 2014). "Hugelkultur , translated: A path to richer soil". Denver, CO. Denver Post. Retrieved May 2, 2014.
- Chalker-Scott, Linda (August 2017). "Hugelkultur: What is it, and should it be used in home gardens?" (PDF). Pullman, Washington : Washington State University Extension. Retrieved 8 July 2018.
- Chalker-Scott, Linda (December 2013). "The Science Behind Biodynamic Preparations: A Literature Review". HortTechnology. 23 (6): 814–819.
- Beba, Hans; Andrä, Herrman. Hügelkultur – die Gartenbaumethode der Zukunft (10th ed.). Mannheim, Germany: Waerland.
- Palmer, Kim (August 14, 2013). "A Garden Made of WOOD; Hugelkultur (Hooogellocullocher or Hewogellocullocher) A Nature-Inspired Method of Gardening in Beds Built on Logs, Touted as a Drought-Resistant Way to Produce Food". Minneapolis, MN. Star Tribune. Retrieved May 2, 2014.
- Wheaton, Paul, hugelkultur: the ultimate raised garden beds, retrieved 6/9/2014
- Holzer, Sepp (2012). Hügelkultur. Chelsea Green Publishing. pp. 131–134, 139. ISBN 978-1603584647.
- Hemenway, Toby (2009). Gaia's Garden: A Guide to Home-Scale Permaculture. Chelsea Green Publishing. pp. 84–85. ISBN 9781603582230.
- Feineigle, Mark (January 4, 2012). "Hugelkultur: Composting Whole Trees With Ease". The Permaculture Research Institute. Retrieved May 2, 2014.
- Shein, Christopher (2013). The Vegetable Gardener's Guide to Permaculture: Creating an Edible Ecosystem. Timber Press. p. 28. ISBN 978-1604692709.
- Adams, A (May 2013). "UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM Student Project Report: Hugelkultur Gardening Technique Does not Result in Plant Nutrient Deficiencies and is a Potential Source Reduction Strategy for Yard Trimmings Wastes" (PDF).
- Laffoon, M (August 2016). "A Quantitative Analysis Of Hugelkultur And Its Potential Application On Karst Rocky Desertified Areas In China".
- Seymour, John (2008). The new self-sufficient gardener : the complete illustrated guide to planning, growing, storing and preserving your own garden produce (New ed.). London: Dorling Kindersley. pp. 12,13. ISBN 978-1405321334.
- Spirko, Jack (November 6, 2015). "Don't Try Building Hugel Swales". permaculturenews.org. Retrieved March 17, 2016.
- Holzer, Sepp (2011). Sepp Holzer's Permaculture: A Practical Guide to Small-Scale, Integrative Farming and Gardening. Chelsea Green Publishing. ISBN 9781603583831.