raised bed. Adopted by permaculture advocates, the technique helps to improve soil fertility, water retention, and soil warming, thus benefitting plants grown on or near such mounds.[1][2]
History
Hügelkultur is a German word meaning mound culture or hill culture.[3] Though the technique is alleged to have been practiced in German and Eastern European societies for hundreds of years,[1][4] the term was first published in a 1962 German gardening booklet by Herrman Andrä.[5] Inspired by the diversity of plants growing in a pile of woody debris in his grandmother's garden, Andrä promoted "mound culture" as opposed to "flatland culture".[5] This was also posited as an easy way to utilise woody debris without burning, which was illegal.[5] Andrä appears to have been influenced by Rudolf Steiner's biodynamic agriculture. Steiner explained his biodynamic philosophy as developed through meditation and clairvoyance, on the grounds that his methods were “true and correct unto themselves.”[6] Andrä quotes a 1924 lecture on biodynamics by Steiner, which describes mixing of soil with composting or decaying material in earthen hillocks.[5] 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.[5][7]
The technique was later adopted and developed by Sepp Holzer, an Austrian permaculture advocate.[8] More recent permaculture advocates such as Paul Wheaton strongly promote Hügelkultur beds as a perfect permaculture design.[9]
Use
Construction
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. (Note—Wheaton suggests piling the wood higglety-pigletty rather than in a neat stack as shown, for structural engineering of the steep slope, or perpendicular to the spine of the mound.) The sides of the two slopes both have a grade of between 65 and 80 degrees.[10] The beds are usually about 3 by 6 feet (0.91 by 1.83 m) in area and about 3 feet (0.91 m) high.[1] However, this height reduces as decomposition progresses.[5]
When positioned on sloped terrain, the beds need to be placed on contour, or 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.[11][12] Mounds may also be made from alternating layers of wood, sod,[13] compost, straw, and soil. Although their construction is straightforward, planning is necessary to prevent steep slopes that would result in erosion.[8][4]
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.[10]
Planting
The mound is left to rest for several months before planting,[5] although some advise immediate planting.[citation needed]
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, zucchini, 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.[citation needed]
Lifespan
The original German publications described the mounds as having a lifespan of 5–6 years, after which they had to be rebuilt from scratch.[5]
Evidence
As of 2017 there are no peer-reviewed scientific studies available regarding the efficacy of the technique.[5] A few university student projects investigate Hügelkultur but have not been published in scientific journals.[5]
One small scale and short term student project investigated the Hügelkultur method as a potential use for yard trimmings waste, and also if lima beans, kale and okra planted on a Hügelkultur 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.[14] 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.[14] 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.[14]
A student thesis investigated the water holding capacity of Hügelkultur beds and whether the technique could be useful to prevent karst rocky desertification in China.[15] Over 3 months of measurements, water concentration in hügel mounds remained high. Samples from hügel sites contained almost twice as much water as those from flat control plots. It was suggested that 1 ha (2+1⁄2 acres) of hügels has 3-10 times more water than a flat plot affected by karst rocky desertification.[15]