I am close to building three large hugel beds, but before I went digging I wanted to find out the actual science behind Hugelkultur.
So far I haven't been able to find anything - all the usual sources are bland - nothing on Arvix, Google Scholar etc. All I have found is a hard core permaculture guy saying that he can't find anything either and havingg second thoughts.
As far as it looks at the moment, Sepp Holtzer had the idea around 2006/2007, told people, those people told others... and so everything I have seen so far is either anecdotal or secondary evidence at best. I am much too lazy to dig out 13 cubic meters of soil without seeing some primary studies. I ***HAVE*** seen studies regarding guilds, mulching etc - and very positive they were as well ( which is why I'm using those methods now. Just can't find anything for Hugelkultur.
Can anyone point me at those that they have used or looked at, or let me know any universities currently undertaking studies who might share initial results or are publishing poster sessions?
I have never seen anything scholarly on the subject.
I live 8 miles from a university. I will let the right people know that they are welcome to check out my beds. I'm growing in mostly rock flour and rock. Most rain arrives in the winter. Things planted in the beds, survive. Things planted in just the native soil, die of drought.
I would not use this system if I were in good soil that gets summer rain.
"Mound Gardening" modalities have been recognised as a "no till" method of agriculture for a very long time, and I would credit Sepp for popularizing one of the more common methods. I can't find them at the moment, but I believe there is a paper from the 90's on this subject. It may be in German, so I would suggest doing searches in other languages other than English, as this may be fruitful. I will see if I can locate "hard copy" as there is still a great deal from the 70's through the 90's that have not been 'digitized' yet. Please do share what you may find.
You may have to search in Germany or Austria to locate any scientific data on Hugelkulture mounds. Here is a good place to start search the german web, you will, however need to speak Deutsch, most of the sites will not have an English translation.
Steve ... why dig? It's not all that much work to make a small bed.
Also, can't be that hard to find research in German / Austrian. Try a forum where members sort of idolize Sepp Holzer! There must be a FB page of his followers. Maybe Sepp has a FB page. Can't be so hard to find info in German / Austrian.
There have not been many true scientific papers published on hugelkulture in the USA, the above is however one of the best.
Most published information on the ancient method would be found in the 19th century and perhaps one or two from the 18th century.
The method was used by many cultures, Gauls, Celts, The east coast Nations of Turtle Island and Vikings.
The Native Americans built many growing mounds along the East Coast of Turtle Island (North America) most started their life as leftover depositories as evidenced by excavations where fragments of pottery, processed bones and wood fire ashes have been documented.
The usual method of building a mound is to start with a shallow hole in the ground, this is filled in layers with dirt put on as a cover between layers. Over time this "trash pit" becomes full of left over material, the dirt was used to contain odors as the pit filled up.
Once the pit was full, the site was continued to be used for depositing the refuse and the "mound" began to take shape. When it became necessary to start another pit, it was noticed that plants grew very well and with out the need of watering the mound.
This led to the use of the no longer used trash mound as a garden space. This was a common practice as far back as the 1400's and perhaps even further back in time. My elders tell several different versions of how we came to use mounds in the eastern nations.
The premise and practice of hugelkulture, as currently used, is an invention from the Franks and Gauls (now Germany/ Austria/ Poland) who used trenches filled with wood and covered with dirt as a way to hold water deep for plant roots to tap into.
The height of these mounds makes harvesting easier as well as increasing the quantity of food that can grow in a space. Decaying wood acts as a sponge, soaking up water and holding it until the roots of the plants draw the water from the wood.
This is not a method that works very well in extremely dry climates, nor does it work very well in extremely wet climates. It performs best in areas where there is at least 10" of rain fall or more.
A mound will change over the years, as the wood decays the mound will settle and different organisms will be present in the soil covering the decaying wood. Small mounds do not work as well as larger mounds, mostly because there is not enough material present to decay.
One of the ways I build my mounds to get them to work very well is to include bones, meat scraps, freshly cut grasses and other greens in the lower layers of the mound build.
I also do not leave air pockets as I layer up a mound. I do not start a build at ground level, I start with a trench, this trench determines the finished size of the mound since it is actually the base of the mound.
I use the largest wood at the bottom, fill in the cavities with smaller sticks then add a layer of green materials, any kitchen bones and scraps that will not be fed to our animals, then cover with a layer of the soil that was removed to create the trench.
I then build up, in thin layers, using what materials I've gathered or just add to the mound as I create new materials from the work on the farm.
Once I have decided the mound is high enough, I mix straw and dirt to use as the final cover, this goes on the top and as it dribbles down it forms the shape of the finished mound.
I don't try to make tall and narrow mounds, mine are more rounded with less steep sides at the start.
The steepness gets built as crops are grown and harvested, the mound settles and I add more dirt and straw/grass/etc. This allows the mound to be very stable, with little erosion since there are many roots holding the soil in place.
Cover crops and winter crops add to the root structures that hold the soil where it is and cover crops are chopped and left in place as mulch.
The real science of a mound is more hydrological than most people would think, it is more about building ground water than piling dirt.