Building Hügelkultur raised beds

August 22, 2013 in Permaculture by Claude

One of the first projects on the new land was to build hugelkultur raised garden beds, à la Sepp Holzer. Hügelbeet is German (generally spelled hugel-bed in English) and means hill-shaped garden bed, but specifically, it has come to mean wood-filled hill-shaped raised bed. Sepp Holzer has used these on a large scale in order to create micro-climates that allow him to grow all kinds of food in a climate that would otherwise be too cold to do so. Paul Wheaton is trying hard to spread the concept widely and the has a very neatly illustrated description of how hugelkultur is built and how they operate.

In a nutshell, the idea is to build a mound of wood and cover that with soil. The wood slowly decomposes and creates a rich soft spongy soil over time. One side-effect of this is that it reduces the need for irrigation. Another side-effect is that it creates a variety of different levels of moistness in the soil, with the tops being dryer than the lower parts of the beds, especially when they are built rather tall and steep. Depending on the shape and arrangement of the hugel-beds, they can create micro-climates by providing wind-shade or sun traps.

hugelkultur: hugelbed trench

With the micro-climates in mind, I began digging a trench about ten metres long and a good half metre wide and about one spade deep. That took a few evenings of digging. The point of digging the trench was to have some soil to cover the wood with. If you have a pile of soil lying round, you could save yourself the hassle of digging and just pile the wood straight onto the ground and cover it with the available soil. I didn’t have any extra soil at that point, so I dug the trench.

I designed the hugel-beds to be be curvy rather than straight in order to maximise different angles of sun exposure while minimising the north-facing part and avoiding any wind-tunnel effect. The picture above is looking more or less straight towards the north. The hugelbeds are on the eastern side of the big pond, sheltered somewhat from the prevailing western winds by bushes next to the pond. The bed winds its way from the south-east towards the north-west, perpendicular to the main wind direction and climbing up the very gentle slope  to allow cold air to escape downhill and not get trapped between the beds – the plan was to build two hugel-beds next to each other.

filling the hugelbed with wood

It is best to use waste wood, like brush or somewhat rotten wood for building hugelkultur, rather than bury timber or firewood. I had quite a pile of branches that I had collected since the previous autumn, and I ended up having to pollard an old willow that was in really poor shape, so I had some larger pieces of wood too. While I was building the first hugel-bed, the neighbours got interested in what I was doing. When I explained, one of my neighbours offered me a huge pile of half-rotten willow wood that they had lying in their yard and were more than happy to get rid of. I was more than happy to bury it in the second hugel-bed. :-) Talk about win-win.

It turns out to be much harder to stack twiggy branches into a trench than large logs. Whacking them with an axe didn’t really help much, so I chopped them in place with the chainsaw. That helped quite a bit to get a denser pile of wood. I then added the larger wood on top and sprinkled a good amount of organic fertiliser mix on it to provide some nitrogen to the mix. The wood takes up quite a bit of nitrogen during its decomposition, which it later releases to the plants again. It is therefore a good idea to include some extra nitrogen from the start, so as not to end up with a deficiency in the beginning.

filling the hugelbed with woodfilling the hugelbed with wood

The next step was to cover the whole thing with the soil I had dug up. It turns out, not entirely surprisingly, that when you spread the soil form a 30 cm deep and 5 cm wide trench over a pile of wood that’s about 60 cm tall (that means the wood pile is actually about 90 cm tall including the trench), that gives only a very thin layer of soil. I piled the sod I had dug up first, green face down, of course, and then covered the rest with the little soil available. I really would have needed more soil. Actually, I think it would have been better to add soil into the wood pile while building it, rather than trying to fill the gaps later. The lesson I learned here was that it takes much more soil than this, to build a hugelkultur properly.

hugelbeds covered with soilDSC_0348

I just about managed to build two of these beds before having to embark on a two-week work field trip to Lapland. When I returned the grass had turned from brown to knee-high green. By then it was already early June. I covered the beds with a thin layer of compost (I would have put a thicker layer if I had had more compost) and I sowed a variety of vegetables in them to create a nice polyculture: mostly peas and beans to fix more nitrogen into the soil, but I also tried some tomatoes, some heirloom spinach, soup sorrel and around the bottom edge, potatoes. A neighbour gave me some gherkin seedlings, so I added those too. After a few days, I notices some really strange looking bright yellow slime mold swarms spreading out over the top of the hugelkultur beds. I guess that’s a good indicator that the microbial and fungal activity was getting off to a good start.

vegetables growing on hugelkultur in cold climate

By the end of the summer the beds were covered partially in vegetables and partially in grass and weed. The grass from the sod layer came through in many places, despite turning it upside down. The gherkins did best, probably because I got them as seedlings and the rest of the vegetables were sown too late in the summer. The growing season is short here, so being a week late with sowing can make a big difference, let alone two weeks. The potatoes also seemed to like the bottom of the hugel-beds, so there were some successes. In order to get better results, I really need to add a thicker layer of soil and compost for the next season.

The micro-climates seem to work, at least in the way of soil moisture variability. I need to have a closer look at temperature differentials during the next growing season. I think it might be interesting to observe  where the warm spots are, particularly in the early part of spring. Time will tell how this works out. Hugelkultur beds are said to take a few years to exhibit their full potential.