Hugelkultur is a form of raised bed gardening using layers of organic material. We previously discussed keyhole gardening on the blog, and hugelkultur gardening has a few similarities. It has become a popular technique in permaculture circles. Broadly speaking, permaculture is an approach that emphasises working with nature as much as possible and gardening in a sustainable way.
The word hugelkultur roughly translates from German as ‘mound culture’. The term itself originated in a German gardening booklet in the 60s. Hugelkultur beds have a mounded shape (unsurprisingly) with sloped sides. The mound can be as high as 6 feet and is built up with a number of layers that consist of different kinds of organic material. Many people adopt a variation on this mound technique that involves digging a trench and placing the lower layers into this trench. The result is a lower-lying bed that nonetheless follows much the same principle.
When it comes to building the layers of a hugelkultur bed - and how many layers to include - there seems to be a fair bit of variation at play. Some sources will recommend as many as 7 layers while others will say four or five. (Seriously, I don’t think I’ve seen two diagrams that look the same on this subject.) We’re not going to provide an exhaustive list of layer contents one-by-one here because it really seems to depend on the individual, and maybe even more importantly how much material you have to hand.
This is maybe one of the most distinct characteristics of the hugelkultur bed. The lowest layer is where you place partially rotted logs, thick branches and other wooden material. This forms the structural core of the bed/mound, and the idea is that this material will break down very slowly over a period of years, as well as providing sponge-like moisture retention.
Hardwoods will take longer than softwoods to break down, and add to the bed’s longevity. Softwoods on the other hand will offer better water retention but break down faster. It’s important not to use treated wood which can leech harmful chemicals.
Next Layers Up:
The contents of the next layers up aren’t as clear-cut, and can differ depending on what you have available. Generally they should consist of material like smaller branches, twigs, fallen leaves and cut leaves or grass cuttings. This is said to act as a barrier between the log layer and upper layers, as well as providing more moisture. When placed higher up in the ‘mound’, smaller forms of organic matter can provide nutrients as they break down. Gaps between this material will contribute to aeration within the mound.
Second From Top Layer:
Partially rotted organic material, or manure that has not fully broken down yet, as well as kitchen scraps. This layer should theoretically add a lot of warmth as well as nutrients, due to the natural levels of heat as material continues to break down and decompose. In effect, the mound has its own inner compost heap.
Your top layer should consist of finished compost and topsoil. This should be thought of as your growing medium, the same way as the top layer of any raised bed set-up. It’s important for the top layer to be fairly thick with reasonable depth, as you don’t want the plant roots to be reaching down into the ‘manure’ layer too early (which can burn young roots). The upper portion of your bed can also encompass a ‘mulch layer’ to further optimise plant growth.
Advantages of Hugelkultur Gardening
As can sometimes be the case with gardening techniques, there’s been debate as to whether hugelkultur has actual practical benefits for most growers or whether it’s perhaps been hyped up a little. Some of the touted benefits of a hugelkultur raised bed include:
- good moisture retention
- improved soil fertility
- the ability to warm up faster at the beginning of the growing season
- they’re long-lasting
- They can require less long-term use of fertilisers and inputs due to the self-sustaining layers
A lot of these benefits are hard to prove with any certainty and are mostly based on anecdotal success. Not that there’s anything ‘wrong’ with anecdotal accounts. The layering of the mound structure does make a certain sense when you look at it on paper, but in practice it may not work out that way. If this sounds like a fun experiment to try out in the garden, by all means go for it - but it may not be particularly successful in moderate climates like we have in Ireland and the UK.
Things to Keep In Mind
You will need a fair amount of wood and timber material to layer up the base of the hugelkultur bed. If you have a lot of material to get rid of then this is one way to put it to good use, rather than disposing of it or burning it. In comparison to growing in a raised bed it can also reduce the amount of soil that you need to use to build up your bed - so if you have the material to hand it can be a somewhat budget-friendly method.
On the other hand, if you don’t have a lot of this material just lying around then trying to create one of these beds might be more trouble than it's worth. You will ideally need a mix of both hardwoods and softwoods, which can be a big ask of the average gardener.
The high mound construction of a hugelkultur bed can create a situation where one side of the mound won’t be receiving as much sun and may instead be in shade. While this might be something you can make work for you, it can also quite likely create problems. The mound structure can also cause undesirable runoff when it rains.
It’s sometimes recommended not to plant in the hugelkultur bed straight away if there is organic material such as manure still breaking down in the upper layers. On the other hand, leaving it for a few months before planting means that some of the touted benefits of the hugelkultur bed (heat from material breaking down) no longer seem as clear-cut.
Bear in mind that even if you’re not convinced of the benefits of a hugelkultur bed (or its suitability for your own circumstances), some of the principles of hugelkultur can still be used in your garden. For example, you can use partially decomposed woody material to layer up the base of new raised beds and potentially improve their water retention.