Although the term ‘hugelkultur’ (hill cultivation) was not used by Sepp Holzer, he advocated the idea of using logs, brush or other high carbon garden waste to grow crops on. The top soil is first removed and the logs placed in the trough left where the soil was. The soil is then replaced over the biomass (upside down if turf) and crops are planted into the top soil.
The rotting wood under the crops acts as a sponge, soaking up any excess water and preventing the soil from drying up in dry conditions.
Hugelkultur has the benefit that crops need less irrigation, the rotting wood has the effect of holding onto water.
As the wood decomposes a gentle heat is given off to the soil above.
Crops grown on hugelbeds taste better and are thought to be more nutritious than those grown in soil. This may be because the rotting wood encourages fungal activity, some of which may be symbiotic.
Terraced Polytunnel Hugelbeds
We have taken hugelkultur one step further and have created terraced hugelbeds in our polytunnels. These can be made from old pallets or planks of wood.
Or they can be made out of old plastic flower buckets with the bottom of the bucket cut off to allow roots to grow into the hugelbed
Or plastic crates
Or traditional Welsh cut roofing slates for a delux version
There are many benefits of making terraced polytunnel hugelkultur raised beds:
They increase the surface area of the beds, allowing more rows of crops in a limited space. The photo of the wooden pallet terraces shows 11 rows of crops where only 4 rows at the most would fit on level ground. Polytunnel space is valuable, the plastic covers are not cheap and do not last for ever. With these raised beds it is possible to fit nearly 3 times more crops into the same area without using plant containers which are not directly connected to the Earth.
They clearly define paths, stopping people from walking on the growing beds.
They gently give off heat as the wood decomposes, enabling a longer growing season.
Hugelbeds require less irrigation than soil beds as the decomposing wood has a sponge like effect, absorbing and retaining water.
They are easy and cheap to make from a variety of second hand or recycled materials.
When creating a hugel bed, you are making a hill. When it rains, soil moves down hill. Terraces capture and hold soil, causing it to build up behind the terrace wall rather than be lost from the hill.
Stabilise that Carbon.
One limitation with Hugelbeds is that the carbon in the logs is not always made stable; as the wood decomposes the carbon is released back into the atmosphere as CO2.
The rate and extent of decomposition will vary with different soil microbial populations. In warm, humid climates the microbial communities will decompose the wood more rapidly. This is why, despite large amounts of carbon being drawn down by the massive trees of the Amazon forests, the soil is generally very shallow and fragile.
Wood in wetland ecosystems is more stable because aerobic bacterial decomposition is inhibited. Peat bogs for example form in wet systems but a peat bog will rapidly decompose once it has been drained.
This is important because it is common practice in permaculture to locate hugel beds in the berm (the lower side) of a swale where, if condtions are right, the water in the swale will help to stabilise the carbon in the hugelbed.
We have been adding biochar to hugelbeds in the hope that this will mimic some of the conditions under which tera preta was formed in the Amazon. It is hoped that the biochar, which is a byproduct of our stove and heating systems, will be instrumental in producing a net gain in stable carbon in the beds and that nutrients will not be washed away as the beds are irrigated.