Logs, branches, leaves, grass clippings, straw, manure, compost and other biomass available are layered in sections and topped with soil. Planting crops and ornamentals in such an environment benefit in many ways, the hills hold moisture, build fertility, and maximise surface volume in small spaces.
The gradual decay of wood and organic matter is a consistent source of long-term nutrients for the plants. A large Hugelkultur might give out a constant supply of nutrients for 20 years. The composting method generates heat which can extend growing seasons.
Soil aeration also increases over time as logs and vegetation break down, creating a long term low maintenance space free of constant cultivation. Acting like a sponge the Hugelkultur layers store rainwater and then release to the plants during drier times. There are currently trials of using Hugelkultur in deserts to use vital space for farming with positive results.
Once planting has established within a Hugelkultur, after a year of settling in, the water release in the mounds means very little watering is needed. It is also rich in wildlife, acting as a fantastic housing for all kinds of insects etc. Care must be taken to pack out mounds thoroughly as to avoid holes where larger, less required wildlife can take up residence! Mycorrhizal fungi working on the wood also develops in abundance. The wood has to be buried deep, though to avoid nitrogen lock-up. As wood breaks down, it robs nitrogen from the soil to aid decomposition; once broken down, it releases it again, but that is some time away and nearby plants may struggle to establish themselves without a helping hand. Maintaining hugels is mostly a question of appearance. If, as they break down they slump, you may want to top dress them with additional compost or mulch.
Some woods contain natural chemical agents that make them extremely slow to break down and tend to suppress plant growth so it worth avoiding Cedar,Black locust, Black cherry and Black walnut.
Any wood that is treated, including pressure-treated wood, railroad ties, pallets or painted/stained wood, should not be used. Clean, untreated construction or demolition scrap wood is still valuable.
Wood chips can be used too, but will result in a more homogenous hugel. This will burn nitrogen faster and not offer the same longevity of fertility that a classic hugel full of larger logs and timbers would.
Sepp Holzer the “rebel farmer” from Austria, one of the beacons of the perme culture movement is at the forefront of Hugelkultur building and develops them on a large scale up to 6ft height. A project recently in Michigan saw a community led by him build a 4km long Hugelkultur.
On such scale there has been criticism of its worthiness as vast soil quantities are needed to be moved which way have an effect on natural soil structure, erosion and flood levels etc. Care and critical analysis is needed on larger scale, commercial productions as these, but for small scale home gardens they are a wonderful way of creating a naturalistic topography which has positive long term sustainable effects on its environment.
Over time we would like to envision the Hugelkultur garden space re feeding itself. As current vegetation breaks down and dies, creating a constant cycle and environment to develop new planting over lifetimes where new and innovative planting types and food sources can be explored and gently cultivated.