by Dan Hughes
Hügelkultur, translated literally from german, means ‘mound culture.’ More specifically, it is the use of rotted wood and other organic materials to create low-input raised beds that are highly water retentive and self-feeding. It is a method that is based on the simple principles of decomposition that, when done properly, provides nutrients to the plants without the need to add externally acquired fertilizers for years while at the same time holding what water they receive for extended periods. They are therefore well suited to dry climates and production in areas where fertilizers are not desired, aren’t accessible or are prohibitively expensive. In the following pages, I will demonstrate just how this method can be used in virtually any area to create permaculture beds that are essentially self sustaining indefinitely with the proper care and cultivation.
Hugelkultur beds are little different from other raised beds in composition apart from one key difference: the beds are built on top of a stockpile of rotted wood and other composting biomass, be it duff, leaves, wood chips or whatever else may be on hand. Because of the large mass of all this, the beds will necessarily be built high and so are most often the site for the bed is dug out a few feet. The depth to which the troughs are dug is determined by preference, the amount of time and effort one is willing to spend in building the bed (though this part is obviously greatly facilitated by the aid of heavy digging equipment), how hard the soil is and so on. For example, were you to want to make a hugelkultur bed in a neighborhood where there are restrictions regarding the appearance of a yard, it is possible to make the bed rise only a foot off the ground when in reality it may reach as far down as six feet. Most sources recommend a total height of at least four feet and ideally around six feet when the beds are completed, especially since much of this height will be lost in the first couple of years as the organic materials break down and thus compact slightly. If appearance is not an issue or there is only a limited amount of wood and organic materials available, it is perfectly suitable to simply build your beds on top of the existing ground level although you will then have to import soil from elsewhere. Typically the troughs are dug to a depth of about two to three feet with the soil and sod set aside separately, filled in with the rotted wood and other biomass, covered with the turf inverted so the soil side is up and then covered again with the remaining soil. After this, the beds are ready to be planted; indeed, as we will see later, there is good cause to plant the beds immediately.
The process that makes hugelkultur work is no mystery. The key is the stockpile of organic material created underneath the bed. According to Sepp Holzer, the preeminent authority on all matters permaculture, the wood acts as a sponge, holding in what water falls on the bed as well as drawing moisture up from the ground. As the wood decomposes its nutrients are fed directly into the soil of the bed while simultaneously providing food for microbes and nematodes (2011). Paul Wheaton of Richsoil.com states that the shrinking that occurs as the wood breaks down will, over time, create air pockets that promote strong root growth and loosen the soil which makes tillage all but unnecessary (Wheaton, n.d.).
One of the best attributes of hugelkultur is its versatility. It is possible to use a huge variety of materials, locations, soil types and so on when making a hugelkutlur bed. There are, however, a few considerations that should always be made before building one. Location is the first and foremost of these. One should take several factors into account when choosing a site for the bed. Sunlight, as always, is the foremost of these, and as such the beds should be oriented to maximize sunlight throughout the day. A bed that runs north to south would create an optimal conditions for most plants, but if you wished to grow plants that needed indirect light, an east-west orientation would give you one side that received less light through the course of the day. Holzer also recommends that the prevailing wind direction be determined and a tall bed planted in tall, hardy plants such as berry bushes, jerusalem artichokes (Helianthus tuberosus), or even fruit trees to create a windbreak, thus preventing soil compaction in other beds from constant wind (2011). Slope is another important consideration, and if the beds are to be built on a sloping surface it is perhaps the most crucial. This is because the beds are so absorptive that if they are not oriented properly with the flow of water, they will become over saturated. According to Holzer, beds should be neither parallel nor perpendicular to the slope of the hill but rather “…determined by the course the rainwater takes down the slope” (2011). Were your beds to run perpendicular to the slope then those at the top would catch all the water, leaving those at the bottom deprived and dry. If the opposite orientation is employed, the water would simply sheet down the hill which could lead to massive soil sloughing and even landslides. Therefore, what Holzer is suggesting is that you take note of which way the water flows and then position the beds on a slight bias to the slope with offset breaks between them. This way the water will flow down along the sides of the bed allowing them to absorb some but all until it reaches the end of the bed and then passes through the break, down to the next row of beds, thus evenly distributing the water between all beds while slowing its roll down the hill. Accessibility is another factor worth going into. The placement of your beds should be in an area that is easily reached and that can accommodate the desired length and height of your beds with plenty of room between them and on the ends to facilitate plantings and harvests.
Once you’ve chosen the appropriate location for your beds, it’s time to start digging. It should be noted here that it is not entirely necessary to dig out trenches for your beds, but it is highly recommended for a couple of reasons. Firstly, digging will create a stockpile of soil that would otherwise have to be brought in from elsewhere. Secondly, digging troughs will create beds that are of a shorter final height. Due to the nature of hugelkultur, the more organic material that is buried in the bed, the better it will perform over a longer period of time. Wheaton suggests beds that are at least six feet (2m) in total height (Wheaton, n.d.), but the above ground height will ultimately be determined by the depth to which your trenches are dug. For example, if you wanted to create beds that are a total of six foot (2m) but only rose above the ground three feet (1m), then you would want to dig down 3 feet (1m). It is in this way that huglekultur can be made to conform to neighborhood restrictions or personal preference. The beds can, of course, be shorter, as any amount of buried organic material and wood will aid in the growth of the bed. However, the greater the percentage of the bed that is buried the less arable surface area present in the bed. That is why Holzer, Wheaton and others suggest that you dig 1 1/2 – 2 feet out and build up to a height of 4 1/2 – 4 foot above ground, totaling 6 feet (2011, n,d.). Using heavy machinery for digging and moving the rotted wood, soil and other organic material will obviously speed up the process but it is not necessary, especially for smaller beds.
After the troughs have been dug, you can start filling them in with the rotted wood. Wheaton posits that it is important to use wood that has been rotting for at least a year primarily because if freshly cut wood is used, it will rob much needed from the soil as it decomposes. Therefore, the more rotted the wood, the better as this will not only prevent nitrogen robbing but will also essentially inoculate your bed with microbes, fungus and bacteria needed for the decomposition process that makes the whole thing work so well (n.d.) One must also put thought into the types of wood that are used, as certain species are well suited to the task while others must be avoided due to their negative (for this application at least) attributes. Cedar, ailanthus black walnut are no good because they are allelopathic (meaning that they produce biochemicals that can negatively effect the growth of other plants). Locust is far too rot-resistant to be effective. The best woods for hugelkultur, according to Wheaton, include but are not limited to: alders, applewood, cottonwood, poplar, maple and birch (n.d.). Conventional wisdom would have it that the harder/denser the wood, the worse it is for this purpose as it would be slow to break down, and indeed there is a good deal of debate on this matter on the internet with some purporting that the slower the wood breaks down, the longer the bed lasts and others saying that this slower breakdown will negate the reason for using the wood in the first place. For the purposes of this article, I will advise that you should use what is most readily available to you without using species like the ones listed above that will retard the growth of your plants. There are myriad considerations to be made here (acidity levels in the soil and wood, allelopathic properties, whether or not the pieces of wood will create new growth, etc.) and each region is different in an equally large amount of ways, namely in species diversity. So ask around, do a little research and find out which woods will be best suited to your climate, soil type, what species of trees are abundant in your area, the types of plants you want to grow in the beds and so on. The beauty of hugelkultur is its adaptability. You don’t actually have to use wood at all, though your beds will be substantially more effective if you do.
It is advisable to lay some of your rotted wood in vertically, as this will aid in wicking moisture upward to your plants. Additionally, I never think that it’s a bad idea to inoculate any type of bed with effective microorganisms, mycorrhizae, or some of the various beneficial worm species. The wood should be mounded neatly and tightly but not without gaps and spaces for dirt to fill in. Holzer maintains that beds should be tall and angled at least 45 degrees as flatter beds will over time become compacted and “…the process of decomposition is interrupted and … an anaerobic sludge can build up, which has a negative effect on plants.” He further suggests that you can slightly terrace the sides of such steeply angled beds to ease planting and harvesting (2011). Once this is done, you can cover your wood with any excess organic material you may have on hand such as leaves, wood chips, straw, manure or compost. After the innards of the beds are built, you are ready to apply the final layers. If the area that was dug out had grass or turf, most people advise that you put it on with the grass side down to create structure and add to the organic material available for decomposition. On top of this you make a final layer with the dirt that came from digging the troughs. Wheaton suggests that the best soil be separated from the rest to be used on the outermost layer, or you can apply whatever amendments you may have on hand to improve the quality of the soil (n.d.). As you pile the dirt on that you water it so that it will hold its shape better. Once all this is done, you are ready to start planting.
Holzer, among others, stress the importance of being ready to plant as soon as you are finished building the beds. This is because the soil will still be loose, aiding in quick root growth and helping to prevent seeds from blowing away in the wind or washing out with rain, and as such, you should not overly smooth the surface of the beds in order to preserve these optimal conditions (2011). When choosing what plants to put in your beds, there are again many things to take into account. The first of these of course is the climactic restrictions of your region. For the most part, you will grow the same plants in a hugelkultur bed as you might in any other bed. It will be possible, however, to grow plants that require more water than if they were to be planted in the ground. This is because of the incredible absorptive powers of the wood and organic materials in hugelkutlur beds. Not only will they hold water for longer periods of time than other beds, but they will actually hold more, thus enabling you to grow plants that might not otherwise be feasible in your region without massive irrigation (Holzer, 2011). Wheaton also claims that the warming of the beds in the initial few years actually enable you to extend your growing season as the soil will be warmed from within (n.d.). Though the choice in plants ultimately comes down to what you wish to grow, as with any permaculture scenario it is always to have a well thought out and diverse array of species that will complement one another in their growth. It is also important to think about planting deep rooted perennials for two reasons: one because they will add to the overall structural soundness of the bed but also because their long roots will draw moisture up to the benefit of other, shallower rooted plants. Another important factor to bear in mind is decomposition level of the organic material used in the bed previous to building. If your materials are small and only slightly composted, then you can expect high levels of nutrient release in the first few seasons and so you should plant accordingly with high demand plants such as cucurbits, night shades, and apiaceae (Holzer, 2011). You can then move on to less demanding plants like legumes (even better as they will fix nitrogen and add to the fertility of the bed) in later years. Mulch crops are also recommendable, and these again will be determined by all of the factors stated above. Strawberries are a good example, as they spread easily, are good for shading out the ground beneath, are hardy enough to be cut back to make room for planting and have the added value of producing an edible fruit. It will also be to your advantage to plant a resilient cover in the aisles between your beds; something that can withstand foot traffic but at the same time keep the soil in place.
Again, the best part of hugelkultur is how open-ended it is at every turn. As long as the basic principles are in place, then chances are your beds will flourish. Hugelkultur may afford those who have little water a viable option for growing much more than they could without the massive water storage capacity of the wood. It also creates an excellent use for wood and other biomass that might simply go to waste otherwise. If nothing else, it provides an interesting experiment that is a great alternative to normal raised bed gardening. This article really only scratches the surface of possibilities regarding hugelkultur. Its applications and variations are seemingly endless, they need only be implemented and, of course, shared with the world.
For more information, refer to the cited materials as well as the many on-farm trials and blogs that abound on the internet.
Wheaton, P. (n.d.). Hugelkultur: The ultimate raised garden beds. website: http://www.richsoil.com/hugelkultur/
Holzer, S. (2011). Sepp holzer’s permaculture: A practical guide to small-scale, integrative farming and gardening.Retrieved from http://www.krameterhof.at/pdf/presse/permaculture-pm68.pdf