The word Hugelkultur (pronounced HOO-gul-culture) is taken from the German word for “hill” or “mound,” and means “hill culture.” It is a centuries-old composting method that has been developed and practiced by many permaculture proponents as a way of making raised garden beds filled with rotting wood, mulch, and compost. Hugelkultur beds can be used to grow a typical garden without irrigation or fertilization that lasts for years, making it a wonderful method of growing food in a very limited space. Hugelkultur is highly valued for its benefits in farming at large and small scales, and is noted for its ability to decompose organic materials, and provide sustainable, long term composting.
Hugelkultur has many benefits for both large and small scale gardening, and has been demonstrated to work in many environments and conditions, ranging from huge, open deserts, down to the minute scales of a backyard. It’s perfect for places that have had trees blown over by storms, is useful on terraces and hillsides, and can even be built on contours to create a Hugel-swale system that fertilizes and waters itself automatically, helping to retain moisture for longer. It’s also good in areas that have shorter growing seasons, or have poor soil qualities and low moisture content. The reason for this is because, for the first few years or so, as the wood and organic materials in the bed decompose, they will break down, release energy, and generate heat, all while fertilizing the soil and retaining water. This water, energy, and heat will feed the plants and warm the bed, which will help stimulate root growth, help living organisms propagate in the bed, and extend the growing season for the plants.
Using Hugelkultur is also environmentally friendly, and, combined with other permaculture-style practices, it makes for a great way to recycle used food scraps, cardboard, biodegradable garbage, and old wood and woody debris, including branches, twigs, logs, or even whole trees. This can transform a pile of junk and wood into a productive resource, saving it from being turned into waste or pollution. This wood can also be locally sourced, so you don’t have to import any of it from outside, cutting costs on time and resources, and contributing to attaining sustainable production. Furthermore, you can even recycle kitchen and garden waste with your beds, in addition to using grey water, serving as an easy source of food and water for your plants, further adding to Hugelkultur’s sustainability value.
Hugelkultur is also easier than traditional gardening, because the increased height of the bed makes gardening take less work, since you don’t have to bend down as much. And, although it takes more work to set up, Hugelkultur makes for less work over time. This is because, after the first or second year, all irrigation and fertilization will be done naturally, reducing work and maintenance for yourself even further. And, when combined with other permaculture and polyculture techniques, you can eventually eliminate the need for planting seeds, as the plants will thrive and reproduce on their own, resulting in crops that are miles ahead of those grown with standard practices. The flavors of the plants will also be made stronger, especially for fruits.
Benefits and Uses
Hugelkultur beds have many advantages, and are useful for a wide range of functions, including: waste and systems management, recycling food waste; composting spare wood; fungi production; water harvesting and conservation; aiding soil biology; soil rehabilitation and conservation; improving soil structure and composition; improving irrigation; tree and forest establishment; and growing annual and perennial plants for food.
One of the primary benefits of Hugelkultur beds is their ability to hold moisture, increase water retention, build fertility, and maximize surface volume to increase the available growing area. As the years pass, the deep soil of your raised garden bed will become incredibly rich and loaded with organic materials, nutrients, air pockets for the plants’ roots, moisture, life, and many complex mini-ecosystems. They can even retain water better than humus alone. Although, as the bed decomposes, the wood will turn into humus, and, over a long period of time, the bed won’t be able to hold water as well. Although, it makes up for this by being able to hold onto other useful nutrients and oxygen better than the wood.
The logs and branches under the ground act like a sponge, soaking up water in the winter and spring, and holding it throughout the season. When it rains, rainwater is passively absorbed and stored in the mound, and gets released back into the ground during the summer. The plants’ roots then lick at the moisture contained within the logs, irrigating them in dry times. This makes Hugelkultur great for growing many kinds of fruits, vegetables, or herbs, and it is suitable for almost any kind of small and large plants. The beds require no tilling, need little irrigation (even in dry climates), and last for years.
And, by holding so much water, Hugelkultur could be used to grow crops in the desert with little or no irrigation. This makes Hugelkultur incredibly useful in dry climates, and it can turn barren lands into a virtual oasis within just a few years. This is due to the mound’s incredible water-retention abilities. As raised beds tend to be a bit drier than traditional beds, a Hugel bed is a good solution for a raised bed in a dry climate. The drier your area, however, the more wood you will need to hold the necessary moisture.
The mound also holds and preserves nutrients for the plants, even after a rain. This sometimes may be a problem in traditional planting beds, because after a rain, any nutrients in the top soil are washed deeper into the ground. But, in a Hugelkultur bed, the water and nutrients are captured and contained by the rotting wood, being preserved for the long term. This means you may never need to water the bed after the first or second year, except during long term droughts. The greater the mass of the bed, the greater the water-retention benefits it will have, meaning the more wood there is inside, the less water it will need over time. The bed will store water and give nutrients for many years to come, and may need little or no supplemental water or fertilizers after establishment.
Hugelkultur has a vast array of uses as a solution to many problems that could plague gardeners. It can be used in areas where the soil is basically structure-less, like decomposed granite, which becomes a waterlogged slurry when wet, and sets like concrete when dry. This can be dealt with by using the beds as a swale, burying the logs on contour in the path of the bed so it can absorb the water when it rains, but also leave excess water to run away. This way, you could use them to passively create ponds using swales in gullies. You could also build them on terraces, and cover them abundantly with high, flourishing beds. Another option is to cover them with pallets around the periphery to make a wooden border or frame.
Clay can also be added to the mix, because clay stores lots of water through the dry summer and fall. Beds made with a clay mixture added to their soil will hold more water and add nutrients for more years, potentially feeding fruit trees. You can even use sandy soils, as in sandy properties plants seem to grow a lot faster. You can combine them with a chicken coup, as well. Just bury some rows of trees and grow more productive species using poultry manure as a nitrogen source. Use Hugelkultur to create extensive, sustainable food gardens with a property where the entire south side is available for planting. Fungus can also be cultured in your bed by seeding the wood with mushrooms.
Another use of Hugelkultur is for waste management, and to dispose of unwanted woody organic matter. Most people get rid of wood by simply collecting all their scrap brush into a pile, and burying it under some grass clippings and soil, or by burning it. Others try to solve the problem by taking it to the dump, merely shifting the problem to somewhere else, turning it into someone else’s burden, without actually resolving the issue of the unused waste. The side effect is that this waste eventually accumulates, and improper storage leads to its decomposition and the buildup of greenhouse gasses (adding to climate change). It also produces excess materials that could create a fire hazard. If you are harvesting the woody matter locally, installing a Hugelkultur bed can save you a lot of energy that would otherwise be wasted just by disposing it. Sourcing your wood locally is beneficial, since you can put your waste wood to a productive use, without spending energy chipping them, burning them, or taking them to the dump. This can help reduce the load of turning these materials into waste, while at the same time creating a fertile plot of productive land.
If you don’t have any of your own spare wood, or you don’t live in an area with any available brush (such as in an urban or suburban neighborhood), you can often look around for public facilities that produce waste wood. Most municipalities have green waste programs (such as tree clearance around power lines, or ones that keep the sides of the roads mowed) that can offer you a free local source of waste material. Also, look for local businesses such as arborists or landscapers to acquire larger logs. Furthermore, Hugelkultur promises to be a way to manage small woodlots and dry, forested areas. You can use this technique to cull trees, clearing woodlands without having to burn the excess lumber. The objective is to break up continuous forests in favor of clusters of trees to promote the health of larger, more fire resistant trees.
Other uses for this method includes sequestering carbon into the soil, helping to reverse climate change. This is preferable to burning excess wood, which exports carbon into the atmosphere. However, by using Hugelkultur beds we can store that carbon in the ground, saving the world from global warming in your own back yard.
Another advantage for Hugel beds is protection from seasonal flooding. Hugelkultur can help reduce the damage from floods, as most of the plants are elevated above ground level, meaning they will suffer fewer losses, as fewer plants will be drowned or experience root rot from the continuous moisture. This is true about raised beds in general, although, with conventional raised beds, the soil can eventually get more muddy compared to Hugel beds. You can also use Hugelkultur to manage the flow of water on your land. Simply use the terrain, ponds, and swales integrated with your beds to direct water to where it is needed.
How They Work
This gardening-style is inspired by the way forests naturally recycle their own resources. If you take a walk in the forest, you may observe that the ground feels soft and spongy, and almost seems to be alive. This is from all the years of fallen wood, leaves, and other natural organic materials, that accumulate on the forest floor and break down into mulch, re-fertilizing the land. And, inside of this layer of organic mulch, many kinds of microorganisms will take up shelter and create a living habitat.
Hugelkultur simulates this natural process, recreating the way nature manages itself, and recycling the wood in the same way as the natural environment. The wood acts the same as a rotting log laying on the forest floor, which attracts microbes and behaves as a sponge for moisture. If you take one of these logs and split it open, taking off the top decomposing layer, you will likely find a moist environment full of life right under the surface. It will also be, on average, more moist on the inside, because, when buried, Hugelkultur beds retain even more water than raised beds. This moisture will remain constant in all but the most scorching of droughts.
In addition, because the decomposition process in Hugelkultur takes place below ground, feeding and watering the soil, the woody matter in the beds will soak up and holds nutrients, helping to keep them from passing into the ground water. This way they can be stored and held for later, refeeding your plants. And, as the buried wood in the beds slowly breaks down, it will provide all the nutrients needed by the plants. This decomposition releases nutrients into the soil, and builds up a layer of humus, or accumulated plant and other biological material, for the future.
The gradual decay of wood creates a consistent source of long-term nutrients. A large bed might give out a constant supply for 20 years, depending on the volume of wood, its species, and longevity, or resistance to decay. This way, the bed will self-fertilize over time, and (although it may need additional compost and organic fertilizer early on), after a year or two it will basically become self-managing, while at the same time allowing you to cultivate both annual and perennial crops, including many edible, ornamental, and functional plants.
In addition to this capability for long-term self-fertilization, storing and preserving nutrients, a properly created Hugelkultur bed does not need to be tilled at all, since, as the wood breaks down inside the bed, it will start to collapse and shrink down in size. This shrinkage, however, is normal, and the mound may decrease so much that one built to an initial height of 2.1 m will drop to 1.8 m or less within the first few months to a year, and may continue to shrink until the second year.
As the wood breaks down further, the openings on the inside will expand and fill with air, creating air pockets that bacteria and mycelium can invade, further hastening the decomposition. These pockets will eventually collapse, shrinking the size of the bed over the first year or two. As it shrinks further, shifting the positions of the logs and soil inside, it creates tiny air pockets in the soil that aerate the bed. Soil aeration thus increases as the branches and logs in the bed break down, causing the mound to self-till.
This shrinkage can be counteracted by adding a fresh layer of chop and drop green manure or compost to the surface of the Hugelkultur bed each year. It can also be accounted for by starting out with a bed slightly larger than you intend it to be in the end, once it’s settled. To care for the bed after setting it up in the subsequent years, simply add compost on the top whenever you plant, and fill in any planting pockets with green materials, as needed. As the wood continues to decompose and shrink, the leaves, duff, and accumulating organic matter from above will take the place of the wood begin decomposing, and changing it all into humus.
Another necessary factor in Hugelkultur is the micro-organisms that live in the bed, serving as a key component in the composting process, since it’s their work that decomposes all the woody matter in the bed. The energy created in decomposition also generates heat, and becomes the fuel for the life in the soil, like mushrooms, worms, termites, beetles, etc.
Methane And Carbon Dioxide Production In The Process of Decomposition
One may argue that composting is not that superior to burning, or accumulating the wood in exposed heaps or rubbish piles (i.e. garbage dumps), because burying produces carbon dioxide and methane, both of which are potent greenhouse gasses, and thus it is also a form of pollution. This is an important issue, as if Hugelkultur beds do produce greenhouse gasses, it would be critical to know this before scaling up the method to bigger use.
However, because the decomposition of wood in a Hugelkultur bed is very slow, this isn’t too much of an issue. One must realize that this methane and carbon dioxide production is not a one-way process. In fact, there are additional processes within the bed that reduce the amount of gasses released by the bed.
To realize why this is so, one must understand that all things biological decompose over time, becoming food for the soil. During this process of decomposition, the process is catalyzed by microorganisms in a complex process using these specific formulas:
CxHy+(x+y/4)O2=xCO2+(y/2)H2O And 2C organic+2H2O=CO2+CH4
In the first formula, during the decomposition that takes place during decay, oxygen is combusted and combined with hydrocarbons. And, at the completion of the process, the final product is heat and, primarily, carbon dioxide and water. This is also true for all living organisms, including humans. A proportion of this carbon, however, will be diverted for a time into the bodies of bacteria, fungi, plants and animals, temporarily diverting it back into the biological circle of life, being recycled back into nature. But, eventually, we all end up being converted into carbon dioxide and water, with a relatively small amount of iron, calcium, phosphorus, and other remaining elements.
If you bury this material underground, it will still decompose and release gasses, but it will take longer to release into the atmosphere. Most of these materials will be reabsorbed back into the environment and stored safely underground via carbon sequestration. If some of the buried carbon doesn’t decay quickly, it could become a carbon sink and absorb it so that it does not get released into the air. There is also evidence that this carbon can stay in the soil for considerable amounts of time, lasting for many years. But there are other pathways for the carbon to go depending on the flora and microorganisms that it encounters. It could, for example, be transformed into energy via photosynthesis by plants, which, chemically, is the opposite of the process that happens during decay. In decay, biological matter is transformed to separate and release carbon dioxide, splitting them into separate molecules. During photosynthesis, however, sunlight energy is used to do the opposite of decomposition, combining carbon dioxide and water together to produce new molecules in the form of carbohydrates. In this way, the carbon dioxide levels are managed via the cultivation of new plants, which breathe the gasses, reducing their concentrations in the atmosphere.
The carbon could also be taken up by the bacteria and other ground biology in the soil, which will reach up to grab it and transport it and other nutrients underground. This makes the energy in all the biomass buried in the bed available to all the other little creatures and life in the bed—fungi, mycorrhizae, bacterium, insects and more—giving them the food they crave and an ideal environment to thrive in. The carbon dioxide produced by the composting process can also be offset by the fact that we are using this compost to grow more plants, which breathe the carbon dioxide, producing oxygen, and helping to reduce carbon levels in the atmosphere. The result is that carbon pollution is minimized as a result of composting when used in the context of gardening.
In the second formula, during decay two organic carbon molecules are combined with two water molecules to produce carbon dioxide and methane. Both methods and processes are largely achieved by micro-organisms, which are ultimately responsible for breaking down those biological materials inside the bed and transforming and releasing them into usable energy. A pile of wood has a lot of energy in it, which, when released, escapes in the form of heat. When burning the wood, the release of energy is equal to that which takes place during decomposition, but consolidated into a shorter period of time. Imagine burning this wood in a bonfire. When burned, the woody matter is ignited and consumed by the flames, gets converted into energy, and is released as heat. Usually, burning only takes a matter of moments, and the entirety of the wood can be consumed in less than a day. By contrast, whereas burning takes anywhere from seconds, to minutes, to hours, decomposition takes weeks, months, or years.
In addition to the energy releasing in the form of heat, it also instantly produces greenhouse gasses. Burning produces various pollutants, causing an immediate production of carbon dioxide. The decomposition in composting, however, is slow and produces little to no excess pollutants or greenhouse gasses. It is for this reason that burying is usually preferred to burning, as burying builds up and rejuvenates the soil, putting back the nutrients and minerals taken up by the trees, while burning depletes the soil by taking carbon out and releasing it into the atmosphere, adding it to the global store of pollutants. In other words, burning just bypasses all of the processes of decomposition, and goes straight to producing heat and greenhouse gasses, without capturing the carbon in the soil or in the bodies of heterotrophs that eat it.
Usually, inside the micro-environments in these heaps, when left alone, they will tend to create micro-environments that are anoxic, meaning totally depleted of oxygen. If anoxic conditions occur, then methanogenic bacteria (or bacteria that produce methane in anoxic conditions) will take up the area as a living space, and use organic molecules to produce methane. Anoxic environments are more common than you expect, and methanogenic bacteria are ubiquitous, meaning they are everywhere. Additionally, because a Hugelkultur bed is predominately filled with rotting wood, there will tend to be more saprophytic fungus—fungus that feeds on dead things—than bacteria, which prefers an environment more akin to the humus we will eventually create. This may cause some Hugelkultur beds to become anaerobic, and will produce an excess amount of methane when the trees decompose.
This would lead one to conclude that a considerable amount of methane will be produced over the lifetime of the mound. So, given these facts, we must ask, why are we not overwhelmed by methane? And, in addition, why is there so little of it in the atmosphere? The answer to these questions relies on a number of factors, although the solution for this relies in the complex microbiology in composting and the buried vegetation of Hugelkultur.
The first one is that the bacteria that thrive in anoxic conditions are strictly obligate anaerobes. These microbes cannot tolerate high levels of oxygen, and are poisoned by its presence at levels as low as 0.18 mg/L of molecular oxygen. Composting, however, when done well, constitutes a partially aerobic environment where methanogenic bacteria will not be able to thrive. So, if you aerate your compost heap well enough, these bacteria won’t produce as much methane.
The other reason is that there is another set of bacteria called methanotrophs, or methanophiles, that also may take up the heap as a habitat, and are able to use methane as a source of both carbon and energy. What is more, they can also grow aerobically (like Methylococcus capsulatus), or anaerobically. This means that, regardless of where the methane is formed (in the compost heap or deep in the ground), these bacteria can metabolize methane by either incorporating the carbon into their bodies, or by producing carbon dioxide and water in energy production. Some, like Methylomirabilis oxyfera, with the help of other microbes, actually reduce nitrate to nitrogen and contribute to nitrogen loss in the soil.
The difference between the relatively aerobic conditions of a compost heap, and the relatively anoxic conditions of buried vegetation, is the speed at which methane can be metabolized. Anaerobic decomposition is a relatively slow process. In addition, some Archaeons (single-celled prokaryotic microorganisms) may be implicated in the breakdown of methane by sulphate reducing bacteria, which leads to the characteristic smell of hydrogen sulphide (or rotten eggs), that is sometimes associated with the breakdown of organic matter. This would reduce the methane content produced by the bed, but would also produce a bad smell, which is undesirable.
As methane use by methanotrophs is slower in anoxic environments, if you do not aerate the bed, then methane production would increase and overwhelm the methanotrophs, resulting in a buildup of methane. But if you bury comparatively small amounts of green matter, which the soil methanotrophs can deal with fairly easily, this will allow them to thrive and grow. So, composting and burying vegetation, if done correctly, will produce no more methane or carbon dioxide than burning, and may in fact produce less.
Choosing and Gathering Wood
Some things should be considered about certain kinds of woods. The first and simplest to answer is the size of the wood. How big can the logs be? Your logs can be massive, although you may have to chop them up into smaller, more manageable chunks to move them. Use up to 15 big logs, 2’ x 3’ long each, buried along with a ton of branch debris for each bed. Try to stretch out these logs enough to fill the bed to capacity, and use this as a standard unit, or measuring stick, to determine your resource needs when building the bed. This will allow you to scale up the bed significantly when needed.
There is almost no limit to the size of the logs. The only problem is covering the logs with top soil. If you think the logs you have are too large to fit, you can simply dig out a trench about 2 ft. down, put the logs at the bottom, and then cover with top soil to bury them. If you don’t have any heavy machinery to help do the lifting, you will have to cut them down to size first so you are able to pick them up and move them.
Most woods will work in Hugelkultur, but some types are better than others based on how you use them and what you want to grow. The most obvious fact is the rotting wood acts as a carbon source, and breaks down over time. As the fresh wood rots, it will absorb nitrogen and start to break down faster and faster, giving this nitrogen back to the soil. If you use wood chips, or many smaller twigs and branches, the wood will have a greater surface area and thus break down quicker, and release nitrogen faster.
Try to accumulate pieces of wood over time, store them, and allow them to rot a few years before use. Rotten wood is the best wood to use in Hugelkultur. The wood can be in the form of branches, whole logs, old firewood, or even chips, but Hugelkultur beds work much better if the wood is not chipped. If you don’t have a strong supply of wood of your own, ask your local power company to drop a load for you, as they usually collect lots of it from doing work on street side power lies.
Try to avoid fresh wood, if possible. By using carbon-rich fresh wood, you may decrease the overall nitrogen content of the pile in the short term, because the wood will initially rob the surrounding matter of nitrogen. This is because, during the first year of breakdown, the wood and fungi will steal a lot of the nitrogen out of the surrounding environment. This means the bed will be low in nitrogen at first, as newly decomposing wood eats up a lot of it. But, after a year or two, when the wood has absorbed nitrogen to its maximum capacity, the wood will start to break down and give the nitrogen back to the soil.
This can be counteracted by using rotting logs that have absorbed much or all of their total nitrogen holding capacity. Or, it can be compensated for by periodically adding urine to the heap, as urine contains ammonia which breaks down into nitrogen. Simply keep a dedicated bucket for yourself that you can fill and re-use. Also, add plenty of strong sources of nitrogen-rich material (such as fresh grass clippings, green or dead leaves, seaweed, straw, leaf mold, manure, etc.) right on top of the wood as it is being built to help jump start the composting process. Another method is to plant nitrogen-feeders, or crops that add nitrogen to the soil (like legumes), or to plant species with minimal nitrogen requirements. In the end you will be left with a beautiful bed of nutrient rich soil.
The best woods to use are the softer kinds, as opposed to the harder, denser woods. This is because hard woods break down slowly, taking longer to rot, and release their nutrients much more gradually, usually resulting in stunted growth early on. This is useful if you want a longer lasting bed, and you don’t mind waiting around for the wood inside to decompose before you plant. Softwoods, in contrast, disintegrate faster, and release their nutrients quickly, making them useful for rapid, albeit short-lived growth. For a nice balance between the two, try combining wood types by putting softwoods and branches on top, with large logs and hard woods on the bottom. This way, the woods on the top will decompose first, leaving the other ones below, which will remain for much longer.
If you have enough space on your property for a wood lot, plant fast growing trees to be used in future. Poplars are useful because goats can eat the leaves, smaller branches, and even the bark. In addition, you can use them to make new garden beds from the thicker branches and wood. Black Walnut inhibits germination and lasts for a long time, making it excellent long term. It can also be used to rebuild grasslands. Simply bury a Black Walnut stump or log and plant a non food tree on top.
Some conifers release leaf litter and chipped bark with a higher pH than broadleaf trees, and if there is a considerable amount of chippings then it may change the pH of the soil. If this is the case, then the conifer soil pH will be consistently more acidic. Try to capitalize on this by growing plants that thrive in acidic soils, like Blueberries. Plant nice chunks of pine or Azalias under where you’d like to have blueberry and tomato beds. If the conifers are making the mound too acidic, or if you don’t want to grow acid-loving plants, add some sulphur to the bed as you build it. Adding calcium with eggshells would be even better, as these absorb acid and turn it into calcium salts. If you want to make the bed more acidic, add sulphur crystals to form sulphuric acid.
Other kinds of trees may be suitable for hugelkultur such as pear, plum, beech, linden, cornel, elm, chestnut, ash, hazel, elder, etc. These may have to be experimented with to determine their viability in different climates. Be careful if using cedar when planting, as new plant growth does not like freshly cut cedar. If you have some very old lumber or railway sleepers laying around that were not stained, painted, or treated with any harmful chemicals or preservatives, then you could probably use those in the bed, too. Although, you will probably have to break these up, or turn them into chips. You could also use pine and bush chips, as long as they have already been rotting for a few years (preferably 3-5).
Sometimes, in heavily wooded areas, you may get some invasive poison ivy coming into your garden. These, however, could possibly be chopped up and used in your beds. Microorganisms have an extraordinary ability to decompose a vast array of chemicals. This means that some harmful chemicals, like the oxalic acid in rhubarb leaves and the irritant in poison ivy, would probably rot down to carbon dioxide, water and a few minerals in a Hugelkultur system, just like any other organic materials, rendering their toxic qualities nullified.
Woods that work best:
- Willow (dry or dead)
Woods that work okay:
- Black cherry (use only rotted)
- Camphor wood (well aged)
- Conifers (contain tannins)
- Eucalyptus (slightly anti-microbial)
- Juniper/yew (anti-microbial/anti-fungal, use only at the very bottom or unless already well aged)
- Osage orange (resistant to decay)
- Pacific Madrone
- Pacific yew (resistant to decay)
- Palm trees
- Pine/fir/spruce (these contain tannins and sap, which repel plant growth; use ones that have been dead for a few years so that the tannins have broken down)
- Red mulberry (resistant to decay)
- Leyland cypress (particularly resinous and may be allelopathic; use only chippings)
Woods to avoid or use with caution:
- Black cherry (toxic to animals, although the toxins may be gone after rotting)
- Black locust (greatly resistant to decomposition because it’s so dense)
- Black walnut (contains juglone, which is toxic to most plants)
- Bradford pear (invasive; will send sprouts growing up through the bed)
- Old growth redwood (heartwood will not decompose and redwood compost can prevent seed germination)
- Thuja (resists decay; use only at the very bottom)
- Cedar/walnut/juniper/yew or any allelopathic species (contains natural pesticides and herbicides, and has anti-fungal/anti-microbial properties; use only broken down bits at the very bottom, or if it’s already well aged)
- Calystegia sepium, Equisetum arvensis, Armoracia rusticana, Persicaria wallichii (all of these are invasive plants)
Another thing to keep in mind is that the wood will likely absorb nitrogen from the soil during the first year, taking it away from the plants. Woods that are high in carbon and will consume nitrogen as it rots down. Newly decomposing soft woods will also tend to absorb more nitrogen at first, taking it away from your plants. To compensate for this, there are a few simple techniques.
The first is to use older, more rotten woods, as these have already absorbed much or all of their total nitrogen holding capacity, and thus won’t take as much nitrogen from the soil. In general, aged wood is better than fresh wood, but rotten wood is better than aged wood. The more rotten it is, the better, as this will absorb less nitrogen, and may actually even release some of it back into the soil. For less desirable wood, make sure to let it rot more extensively before burying.
Secondly, use woods that have been cut the same day for best results, as this allows you to seed the wood with fungus, like mushrooms. In addition, be sure to add strong sources of nitrogen into the mound, and keep it topped off with additions of nitrogen-rich fertilizers and composts, and see if there is a fungus that thrives on your “problem” wood.
Thirdly, one opportunity you have when first building your hugelkultur bed is to choose to inoculate the wood with a desired species of fungus. This acts as a temporary barrier to other fungi and becomes food later in the process, after the inoculation has taken hold. The higher initial ratio of fungus to bacteria will promote tree growth, since the fungus interacts with the roots of the trees, trading nutrients for starches. The mycelium also aid in the distribution of the water stored in the rotting wood to the surrounding areas. To ensure successful inoculation, cover the ground with a few layers of cardboard, newspaper, or another kind of mulch layer, before building the bed.
Fourthly, grow nitrogen-fixing plants in the first year to replace the nitrogen lost to the new logs. You can also utilize plants that prefer to grow in low-nitrogen conditions. Then, in the second year, use plants that are nitrogen-loving and thrive in nitrogen-rich soils, or ones that don’t fix nitrogen, in addition to ones that do.
In the first year, grow:
- American Liquorice
- Autumn Olive
- Bog Myrtle/Sweet Gale
- Dyer’s Greenweed
- Goat’s Rue
- Ground Nut/Apios Hog
- Peanut Lentils
- Milk Thistles
- Northern Bayberry
- Russian Silverberry/Oleaster
- Salsify Sea
- Velvet Bean
In the first year, do not grow:
- Brussels Sprouts
After the first year, when nitrogen levels have been replenished, you can grow just about any kind of plants, including the ones in both lists, above.
How to Build Them
Creating a Hugelkultur garden bed is a relatively simple process. Start by prepping your new Hugelkultur beds in the fall before the spring planting. One strategy is to make them in the winter, and let them settle for the whole season so they can get colonized by microbes and start the composting process early in the season.
When ready to start building, first select an area approximately 6 ft. by 3 ft. wide or larger if you want to make a bigger bed. Site the bed-to-be in the sun if you’re growing vegetables, but a shade garden could be grown Hugelkultur-style, too by bending the shape of the bed into a horseshoe, hook, wave, spiral, zig-zag, or another curved figure. Next, you have two different options. You can either choose to mow the grass down on the area to be gardened, but do not till it up. Next, lay down lots of cardboard directly over the ground where you want to build to create an anti-weed barrier. Then, begin piling on your wood.
Or, for the second option, you can choose to start by building a pit where the beds will sit, by digging up the sod to make a 1-2 ft. deep trench. For those times that the soil is deep and you are moving the soil by hand, dig down by a foot or two. Even better is to figure out where the paths will be, and dig down there too. Then, pile in the wood, filling the trench with dead trees, fresh logs, brush from your hedge bushes, or even some old straw or hay. You could also add about 6 in. of composted brush chippings to the trenches.
Then, throw on a mix of dry and rotted logs of various types, dry branches, and lots of green bios mass, with woody bushes mixed with green manure and various mushroom, fungi extracts. Use whatever organic material you can get ahold of, and cover it with layers of branches, twigs, woodchips, and fallen leaves, or just about any kind of scrap plant material available.
Put the bigger wood in the very bottom of the hole, then add smaller limbs and pieces of wood as you build your way upward. Place the wood like a puzzle, allowing as few gaps as possible. The different lengths and widths of plant material create the structure for the beds. Stack the branches to about 1 ft. high, and cover them with a 4-6 in. layer of manure mixed with hay.
You could put sticks in the bottom, building up a loose layer in place of the large logs, but the sides won’t be able to grow well consistently due to erosion. Because of this, it’s simpler to bury the stump in the soil, adding at least 6 in. of soil on top, and plant on that. However, it’s best to chop up the stump a bit first, to give it a greater surface area to absorb water.
Next, rake your leaves into garbage bags, toss in some dirt and some water. Use this later to fill the spaces between your Hugelkulture logs (it will be reduced to near powder by the dirt organisms), as the most excellent inoculant. Add grass clippings and other finer nitrogen-rich organic matter to fill the gaps left between the logs. Add a little bit of urine here and there to provide some nitrogen to stimulate the sticks breaking down and the plants growing.
It would also be advisable to build up around the sides of the stump with bales of hay, sticks, leaves, etc. Next, add 6 in. of turf, with the grass-side down, completely covering the logs. Instead of soil, you could also use a mix of compost, manure, and leaves.
On top of the turf, add nitrogen rich and compostable material like grass clippings, seaweed, compost, aged manure, straw, green leaves, kitchen waste, and mulch, cardboard, petroleum-free newspaper, or any other biomass. Stack these all in lasagna-like layers on top of each other to create a rich, compostable layer that’s great for areas with poor quality soil.
Top off the bed with 1-2 in. of top soil and a layer of mulch. Then, cover it all up with compost, old hay, soil and very aged horse, rabbit, or milking cow manure. You can also add to this some clay soil mixed with sharp sand from the river and cow manure, be it green or otherwise as this will improve drainage of the bed, with the sand, or increase the soil’s water retention with the clay.
Lastly, cover the whole heap with 5 cm of top soil. Lastly, cover the whole heap with 5 cm of top soil, and plant on and around it. Mulch with straw, hay, or glossless newspaper to keep away unwanted plants, and water each of these layers liberally as you build them. Keep adding compost material for the first year or two to regenerate the nutrients in the beds. Do not use any store bought fertilizer. If you use grass clippings, make sure the ones you use do not come from any chemically treated turf, even if it did not contain the persistent herbicides that cause “killer compost.”
Sizing the Bed
The size limits of hugelkultur beds are up to you. Beds with a height and/or width of up to nearly 2 m are not uncommon. You can make smaller mounds of about 60 cm in size, made of rotting wood placed right on the ground, and covered with a small layer of dirt. These smaller micro-Hugelkultur beds can be easily built if you only have some smaller woody material to dispose of.
You can also do a Hugelkultur bed right on top of the sod. Just put the logs on the top soil and cover them with soil obtained from elsewhere. If excess soil is not available, then simply place some sheet mulch over the logs and branches, and layer them on top of each other like a lasagna to better facilitate the process of composting. One could also use Hugelkultur to get rid of old, dead stumps. Simply bury the stump at ground level, and proceed with the bed as normally. The old stump will bring up water and decompose, adding nutients to the soil.
If you’re making a conventional raised bed, put the wood in there first, before filling it with soil and compost. Use woody debris as a base layer inside your boxes.
Cover your woody base with compost, a little soil, straw, old manure, spoiled hay, grass clippings–whatever organic material you have, to a depth of about 12 in. on top of the wood. If you have Nitrogen-rich material such as fresh grass clippings, put them right near the wood to help it get started breaking down. Within a few days the bed will start to settle down
Build your beds up to 6 ft. tall. The higher they are, the more water they will retain, and the less you need to irrigate them. If you are going to build beds shorter than 3 ft. tall, you should make the beds no wider than 4 ft. The slopes should be at least 45 degrees, depending on how high or wide you want them. Although, you can increase them up to 60-70 degrees if you need to increase the growing space in a constricted area. Many raised beds fail because their slopes are less than 45 degrees. This leads to compacting of the soil, so new plants cannot establish themselves. It also restricts the amount of oxygen that gets to the decomposing material, resulting in anaerobic rotting. Use the table above to determine the correct size and slope for your bed.
|Desired height||Desired slope||Width of trench to dig|
|1 m||45°||2 m|
|1 m||60°||1.2 m|
|1.5 m||45°||3 m|
|1.5 m||60°||1.7 m|
Areas with a deep root-zone, or a rhizosphere, can be anaerobic, depending upon local conditions, mostly due to water saturation excluding air. Perennial alfalfa, for example, has a very deep root system, and could create an anaerobic environment, suffocating most of the beneficial microbes, and inviting harmful ones. To guard against these conditions, build your beds to be 4-5 ft. across and 4 ft. high. Beds built at these measurements will tend to be more aerobic throughout because of good drainage and less soil compaction, making more air available for aerobic microbes.
To get the most benefits out of a hugelkultur bed, build it to an initial height of 2.1 m. As the wood decomposes, it makes tiny air pockets that micro-organisms like bacteria and mycelium can invade. These air pockets eventually grow and collapse from the weight of the bed, causing it to shrink over time. As a result, the bed will shrink to 1.8 m or less (generally by about 1/3 of the original size), within the first few months to a year. Counteract this by adding a fresh layer of chop and drop plants, green manure, or rich compost to the surface of the Hugelkultur bed each year.
A 60 cm tall, above-ground hugelkultur bed can maintain a usable level of moisture for about 3 weeks. Larger beds of 1.8 m or higher can hold enough water for an entire growing season. If you build your hugelkultur raised garden beds tall enough, after the second year, you won’t have to irrigate them at all. To go all summer long without a drop of rain, build your hugelkultur raised bed gardens up to 6 ft. tall. But they’ll shrink, mostly in the first month, which is why you should actually build them 7 ft. tall at the onset.
Build your Hugelkultur raised garden beds about 5 ft. wide. This makes for some mighty steep beds. Just pack that soil on tight and plant it with a mix of heavy rooted plants to hold it all together. Use steep hugel beds to avoid compaction from increased pressure over time. Steep beds mean more surface area in your garden for plants, and the added height makes for easy harvesting. And with a really tall, steep raised garden bed, nobody will ever step on it, so the soil will not become compacted.
If the soil does become compacted, improve it by trenching between the rows of trees and burying prunings and manure. Also, try to plant white clover on the slightly raised surface, which can make good company for walnut trees. This will add to your soil’s water holding capacity, as well as improve drainage to help diminish the effects of Phytophthera fungus, which seems to thrive in compacted soils.
Hugelkultur raised garden beds can be built just 2 ft. tall and will hold moisture for about 3 weeks. Some people will start out with Hugelkultur beds that are 2 ½ ft. tall and plant only annuals. And each year they will build the size of the bed by a foot or so. After a few years, the beds will have gotten much bigger, but the neighbors never really notice, since it grew only gradually.
To decrease the height of your bed, but still use a lot of materials, you can partially bury the bed. This should not be a problem in design or application, as the beds can be partially sunken or raised, being installed completely below ground, or even with the top layer a bit sunk in.
It can be flush with the ground, although raised garden beds are typically better. You can start small, and add more to it later, although bigger is usually better. Simply dig a ditch, fill it with logs and nitrogen-rich organic matter, and bury the lot of it under a layer of top soil. Partially burying the bed can be useful in very arid environments to better conserve water and reduce evaporation. The deeper you bury your woody material the better, since as the roots grow down deeper into the rotting core of the bed, they are going to be treated to a more stable, nutrient rich, self-replenishing water source. In addition, with a bigger size, more heat will be generated, and it will last longer due to the high carbon content of the wood in the middle, and due to the high insulation of the surrounding soil.
Some people don’t like raised beds because they consider them unsightly, and prefer beds that are set lower down, or even flush with the ground. Some people are okay with raised beds that are 3-6 in. tall, but no higher than that. If you are going to build beds shorter than 3 ft. tall, then make the beds no wider than 4 ft. Although, if you are doing keyhole style raised garden beds, then you could be able to get away with something wider. Some people dig a trench 5 ft. deep, fill it with organic matter, and have something that is either flush with the surface, or one that appears to be only 1 ft. tall (which is in the comfort zone of neighbors). Other people will build something that is 18 in. high the first year, and add 1 ft. each year. However, beds that are down low to the ground like this do not benefit much from one of the best aspects of raised beds — the increase in surface area available to plant from the mound.
You could also use square hay bales to create a Haygelkultur mound, or surround the mound with hay or straw bales to create a border. This adds even more benefits, as straw bale gardens require less soil, less water, and also hold more heat. This straw border surrounds a woody interior, combining the positive aspects of hay and straw with Hugelkultur together into one system. And as the straw breaks down, it adds more nutrients to feed the plants, creating a nutrient rich border for your bed. The downside is that the hay doesn’t last as long as wood, having a lifetime of about 5 years instead of 10-20 years. However, hay and straw will still give you a bed that supplies moisture and nutrients for a significant amount of time.
To create a Hugel bed with buried hay instead of logs (also known as Haygelkultur), simply stack your hay bales in a 2-step pyramid, and cover them with compost and soil to smooth out the voids, making a solid, parabola shaped hill that runs down a line. Then, cover the mound with leaves and grass for additional compost, and lastly, cover that with overturned top-soil.
Other modifications can be made to improve the aesthetics and functionality of the bed, as well as to make climate based modifications to make it more applicable to specific areas. Make any shape that you want, perhaps a keyhole-shaped bed, or put several of those together, and you can have a mandala-shaped garden with paths that create an easily walkable path on the inside. The beds with the keyholes could be about 6 ft. wide. One option is to make the bed longer (30, 50, 75, or even 100 ft. long), and fill it full of pathways all throughout. Make the final bed size be about 4 ft. wide in the trench, with a finished size of 6 ft. at the base, separated by 2 ft. wide access paths. Adding a zig-zag shape to the bed will increase the planting surface area even more. If you have lots of big logs made of woods that resist decomposition, then try putting these along the border of the beds to create a strong, heavy, long-lasting retaining wall.
Other building options for Hugelkultur include: standard beds, narrow beds, peaked beds, beds with a stone or log border, terraced beds, Hugel spiral, Hugel hoop, beds shaped into a sun scoop (angled towards the winter sun) to protect sensitive plants against frost. Swales are excellent at creating frost pockets which works to your advantage in the summer. Construct a terrace to hold the Hugelkultur bed. Combine several beds together (both small scale and large scale), to increase the size of the beds indefinitely.
You can put down borders around the beds, using different materials to define the edges of the beds, to give them a solid wall to contain them, or to make a walkable pathway, using things such as stones, logs, pallets, or even 2-by-8 in. boards. Place rocks around the border of the bed and rework it a little into a slightly more elegantly designed raised bed. The stones will also retain more heat, helping to extend the growing season further. It also adds a stronger structure to its perimeter, creating a load-bearing wall that permits you to build up the bed even higher.
Hugelkultur beds can even be built in an urban lot, like in between the curb and the sidewalk (sometimes called a parking strip), or even on top of a concrete slab. This has some advantages, as it gets the best sun, and you can still build plenty of soil on top to allow the plants to grow, although their growth may be restricted. Only do this if it’s the only spot available, or if you just really want to cover up a concrete eyesore.
- Autumn Olive
- Bog Myrtle
- Brussels Sprouts
- Butternut Squash
- Fig trees
- Fruit trees
- Ground Nut
- Hog Peanut
- Sweet Potatoes
- Velvet Bean
Just about anything will grow in a hugel bed, including most annuals and perennials (which are great for Zone 1 hugel beds), although some plants will thrive even more so than in regular beds. Onions, for instance, are much more vigorous in Hugel beds, compared to those grown conventionally. Some plants do especially well, such as herbs, eggplants, peppers, potatoes (regular and sweet), plants in the cucurbit family (cucumbers, squash, gourds, watermelon, zucchini etc.), strawberries, raspberries, and blackberries. Most perennial fruit will thrive in Hugel beds, as woody perennials can take advantage of and benefit from all the wood and fungal relationships inside the beds. Areas that receive high to moderate rainfall, which have extra moisture retention, may even find new, riparian species growing where you would not otherwise find them. The only drawback is it is harder to get germination on the sloped sides, and it tends to get a bit dry at the very top, which could call for extra irrigation, if needed.
Fruit bushes also grow very effectively on the crest of the bed. If you wish to use the raised bed as a windbreak, build the bed with its length running at right angles to the direction of the wind. In addition, make the sides steeper (about 60-70 degrees), and plant the top of the bed with tall plants such as sunflowers, hemp, or Jerusalem artichokes. Also, try planning your beds to form a swale on a keyline or tiles to move water from a seasonal spring down the ridges of a valley covered in blackberry patches. Expect to have far more flavor in any tomatoes and berries you grow on these beds as well.
Be careful what you plant on newly made beds, as sometimes, because of the fresh wood, the crops won’t be able to tolerate the low-nitrogen content. Some plants actually do well despite of this. New beds do well with potatoes, for instance, which don’t crave lots of nitrogen. But don’t try to plant corn on a new Hugelkultur bed, as corn is a very heavy nitrogen feeder, and will drain it from the bed, depriving it from other plants.
It’s best to prepare the bed several months before planting and not to build them until just before the planting season, as they should be planted immediately after you build them, while the soil is still loose. If you’re in a temperate, northern climate, for instance, start building the bed in the fall to be ready for planting in the spring.
Utilize efficient time stacking to plan out when exactly are the best times to plant, based on your season, climate, and location. Start by planting crops that love all that dense, rough, woody material like squash, melons, or other vining plants first. Plant seeds or transplants into the Hugelkulter bed as you would any other garden. Whenever you plant, add some extra wood and compost to the surface. Also grow peas and beans for the first year to help get it going. But, be careful not to include any willow, currant or forsythia.
After the first 3-5 years, the soil will change dramatically in its composition and characteristics, presenting new opportunities for gardening. At this time, the inside of the bed will have transformed into mostly humus and deep, rich soil. You may also notice that trees planted on or around the Hugelkultur bed will see improvements with the extra fungal life in the soil. As well as storing a large amount of coarse organic matter, a Hugelkultur bed can gradually improve the soil by planting deep-rooted trees, grasses, and herbs that channel and capture nutrient-rich water from upland forests. Planting trees beside coarse organic matter, such as in Hugelkultur, will improve their growth. As the trees reach maturity, the fungus of the rotting wood will subside to reveal a more vibrant bacterial life more suited for smaller plants. This is an important part of creating sustainable agriculture.
Some pests have a tendency to invade Hugelkultur beds and interrupt the system. Termite colonies could become a problem as they will be attracted to the wood buried in the mound, and could redirect their hunger toward other sources of wood on your property, including your house. Voles, wood rats, or squirrels could invade the beds and consume your plantings, requiring you to dig it all up and start over. Crawdads could also get into your beds by burrowing, but these are usually more of a result of flooding than the method itself.
To stop rodents and insects, you could rely on snakes or other predators, like lizards, dogs, cats, and birds (chickens, ducks, turkeys, hawks, etc.) to help clear out these pests, but they may not be enough. It is best to enclose the garden in a fine mesh net to prevent infestations. This way, you can better control what animals get inside, and let in only demolitors (pillbugs, worms, etc.), and the above mentioned predators, if necessary. If insects and other arthropods and small, creepy-crawly critters (like termites) turn up in abundance to the point of being overwhelming, try running some chickens over your beds to clear them out, and turn a nuisance into an asset.