Hugelkultur Gardening Method & Hugelkultur Raised Beds

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Robert Pavlis

You have probably heard the name; hugelkultur gardening (pronounced Hoo-gul-culture), but few people have actually tried it. It is also now being used to make hugelkultur raised beds.

Is this a gardening technique that you should try? What does the science say about it? Should we all stop what we are doing and make hugels?

Hugelkultur Gardening Method & Hugelkultur Raised Beds
Hugelkultur Gardening Method & Hugelkultur Raised Beds, Photo source: RichSoil

What is Hugelkultur?

Hugelkultur is a gardening technique that has been used for many years in Germany and has been recently popularized by permaculturalist Sepp Holzer. It is a process for creating a new garden. Pile up some logs and smaller branches, cover it with leaves, sod, compost, grass clippings, seaweed, aged manure, straw, green leaves, and soil. The result is a new kind of raised bed without walls, that looks like a small hill.

There are many variations on the theme. A hugelkultur garden can also be made by first digging a trench and placing everything in the trench. This will still produce a raised bed, but it will be shorter than the traditional six foot tall design.

Growing Great Tomaotes, by Robert Pavlis

Raised bed enthusiasts have claimed the idea and modified it to suit their purpose. After building walls for a raised bed, they fill the bottom with logs and twigs, before adding the usual raised bed mix. This design is called a hugelkultur raised bed.

Over time, the pile shrinks as the organic matter slowly decomposes. Every five years or so it is rebuilt.

Hugelkultur for Raised Beds

The modern interest in raised beds has resulted in a variation of hugelkultur being used in them whereby users fill the base on the bed with wood. For a more detailed description of how to fill a raised bed see How to Fill Raised Garden Beds Properly.

Claimed Benefits of a Hugelkultur Garden

The wood in the system provides the main benefit which is the retention of moisture. The wood absorbs water, holds it for a long time, and slowly releases it to plants, thereby reducing the need for irrigation.

Other claimed benefits include the following

  • No need to dispose of waste wood
  • No CO2 produced by burning the wood
  • Increased surface area for gardening
  • Composting wood generates heat extending the growing season
  • Can help end world hunger

Lets look at each of these.

No need to dispose of waste wood

This is partially true and proponents of hugelkultur make a big deal about this benefit. But the wood could be chipped up and used as mulch, or it can be piled up, providing a habitat for wildlife. I don’t think most gardeners worry about getting rid of waste wood.

No CO2 produced by burning the wood

Burning the wood would release CO2, but decomposing it also releases CO2. Burning does produce other toxic chemicals which makes it a poor choice for disposing of wood, but I am not convinced the CO2 angle is a valid argument.

Maximize surface area

This is a valid point. If you are growing up the sides of the hill there is more surface area to grow on. But there is only so much soil, so can you actually grow more plants? This probably depends on the height and width of the hill.

Microbe Science for Gardeners Book, by Robert Pavlis

At least one side of the hill get less sun, no matter what orientation you use. This can be a problem for people in far northern and southern latitudes where they need all the light they can get.

Composting wood generates heat extends the growing season

Wood composts very slowly so it will produce very little heat. A newly made hugelkultur hill contains a lot of organic matter and this will generate some heat as it decomposes, but the decomposing wood produces almost no heat. As with any compost pile, the heat is generated when the pile is new. Once most of the easily composted material is partially composted, heat production slows dramatically.

Since many recommend not using the pile right away, the benefit of extending the growing season due to heat, is not a valid point.

A hill of soil does hold less snow and captures more sun in spring. It also drains sooner. For these reasons you should be able to plant earlier on the south side of the hill. The north side will stay colder than flat ground, making that side a late planting, but this has nothing to do with decomposing wood.

Can help end world hunger

What nonsense!

What Does Science Say?

Almost nothing. This is not a technique that has been studied by mainstream science. Most government offices don’t really consider it a valid gardening technique.

A couple of PhD thesis have been published. One suggests that hugelkulture does not rob plants of nitrogen (discussed below) and another one found hugel gardens held more water than non-hugel plots, but the data set was very small.

Anecdotal Information From Gardeners

Planted hugelkultur bed, photo source: hellohomestead
Planted hugelkultur bed, photo source: hello homestead

The internet is full of information that shows you how to build a hugelcultur garden, but there are very few reports that reveal the results you get with the system. That seems odd since the technique is not that new and given all the hype, there must be lots of people using it.

One very optimistic gardener reported “Back in February I commented about the success of my raised hugel bed. After a second season of gardening I will say that it is a dry, dry, raised bed compared to my others,” (note the “dry, dry” phrase is quoted correctly).

But other people do report good results and Dan in this video even compares hugels that are 1, 3 and 4 years old.

But there is a big problem with all of these reports; a complete lack of controls. They build a hugelcultur bed and report on what it does. They don’t compare it to regular garden beds that are made the same way without the  wood. Without a proper control, these anecdotal reports tell us very little about the technique.

More Anecdotal Data

Greg Auton, the Maritime Gardener, gardens in Nova Scotia, a relatively moist climate which can be quite extreme. About a third of his garden uses trenched, low hill hugels (see how he builds them here), and has this to say about hugelkultur.

“The beds where I’ve done this have not been amended in any way since they were built, save the fact that they are always covered with a mulch of some kind. The results have been fantastic, and I don’t need to water them all summer long. To date, I’ve grown just about all of my main veg crops in them (potatoes, squash, tomatoes, carrots, parsnips, cucumbers, beans, etc.”

“In this book ( by Holzer, he talks about his “raised beds” (p33) which are hugelkultur beds. His reason for why they work makes sense to me.”

“It’s a bit of work to make a bed, but once you’ve done that, you really don’t need to cultivate it in any way for years, and the soil stays very loose and workable despite the neglect.”

“I don’t water anything really all summer long. The non-hugel beds have periodic wilting with plants recovering over night; whereas the hugel beds never show wilting.”

Understanding Hugelkultur

When you compare traditional Hugelkultur to other gardening techniques there are three main attributes; An organic layer on top, wood in the bottom and the hill itself.

An Organic Layer

The top layer can be made up of various things but it is essentially a compost pile with added soil.

This layer is not that unusual. The same mix could be layered on soil to make a non-walled raised bed and it is similar to some formulas for making walled raised beds. In a more traditional gardening style it is even layered on soil, and dug in, to create a new garden bed. I don’t think anyone is surprised that this mix grows plants well.

The organic layer is really no different than many other gardening techniques.

Buried Wood

This is a unique feature. It is claimed that this technique is a good way to get rid of excess wood. I can think of easier ways to get rid of wood, so there must be another reason for using it.

It is also claimed that “The wood is a consistent source of long-term nutrients.” Wood is actually a very poor source of nutrients. Its main contribution to soil is humus and carbon.

Apparently, the wood absorbs water which in turn keeps the hill moist so that irrigation is not needed. I have no doubt dead wood absorbs water. I have spent enough time camping in the woods to know that dead wood is almost always too wet to burn, even in a dry summer. When buried in soil it would stay even wetter.

But….. does this wet wood keep the soil above it wetter? When the top of the hill dries out, is there enough water in the wood to keep the soil moist and does it actually release its moisture to the soil?

I suspect the moisture from the wood is only part of the story, and that all the organic matter added above the wood is providing most of the water retention. It is a well known fact that compost holds water.

Here are some anecdotal comments about hugels in dry climates:

What this tells me is that hugels will dry out too much, in areas without enough rain fall. This is a problem with hilled up soil, making this a poor choice for dry climates.

Someone needs to build two identical hills, one with wood and one without, and compare moisture levels, without irrigation. This is a simple experiment that would test the value of the wood.

What Does the Hill Do?

Traditional hugels are built six feet tall. More recently people are building three foot hills, probably because building a six footer takes a lot of wood and work.

What is the purpose of the hill? Is it just there because the trench was not dug deep enough? Why not dig a deeper trench,  add less wood and cover it with organic soil. This would certainly solve the downsides of a hill, including quick drying, being difficult to work on and reduced sun light.

I found no benefit ascribed to the hill by current users, but Sepp Holzer in his book Permaculture does discuss the fact that they make microclimates and they can be used to control runoff on sloped ground. These benefits depend very much on where you garden.

The Downside to Hugelkultur

Even though there is a lack of scientific information we can still analyse the technique.

Rain Runoff

Rain will just run off this hugelkultur hill, photo source: permaculture
Rain will just run off this hugelkultur hill, photo source: Permaculture

Nobody seems to mention it, but when it rains on a pile of soil, the water runs off. It is a terrible way to try and capture rain. That might be a benefit in wet regions, but not for most gardens.

It might be better to create low hugels, or flat topped hugels to help collect the rain.

Weeds on a Hugel

Even the proponents of this technique report a large number of weeds. If you look at pictures of fully grown hugels you will notice lots of weeds. You don’t see nice, clean, weed-free rows as in traditional gardening. I suspect part of this is due to the fact that weeding on a hill is difficult.

Mulching a hill is also a problem.

Who has The Wood?

Hugelkultur is more popular with people with large gardens and those developing a food forest. They have excess wood, but the average gardener does not have easy access to it. In very dry climates wood is scarce.

Even if you have the wood, its a lot of work to build a Hugelkultur garden. I just pile my wood up and let nature take care of it.

Does Hugelkultur Cause Nitrogen Deficiencies?

Wood contains a high level of carbon compared to nitrogen, known as a high C:N ratio. In order for microbes to decompose it, they need to get nitrogen from somewhere and the most likely source is the soil and compost above the wood.

If you mulch with wood chips, you are warned not to dig them into the soil because they rob nitrogen from the plants. This is the same situation and the reason some suggest using old wood. Others build with new wood, but let the pile sit for a year before planting. Both of these would reduce the loss of nitrogen.

Loss of nitrogen will only occur where wood and soil touch. The microbes are not going to suck nitrogen from higher layers in the pile. The other thing to remember is that nitrogen moves easily with water. Every time it rains, the water will wash excess nitrogen from the upper compost layers, down to the wood.

It is unlikely that loss of nitrogen is a problem.

Hugelkultur Walled Raised Bed

Raised bed enthusiasts have adopted the technique because after building the walls they realized it is going to cost a fortune to fill the beds. So they fill the bottom with wood and buy less ingredients to fill the box.

I don’t see this group ascribing much value to the wood, except as a cheap bulk material.

Should You Use Hugelkultur Gardening?

Hugelkultur is considered by some as a very special type of gardening – it’s almost a religion for some. As I was doing a deep dive into the subject, it occurred to me that hugelkultur consists of two simple concepts; bury wood to hold moisture and make tall raised beds. It also includes the concept of adding organic matter to soil, but most gardening techniques do that.

Low hugelkultur raised bed makes more sense, photo source Maritime Gardener
Low hugelkultur raised bed makes more sense than a hill, photo source: Maritime Gardener

Does the wood add any value? Maybe, but maybe all of the benefits ascribed to it are due to the added organic matter? What if the wood were replaced by straw? Or aged manure? Or left out completely? Would the pile work just as well? The complete lack of science on this subject means that we can’t reach any conclusions.

If you have extra wood and you are making a new garden bed, then throw it into the bottom. I would recommend digging a trench first and keeping the wood below grade, unless you garden in a wet climate. Think of the wood as just another form of organic material.

The idea that high, six foot hills are a good place to garden just does not make sense to me. Without science we can’t really conclude anything, so this is just my opinion. I think such high beds would be very awkward for gardening. They would dry out faster, and retain less rain when it does come. And how do you fertilize and mulch such hills? In a hot climate, the shady side might add some benefits, but here in zone 5, we go out of our way to get full sun. I don’t see the benefits of a six foot hill.

Making raised beds with walls makes some sense even though the benefits are usually overstated. Making shorter raised beds without walls also makes sense.

If you want to try hugelkultur, I would suggest digging a trench, adding only enough wood to fill the trench, and then making a low raised bed on top. Put a wall around it if you like, but skip the high hill.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

29 thoughts on “Hugelkultur Gardening Method & Hugelkultur Raised Beds”

  1. I just piled up misc. garden waste of different diameters into a row 20 feet long and 2 feet high, then threw some half-finished compost and a lot of waste soil from planters on top. The next year I grew zucchinis in it and it was fine, but zucchinis are always fine so I mostly consider it a good way to get rid of garden waste and leftover potting soil. Nothing to build a cult around, but I kind of like how it looks.

  2. We live in Wyoming, only eleven inches of rain per year and fine sand is our soil. We trench three feet deep, use wood debris left over from a wild fire, composted manure, straw and garden waste. We strategically placed our trenches to catch runoff from roofs and low areas. These areas are absolutely the most beautiful and productive parts of our gardening and consume the least water. Call it Hugelkultur or whatever; it works for us.

  3. Allow me to share my Hugelkulture adventures . To save on soil filler, I used logs and branches and then compost on top. As the bed in question was part of several in a line, I promptly forgot which. Until the year I decided to try growing sweet potatoes. The tubers were so deformed and misshapen and impossible to clean, let alone cure, that I composted them. When I rotate my crops, now, I skip that bed for root crops. At least until the branches are composted.

    • I’d like to share my anecdote too. I used freshly cut logs also to save on filler too, for 2-ft tall beds. I’ve noticed the soil was very warm in these beds (initially 140F!), possibly because the compost that was mixed in was not aged. Several months later, they are still warmer than ground soil and our other raised beds (85 F vs 70 F).

      I was warned by my extension office the logs would rob the soil of nitrogen. Many of my crops turned yellow and were dying until I began using liquid iron + 15-0-0. I have the exact same soil+compost in another bed, no logs, that is doing well… but so are the melons in the log bed. Just the nightshades and cole crops were suffering.

      I had a soil test performed but regrettably didn’t ask for nitrogen levels to be tested. Maybe because the compost mixed into the soil hadn’t decomposed enough, the nitrogen was tied up regardless of the logs. Hard to draw conclusions from this, but I do know some of my hugelkulture raised beds are cursed. I will remember to test nitrogen levels when I have the soil tested at the end of the season.

      • i’m going to guess that your cold crops were too hot and that it had nothing to do with nitrogen being robbed by the logs! i believe melons are heavy feeders so they would have suffered if it were a nutrient issue. they don’t test nitrogen because it fluctuates too rapidly – it will be different from one day to the next. and if you test it at the end of the season, it won’t be the same come spring. as far as the tomatoes, they don’t seem to like temps above 85f, so it’s possible they were too hot as well. or too wet and roots couldn’t get the calcium out of the soil. god knows!

        good luck!

  4. The “cheap bulk material” for raised beds and rows is the reason I use wood waste in my beds, and I find it genuinely useful.

    I’ve never found it made any difference, positive or negative, on the bed’s performance. Good soil and compost are in limited supply for me, and wood trimmings are in abundance. I’ve also done a thick layer of straw beneath the soil as fill. The difference I found between wood and straw is that the straw breaks down quicker, so I needed to top off the bed by the next year.

    I do raised beds, both walled and shorter raised rows without walls. I am disabled, and digging in our rocky, hard clay soil is not easy for me, which means no dig is the way to go. The older I get, the taller I want my beds to be, just because bending, kneeling down (well, primarily getting *up* again) is more and more difficult. In the future I may have to switch to waist-height beds for that reason, and if so, I think being able to fill the bottom with logs will save me a lot of quality dirt. Currently I can get by with lower beds and berms.

    Despite the fact that height helps me garden, I can’t imagine a traditional hugelkultur with an exposed, super tall hill would work for me. Erosion from our constant drizzle for 10 months of the year, and then drying out from our two hot, very dry months, just doesn’t seem like it would work. Plus the bending down for the lower part of the hill would be a no-go for me personally.

    My yard has plenty of different microclimates and different zones without creating more difficult places to try to figure out what food I can plant in shade.


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